What is polymer processing? Polymer processing technology. Crushing worn tires and tubes

INTRODUCTION

Polymer molecules represent a broad class of compounds, the main distinguishing characteristics of which are high molecular weight and high chain conformational flexibility. It is safe to say that all the characteristic properties of such molecules, as well as the possibilities of their application associated with these properties, are due to the above-mentioned features.

In our urbanized, rapidly developing world, the demand for polymer materials has increased dramatically. It is difficult to imagine the full operation of factories, power plants, boiler houses, educational institutions, electrical household appliances, which surrounds us at home and at work, modern computers, cars and much more without the use of these materials. Whether we want to make a toy or create a spaceship, in both cases we cannot do without polymers. But how can the polymer be given the desired shape and appearance? To answer this question, let’s consider another aspect of polymer technology, namely their processing, which is the subject of this work.

In a broad sense, polymer processing can be thought of as an engineering specialty concerned with converting raw polymer materials into desired end products. Most of the methods currently used in polymer processing technology are modified analogues of methods used in the ceramic and metalworking industries. Indeed, we need to understand the intricacies of polymer processing in order to replace common traditional materials with other materials with improved properties and appearance.

About 50 years ago, there were very limited processes for converting polymers into finished products. Nowadays, there are many processes and methods, the main ones are calendering, casting, direct compression, injection molding, extrusion, blow molding, cold molding, thermoforming, foaming, reinforcement, melt molding, dry and wet molding. The last three methods are used for the production of fibers from fiber-forming materials, and the rest are used for processing plastic and elastomeric materials into industrial products. In the following sections I have attempted to provide a general overview of these important processes. For more detailed information on these and other processes, such as dip and fluidized bed coating, electronic and thermal encapsulation, and welding, please refer to specific textbooks on polymer processing. Issues related to coatings and adhesives are also beyond the scope of this abstract.

Before moving directly to the consideration of methods and methods for processing polymers into final products, it is necessary to find out: what polymers are, what they are like and where they can be used, i.e. what end products can be obtained from polymers? The role of polymers is very important and we must understand the need to recycle them.

1. POLYMERS AND POLYMER MATERIALS

1.1 GENERAL CHARACTERISTICS AND CLASSIFICATION

A polymer is an organic substance whose long molecules are built from identical repeating units - monomers. Based on their origin, polymers are divided into three groups.

Natural are formed as a result of the vital activity of plants and animals and are found in wood, wool, and leather. These are protein, cellulose, starch, shellac, lignin, latex.

Typically, natural polymers undergo purification and modification operations in which the structure of the main chains remains unchanged. The products of such processing are artificial polymers. Examples are natural rubber, which is made from latex, celluloid, which is nitrocellulose plasticized with camphor to increase elasticity.

Natural and artificial polymers have played a major role in modern technology, and in some areas they remain indispensable to this day, for example in the pulp and paper industry. However, the sharp increase in the production and consumption of organic materials occurred due to synthetic polymers – materials obtained by synthesis from low-molecular substances and having no analogues in nature. The development of chemical technology of high-molecular substances is an integral and essential part of modern scientific and technological revolution . No branch of technology, especially new technology, can no longer do without polymers. Based on their chemical structure, polymers are divided into linear, branched, network and spatial.

Molecules linear polymers are chemically inert towards each other and are interconnected only by van der Waals forces. When heated, the viscosity of such polymers decreases and they are able to reversibly transform first into a highly elastic and then into a viscous-flow state (Fig. 1).

Fig.1. Schematic diagram of the viscosity of thermoplastic polymers depending on temperature: T 1 – temperature of transition from a glassy to a highly elastic state, T 2 – temperature of transition from a highly elastic to a viscous flow state.

Since the only effect of heating is a change in plasticity, linear polymers are called thermoplastic. One should not think that the term “linear” means rectilinear; on the contrary, they are more characterized by a jagged or spiral configuration, which gives such polymers mechanical strength.

Thermoplastic polymers can not only be melted, but also dissolved, since van der Waals bonds are easily broken by the action of reagents.

Branched(grafted) polymers are stronger than linear ones. Controlled chain branching is one of the main industrial methods for modifying the properties of thermoplastic polymers.

Mesh structure characterized by the fact that the chains are connected to each other, and this greatly limits movement and leads to changes in both mechanical and chemical properties. Ordinary rubber is soft, but when vulcanized with sulfur, covalent bonds of the S-0 type are formed, and the strength increases. The polymer can acquire a network structure and spontaneously, for example, under the influence of light and oxygen, aging occurs with loss of elasticity and performance. Finally, if the polymer molecules contain reactive groups, then when heated they are connected by many strong cross-links, the polymer becomes cross-linked, i.e. it acquires spatial structure. Thus, heating causes reactions that sharply and irreversibly change the properties of the material, which acquires strength and high viscosity, becomes insoluble and infusible. Due to the high reactivity of molecules, which manifests itself with increasing temperature, such polymers are called thermosetting.

Thermoplastic polymers are produced by the reaction polymerization flowing according to the scheme pMM p(Fig.2), where M - monomer molecule, M p- macromolecule consisting of monomer units, P - degree of polymerization.

During chain polymerization, the molecular weight increases almost instantly, the intermediate products are unstable, the reaction is sensitive to the presence of impurities and, as a rule, requires high pressures. It is not surprising that such a process is impossible under natural conditions, and all natural polymers were formed in a different way. Modern chemistry has created a new tool - the polymerization reaction, and thanks to it a large class of thermoplastic polymers. The polymerization reaction is implemented only in complex equipment of specialized industries, and the consumer receives thermoplastic polymers in finished form.

Reactive molecules of thermosetting polymers can be formed in a simpler and more natural way - gradually from monomer to dimer, then to trimer, tetramer, etc. This combination of monomers, their “condensation”, is called a reaction polycondensation; it does not require high purity or pressure, but is accompanied by a change in the chemical composition, and often the release of by-products (usually water vapor) (Fig. 2). It is this reaction that occurs in nature; it can be easily carried out with only a little heating in the simplest conditions, even at home. Such high manufacturability of thermosetting polymers provides ample opportunities to manufacture various products at non-chemical enterprises, including radio factories.

Regardless of the type and composition of the starting substances and methods of production, polymer-based materials can be classified as follows: plastics, fibers, laminated plastics, films, coatings, adhesives. I will not particularly focus on all of these products; I will only talk about the most widely used ones. It is necessary to show how great the need for polymer materials is in our time, and, consequently, the importance of their processing. Otherwise the problem would simply be unfounded.

1.2 PLASTICS

The word plastic comes from the Greek language and refers to a material that can be compressed or molded into any shape of one's choice. According to this etymology, even clay could be called plastic, but in reality only products made from synthetic materials are called plastics. The American Society for Testing and Materials defines what plastic is as follows: “this is any representative of a wide range of different materials, completely or partially organic in composition, which can be given the desired shape when exposed to temperature and (or) pressure.”

Hundreds of plastics are known. In table 1 presents their main types and shows individual representatives of each species. It should be noted that currently there is no single way to describe the diversity of plastics due to their large number.

Table 1. Main types of plastics

Type	Typical representatives	Type	Typical representatives
Acrylic plastics Aminoplasties	Polymethyl methacrylate (PMMA) Polyacrylonitrile (PAN) Urea-formaldehyde resin Melamine-formaldehyde resin	Polyesters	Unsaturated polyester resins Polyethyl terephthalate (PET) Polyethyl nadipate
Pulp	Ethylcellulose Cellulose acetate Cellulose nitrate	Polyolefins Styrene plastics	Polyethylene (PE) Polypropylene (PP) Polystyrene (PS)
Epoxy plastics	Epoxy resins	Copolymer of styrene and acrylonitrile
Fluoroplastics	Polytetrafluoroethylene (PTFE) Polyvinylidene fluoride	Copolymer of acrylonitrile with styrene and butadiene (ABS)
Phenoplastics	Phenol-formaldehyde resin Phenolfurfural resin	Vinyl plastics	Polyvinyl chloride (PVC) Polyvinyl butyral
Polyamide plastics (nylons)	Polycaprolactam (PA-6) Polyhexam ethylene adipamide (PA-6,6)	Copolymer of vinyl chloride with vinyl acetate

The first thermoplastic to find widespread use was celluloid - an artificial polymer obtained by processing a natural one - cellulose. It played a big role in technology, especially in cinema, but due to its exceptional fire hazard (the composition of cellulose is very close to smokeless gunpowder) already in the middle of the 20th century. its production dropped to almost zero.

The development of electronics, telephone communications, and radio urgently required the creation of new electrical insulating materials with good structural and technological properties. This is how artificial polymers made on the basis of the same cellulose appeared, named after the first letters of their areas of application, etrol. Currently, only 2 ... 3% of the world's polymer production is made up of cellulose plastics, while approximately 75% is synthetic thermoplastics, and 90% of them account for only three: polystyrene, polyethylene, and polyvinyl chloride.

Foaming polystyrene, for example, is widely used as a heat and sound insulating building material. In radio electronics, it is used for sealing products, when it is necessary to ensure minimal mechanical stress, create temporary insulation from the effects of heat emitted by other elements or low temperatures and eliminate their influence on electrical properties, therefore, in on-board and microwave - equipment.

1.3 ELASTOMERS

Elastomers are usually called rubbers. Balloons, shoe soles, splints, surgical gloves, garden hoses are typical examples of products made from elastomers. A classic example of elastomers is natural rubber.

The rubber macromolecule has a helical structure with an identity period of 0.913 nm and contains more than 1000 isoprene residues. The structure of the macromolecule of rubber ensures its high elasticity - the most important technical property. Rubber has the amazing ability to reversibly stretch up to 900% of its original length.

A type of rubber is the less elastic gutta-percha, or balata, the juice of some rubber-bearing plants growing in India and the Malay Peninsula. Unlike rubber, the gutta-percha molecule is shorter and has a trans-1,4 structure with an identity period of 0.504 nm.

The outstanding technical significance of natural rubber, the absence of economically viable sources in a number of countries, including the Soviet Union, and the desire to have materials superior to natural rubber in a number of properties (oil resistance, frost resistance, abrasion resistance) stimulated research into the production of synthetic rubber. .

There are several synthetic elastomers currently in use. These include polybutadienes, styrene-butadiene, acrylonitrile-butadiene (nitrile rubber), polyisoprene, polychloroprene (neoprene), ethylene-propylene, isoprene-isobutylene (butyl rubber), polyfluorocarbon, polyurethane, and silicone rubbers. The raw material for producing synthetic rubber using the Lebedev method is ethyl alcohol. Now the production of butadiene from butane through the catalytic dehydrogenation of the latter has been developed.

Scientists have been successful and today more than one third of the rubber produced in the world is made from synthetic rubber. Rubber made a huge contribution to the technological progress of the last century. Let us at least remember rubber boots and various insulating materials, and the role of rubber in the most important sectors of the economy will become clear to us. More than half of the world's elastomer production is spent on tire production. To make tires for a small car you need about 20 kg of rubber, of different grades and brands, and for a dump truck almost 1900 kg. A smaller portion goes to other types of rubber products. Rubber makes our lives more convenient.

1.4 FIBERS

We all know fibers natural origin, such as cotton, wool, linen and silk. We are also familiar with synthetic fibers made from nylon, polyester, polypropylene and acrylics. The main distinguishing feature of the fibers is that their length is hundreds of times greater than their diameter. If natural fibers (except silk) are staple fibers, then synthetic fibers can be obtained both in the form of continuous threads and in the form of staple fiber.

From a consumer's perspective, fibers can be of three types; everyday use, safety and industrial.

Convenience fibers are fibers used to make outerwear and outerwear. This group includes fibers for the manufacture of underwear, socks, shirts, suits, etc. These fibers must have appropriate strength and elongation, softness, non-flammability, absorb moisture and be easily dyed. Typical representatives of this class of fibers are cotton, silk, wool, nylon, polyesters and acrylates.

Safety fibers are those used to make carpets, curtains, chair covers, draperies, etc. Such fibers must be tough, strong, durable and wear-resistant. From a safety point of view, the following requirements are imposed on these fibers: they must be low in flammability, not spread flames and, when burning, emit a minimum amount of heat, smoke and toxic gases. By adding small amounts of substances containing atoms such as B, N, Si, P, C1, Br or Sb to consumer fibers, it is possible to impart flame retardant properties to them and thus turn them into safe fibers. The introduction of modifying additives into fibers reduces their flammability, reduces the spread of flame, but does not lead to a reduction in the release of toxic gases and smoke during combustion. Studies have shown that aromatic polyamides, polyimides, polybenzimidazoles and polyoxydiazoles can be used as safe fibers. However, when these fibers burn, toxic gases are released because their molecules contain nitrogen atoms. Aromatic polyesters do not have this drawback.

Industrial fibers are used as reinforcements in composites. These fibers are also called structural fibers because they have high modulus, strength, heat resistance, stiffness, and durability. Structural fibers are used to strengthen products such as rigid and flexible pipes, tubes and hoses, as well as in composite structures called fibres, which are used in the construction of ships, cars, aircraft and even buildings. This class of fibers includes uniaxially oriented fibers of aromatic polyamides and polyesters, carbon and silicon fibers.

2. POLYMER PROCESSING

2.1 COMPOUNDING

Pure polymers obtained from industrial plants after isolation and purification are called "primary" polymers or "virgin" resins. With the exception of some polymers such as polystyrene, polyethylene, polypropylene, virgin polymers are generally not suitable for direct recycling. Virgin polyvinyl chloride, for example, is a horn-like material and cannot be molded without first being softened by adding a plasticizer. Similarly, molding natural rubber requires the addition of a vulcanizing agent. Most polymers are protected from thermal, oxidative and photodegradation by introducing suitable stabilizers into them. Adding dyes and pigments to the polymer before molding allows you to obtain products of a wide variety of colors. To reduce friction and improve polymer flow within processing equipment, lubricants and substances are added to most polymers to improve processing properties. Fillers are usually added to polymers to give them special properties and reduce the cost of the final product.

The process involving the addition of ingredients such as plasticizers, vulcanizing agents, hardeners, stabilizers, fillers, dyes, flame retardants and lubricants into the primary polymer is called “compounding”, and mixtures of polymers with these additives are called “compounds”.

Primary plastic polymers, such as polystyrene, polyethylene, polymethyl methacrylate and polyvinyl chloride, are usually found in the form of free-flowing fine powders. Ingredients in fine powder or liquid form are mixed with the powdered virgin polymer using planetary mixers, V-mixers, helical belt mixers, Z-mixers or tumblers. The displacement can be carried out either at room temperature or at elevated temperature, which, however, must be well below the softening temperature of the polymer. Liquid prepolymers are mixed using simple high-speed mixers.

Primary elastomeric polymers, such as natural rubber, styrene butadiene rubber or nitrile rubber, are produced in the form of crumbs, compressed into thick plates called "bales". They are typically mixed with vulcanizing agents, catalysts, fillers, antioxidants and lubricants. Because elastomers are not free-flowing powders like virgin plastics, they cannot be mixed with the above ingredients using the methods used for virgin plastics. Mixing of primary plastic polymers with other components of the compound is achieved by mixing, while obtaining a compound of primary elastomers involves rolling the crumbs into plastic sheets and then introducing the required ingredients into the polymer. Compounding of elastomers is carried out either in a two-roll rubber mill or in a Banbury mixer with internal mixing. Elastomers in the form of latex or low molecular weight liquid resins can be mixed by simple mixing using high-speed mixers. In the case of fiber-forming polymers, compounding is not carried out. Components such as lubricants, stabilizers and fillers are usually directly added to the polymer melt or solution immediately before the yarn is spun.

2.2 PROCESSING TECHNOLOGY

The fact that polymeric materials are used in a variety of forms, such as rods, tubes, sheets, foams, coatings or adhesives, and as extruded products, means that there are a variety of ways to process polymer compounds into final products. Most polymer products are produced by either molding, processing, or casting liquid fornopolymers into a mold and then curing or cross-linking them. The fibers are obtained through the spinning process.

The molding process can be compared, for example, with modeling a figure from clay, and the processing process can be compared with cutting out the same figure from a piece of soap. During the molding process, a compound in the form of powder, flakes, or granules is placed in a mold and subjected to heat and pressure to form the final product. The processing process produces products in simple shapes such as sheets, rods or tubes using punching, stamping, gluing and welding.

Before moving on to a discussion of the various methods for processing polymers, recall that polymer materials can be thermoplastic or thermoset (thermoset). Once thermoplastic materials have been molded under heat and pressure, they must be cooled below the softening temperature of the polymer before being released from the mold, otherwise they will lose their shape. In the case of thermosetting materials, there is no such need, since after a single combined exposure to temperature and pressure, the product retains its acquired shape even when it is released from the mold at high temperature.

2.3 CALENDARING

The calendering process is commonly used to produce continuous films and sheets. The main part of the calendering apparatus (Fig. 1) is a set of smoothly polished metal rollers rotating in opposite directions, and a device for precisely adjusting the gap between them. The gap between the rolls determines the thickness of the calendered sheet. The polymer compound is fed to hot rolls, and the sheet coming from these rolls is cooled as it passes through the cold rolls. At the last stage, the sheets are wound into rolls, as shown in Fig. 1. However, if instead of sheets it is required to obtain thin polymer films, a series of rolls with a gradually decreasing gap between them is used. Typically polymers such as polyvinyl chloride, polyethylene, rubber, and butadiene-styrene-acrylonitrile copolymer are calendered into sheets.

Rice. 1. Diagram of the calendering apparatus

/ - polymer compound; 2 - calender rolls: hot (3) and cold (4); 5 - calendered sheet; b - guide rollers; 7 - winder

When using profiled rolls in a calendering machine, it is possible to obtain embossed sheets of various designs. Various decorative effects, such as marble imitation, can be achieved by introducing a mixture of compounds of different colors into the calender. Marbling technology is commonly used in the production of PVC floor tiles.

2.4 CASTING

MOLD CASTING. This is a relatively inexpensive process that consists of processing a liquid prepolymer into solid products of the required shape. This method can be used to produce sheets, pipes, rods, etc. products of limited length. The mold casting process is shown schematically in Fig. 2. In this case, the prepolymer, mixed in appropriate proportions with the hardener and other ingredients, is poured into a Petri dish, which serves as a mold. The Petri dish is then placed in an oven heated to the required temperature for several hours until the hardening reaction is complete. After cooling to room temperature, the solid product is removed from the mold. A solid cast in this way will have the shape of the internal relief of a Petri dish.

Rice. 2. The simplest image of the casting process in a mold

b - filling a Petri dish with a prepolymer and hardener; b - heating in an oven; b - removing the cooled product from the mold

If instead of a Petri dish you use a cylindrical glass tube closed at one end, you can obtain a product in the form of a cylindrical rod. In addition, instead of prepolymer and hardener, a mixture of monomer, catalyst and other ingredients heated to the polymerization temperature can be poured into the mold. Polymerization in this case will occur inside the mold until a solid product is formed. Acrylics, epoxies, polyesters, phenols and urethanes are suitable for mold casting.

Casting molds are made of alabaster, lead or glass. During the curing process, the polymer block shrinks, which makes it easier to release from the mold.

ROTARY CASTING. Hollow products, such as balls and dolls, are produced through a process called "rotary casting." The apparatus used in this process is shown in Fig. 3.

The thermoplastic material compound in the form of a fine powder is placed in a hollow mold. The apparatus used has a special device for simultaneous rotation of the mold around the primary and secondary axes. The mold is closed, heated and rotated. This results in a uniform distribution of molten plastic over the entire inner surface of the hollow mold. The rotating mold is then cooled cold water. When cooled, the molten plastic material, uniformly distributed over the inner surface of the mold, hardens. The mold can now be opened and the final product removed.

A liquid mixture of a thermosetting prepolymer and a hardener can also be loaded into the mold. Hardening in this case will occur during rotation under the influence of elevated temperature.

Rotational casting produces products from polyvinyl chloride, such as overshoes, hollow balls or doll heads. Hardening of polyvinyl chloride is carried out by physical gelation between polyvinyl chloride and a liquid plasticizer at temperatures of 150-200°C. Fine particles of polyvinyl chloride are uniformly dispersed in a liquid plasticizer along with stabilizers and dyes, thus forming a substance with a relatively low viscosity. This paste-like material, called "plastisol", is loaded into a mold and the air is pumped out of it. Then the mold begins to rotate and heat to the required temperature, which leads to the gelation of polyvinyl chloride. The wall thickness of the resulting product is determined by the gelation time.

Fig.3. In the rotational casting process, hollow molds filled with polymer material are simultaneously rotated around a primary and secondary axes.

1 - primary axis; 2 - secondary axis; 3 - split mold part; 4 - mold cavities; 5 - gear housing; b-to the motor

Once the required wall thickness is achieved, excess plastisol is removed for a repeat cycle. For final homogenization of the mixture of polyvinyl chloride particles and plasticizer, the gel-like product inside the mold is heated. The final product is removed from the mold after it has been cooled with a stream of water. The rotational casting method using liquid material is known as the "hollow pour-and-rotate molding" method.

INJECTION MOLDING. The most convenient process for producing thermoplastic polymer products is the injection molding process. Despite the fact that the cost of equipment in this process is quite high, its undoubted advantage is high productivity. In this process, a measured amount of molten thermoplastic polymer is injected under pressure into a relatively cold mold, where it solidifies into the final product.

The injection molding apparatus is shown in Fig. 6. The process consists of feeding a compounded plastic material in the form of granules, tablets or powder from a hopper at certain intervals into a heated horizontal cylinder, where it is softened. A hydraulic piston provides the pressure necessary to force the molten material along the cylinder into a mold located at the end. As the polymer mass moves along the hot zone of the cylinder, a device called a “torpedo” promotes uniform distribution of the plastic material along the inner walls of the hot cylinder, thus ensuring uniform distribution heat throughout the entire volume. The molten plastic material is then injected through the injection hole into the mold cavity.

In its simplest form, a mold is a system of two parts: one of the parts is moving, the other is stationary (see Fig. 6). The stationary part of the mold is fixed at the end of the cylinder, and the movable part is removed and put on it.

Using a special mechanical device, the mold is tightly closed, and at this time the molten plastic material is injected under a pressure of 1500 kg/cm. The closing mechanical device must be made to withstand high operating pressures. The uniform flow of molten material in the internal areas of the mold is ensured by preheating it to a certain temperature. Typically this temperature is slightly lower than the softening temperature of the plastic material being pressed. After the mold is filled with molten polymer, it is cooled with circulating cold water and then opened to remove the finished product. This entire cycle can be repeated many times, both manually and automatically.

CASTING OF FILM. The casting method is also used for the production of polymer films. In this case, a polymer solution of appropriate concentration is gradually poured onto a metal belt moving at a constant speed (Fig. 4), on the surface of which a continuous layer of polymer solution is formed.

Fig.4. Scheme of the film casting process

/ - polymer solution; 2 - distribution valve; 3 - the polymer solution spreads to form a film; 4 - the solvent evaporates; 5 - endless metal belt; 6 - continuous polymer film; 7 - winding reel

When the solvent evaporates in a controlled manner, a thin polymer film is formed on the surface of the metal belt. After this, the film is removed by simple peeling. Most industrial cellophane sheets and photographic films are produced using this method.

2.5 DIRECT PRESSING

The direct compression method is widely used to produce products from thermoset materials. Figure 5 shows a typical mold used for direct compression. The mold consists of two parts - upper and lower, or a punch (positive form) and a matrix (negative form). There is a recess at the bottom of the mold and a protrusion at the top. The gap between the protrusion of the upper part and the recess of the lower part in a closed mold determines the final appearance of the pressed product.

In the direct compression process, the thermoset material is subjected to a single application of temperature and pressure. The use of a hydraulic press with heated plates allows you to obtain the desired result.

Fig.5. Schematic illustration of a mold used in the direct molding process

1 - mold cavity filled with thermosetting material; 2 - guide pins; 3 - burr; 4 - molded product

Temperature and pressure during pressing can reach 200 °C and 70 kg/cm2, respectively. Operating temperature and pressure are determined by the rheological, thermal and other properties of the pressed plastic material. The mold recess is completely filled with a polymer compound. When the mold is closed under pressure, the material inside it is compressed and pressed into the desired shape. Excess material is forced out of the mold in the form of a thin film called "burr." Under the influence of temperature, the pressed mass hardens. No cooling is required to release the final product from the mold.

Fig..6. Schematic illustration of the injection molding process

1 - compounded plastic material; 2 - loading funnel; 3 - piston; 4 - electric heating element; 5 - stationary part of the mold;

6 - movable part of the mold; 7 - main cylinder; 8 - torpedo; 9 - softened plastic material; 10 - mold; 11 - product molded by injection molding

2.6 MOLDING

AIR MOLDING. A large number of hollow plastic products are produced by blow molding: canisters, soft drink bottles, etc. The following thermoplastic materials can be blow molded: polyethylene, polycarbonate, polyvinyl chloride, polystyrene, nylon, polypropylene, acrylics, acrylonitrile, acrylonitrile-butadiene-styrene polymer, however In terms of annual consumption, high-density polyethylene ranks first.

Blow molding has its origins in the glassblowing industry. A diagram of this process is given in Fig. 7.

A hot softened thermoplastic tube, called a "blank", is placed inside a hollow two-piece mold. When the mold is closed, both halves clamp between one end of the mold and the air needle located at the other end of the tube.

Fig.7. Schematic diagram explaining the stages of the blow molding process

A - a workpiece placed in an open mold; b - closed mold;

c - blowing air into the mold; d - opening of the mold. 1- blank;

2 - needle for air supply; 3 - Press form; 4 - air; 5 - product made by blow molding

Under the influence of pressure supplied from the compressor through the needle, the hot workpiece is inflated like a ball until it comes into tight contact with the relatively cold inner surface of the mold. The mold is then cooled, opened and the finished solid thermoplastic product is removed.

The preform for blow molding can be produced by injection molding or extrusion, and depending on this, the method is called injection blow molding or extrusion blow molding, respectively.

FORMING SHEET THERMOPLASTS. Thermoplastic sheet molding is an extremely important process for the production of 3D plastic products. Using this method, even large products such as submarine hulls are produced from sheets of acrylonitrile butadiene styrene.

The scheme of this Process is as follows. The thermoplastic sheet is heated to its softening temperature. Then the punch presses the hot flexible sheet into the matrix of the metal mold (Fig. 9), while the sheet takes a certain shape. When cooled, the molded product hardens and is removed from the mold.

In the modified method, under the influence of vacuum, the hot sheet is sucked into the matrix cavity and takes the required shape (Fig. 10). This method is called vacuum forming method.

2.7 EXTRUSION

Extrusion is one of the cheapest methods for producing common plastic products such as films, fibers, tubes, sheets, rods, hoses and belts, the profile of these products being determined by the shape of the extruder die exhaust port. Under certain conditions, molten plastic is extruded through the outlet of the extruder head, which gives the desired profile to the extrudate. A diagram of the simplest extrusion machine is shown in Fig. 8.

Figure 8. Schematic representation of a simple extrusion machine

1 - loading funnel; 2 - auger; 3 - main cylinder; 4 - heating elements; 5 - extruder head outlet, A - Loading Zone; b - compression zone; in ~ homogenization zone

In this machine, powder or granules of compounded plastic material are loaded from a hopper into an electrically heated cylinder to soften the polymer. A spiral-shaped rotating screw ensures the movement of hot plastic mass along the cylinder. Since friction occurs when the polymer mass moves between the rotating screw and the cylinder, this leads to the release of heat and, consequently, to an increase in the temperature of the processed polymer. During this movement from the hopper to the outlet of the extruder head, the plastic mass passes through three clearly separated zones: the loading zone (a), the compression zone (b) and the homogenization zone (V)(see Figure 9).

Each of these zones contributes to the extrusion process. The loading zone, for example, receives the polymer mass from the hopper and directs it to the compression zone, this operation takes place without heating.

Rice. 9. Scheme of the thermoplastic sheet molding process

1 - sheet of thermoplastic material; 2 - clamp; 3 - punch; 4 - sheet softened by heat; 5 - matrix; 6 - product obtained by molding thermoplast sheets

Fig. 10. Diagram of the vacuum molding process for thermoplastics

1 - clamp; 2 - thermoplastic sheet; 3 - Press form; 4 - product obtained by vacuum molding of thermoplastics

In the compression zone, heating elements melt the powder load, and a rotating screw compresses it. Then the paste-like molten plastic material enters the homogenization zone, where it acquires a constant flow rate due to the screw thread of the screw.

Under the influence of pressure created in this part of the extruder, the polymer melt is fed to the outlet of the extruder head and exits with the desired profile. Due to the high viscosity of some polymers, it is sometimes necessary to have another zone, called a working zone, where the polymer is subjected to high shear loads to improve mixing efficiency. The extruded material of the required profile leaves the extruder in a very hot state (its temperature ranges from 125 to 350 ° C), and it requires rapid cooling to maintain its shape. The extrudate is fed onto a conveyor belt passing through a vat of cold water and solidified. To cool the extrudate, blowing with cold air and spraying with cold water is also used. The formed product is subsequently either cut or wound into coils.

The extrusion process is also used to coat wires and cables with polyvinyl chloride or rubber, and rod-shaped metal rods with suitable thermoplastic materials.

2.8 FOAMING

Foaming is a simple method for producing foam and sponge-like materials. The special properties of this class of materials - shock-absorbing ability, light weight, low thermal conductivity - make them very attractive for use for various purposes. Common foaming polymers are polyurethanes, polystyrene, polyethylene, polypropylene, silicones, epoxies, PVC, etc. The foam structure consists of isolated (closed) or interpenetrating (open) voids. In the first case, when the voids are closed, they can contain gases. Both types of structures are schematically presented in Fig. 11.

Fig. 11. Schematic representation of open and closed cellular structures formed during the foaming process

1- discrete (closed) cells; 2 - interpenetrating (open) cells;

3 - cell walls

There are several methods for producing foamed or cellular plastics. One is to blow air or nitrogen through the molten compound until it foams completely. The foaming process is facilitated by the addition of surfactants. Once the required degree of foaming is achieved, the matrix is ​​cooled to room temperature. In this case, the thermoplastic material hardens into a foamed state. Thermoset liquid prepolymers can be cold foamed and then heated until they are completely cured. Typically, foaming is achieved by adding foaming or gas-forming agents to the polymer mass. Such agents are low molecular weight solvents or certain chemical compounds. The boiling process of solvents such as n-pentane and n-hexane at the solidification temperatures of polymer materials is accompanied by an intense process of vaporization. On the other hand, some chemical compounds may decompose at these temperatures, releasing inert gases. Thus, azo-bis-isobutyronitrile thermally decomposes, releasing a large volume of nitrogen, which is released into the polymer matrix as a result of the reaction between isocyanate and water; it is also used for the production of foam materials, for example polyurethane foam:

Since polyurethanes are produced by reacting a polyol with a diisocyanate, additional small amounts of diisocyanate and water must be added to foam the reaction product.

So, a large amount of vapors or gases released by foaming and gas formers leads to foaming of the polymer matrix. The polymer matrix in the foamed state is cooled to temperatures below the softening temperature of the polymer (in the case of thermoplastic materials) or subjected to a curing or cross-linking reaction (in the case of thermoset materials), as a result of which the matrix acquires the rigidity necessary to maintain the foam structure. This process is called the "foam stabilization" process. If the matrix is ​​not cooled below the softening point or cross-linked, the gases filling it leave the pore system and the foam collapses.

Foams can be produced in flexible, rigid and semi-rigid forms. In order to obtain foam products directly, foaming should be carried out directly inside the mold. Foam sheets and cores can also be used to make a variety of products. Depending on the nature of the polymer and the degree of foaming, the density of foam plastics can range from 20 to 1000 kg/cm 3 . The use of foam plastics is very diverse. For example, the automotive industry uses large quantities of PVC and polyurethane foams for upholstery. These materials also play an important role in the manufacture of furniture. Rigid polystyrene foams are widely used for packaging and building insulation. Rubber foams and polyurethane foams are used for stuffing mattresses, etc. Rigid polyurethane foams are also used for thermal insulation of buildings and for the manufacture of prosthetics.

2.9 REINFORCEMENT

By reinforcing a plastic matrix with high-strength fibers, systems called “fiber-reinforced plastics” (FRPs) are obtained. AVPs have very valuable properties: they are distinguished by a high strength-to-weight ratio, significant corrosion resistance and ease of manufacture. The fiber reinforcement method can be used to produce a wide range of products. For example, when creating artificial satellites in AVP, designers and creators of spacecraft are primarily attracted by the amazingly high strength-to-weight ratio. Beautiful appearance, low weight and corrosion resistance make it possible to use AVP for plating sea vessels. In addition, AVP is even used as a material for tanks in which acids are stored.

Let us now take a closer look at the chemical composition and physical nature of these unusual materials. As noted above, they are a polymer material, the special properties of which are due to the introduction of reinforcing fibers into it. The main materials from which reinforcing fibers are made (both finely cut and long) are glass, graphite, aluminum, carbon, boron and beryllium. The most recent advances in this area involve the use of all-aromatic polyamide reinforcement fibers, which provides more than 50% weight reduction compared to traditional fiber-based reinforced plastics. Natural fibers are also used for reinforcement, such as sisal, asbestos, etc. The choice of reinforcing fiber is primarily determined by the requirements for the final product. However, glass fibers remain widely used to this day and still make a major contribution to the industrial production of AVP. The most attractive properties of glass fibers are low coefficient of thermal expansion, high dimensional stability, low production cost, high tensile strength, low dielectric constant, non-flammability and chemical resistance. Other reinforcing fibers are used mainly in cases where some additional properties are required for the operation of AVP in specific conditions, despite their higher cost compared to glass fibers.

AVP is produced by bonding fibers to a polymer matrix and then hardening it under pressure and temperature. Reinforcing additives can be in the form of finely chopped fibers, long threads and fabrics. The main polymer matrices used in AVP are polyesters, epoxies, phenols, silicones, melamine, vinyl derivatives and polyamides. Most AVPs are produced on the basis of polyester polymers, the main advantage of which is their low cost. Phenolic polymers are used in cases where high heat resistance is required. AVP acquires extremely high mechanical properties when using epoxy resins as a polymer matrix. The use of silicone polymers gives AVP excellent electrical and thermal properties.

Currently, there are several methods of plastic reinforcement. The most commonly used ones are: 1) hand layering method, 2) fiber winding method, and 3) spray impregnation method.

METHOD OF LAYERING SHEETS BY MANUAL. It is likely that this is the simplest method of reinforcing plastics. In this case, the quality of the final product is largely determined by the skill and skill of the operator. The whole process consists of the following stages. First, the mold is coated with a thin layer of adhesive lubricant based on polyvinyl alcohol, silicone oil or paraffin. This is done to prevent the final product from sticking to the mold. Then the mold is covered with a layer of polymer, on top of which fiberglass or mat is placed. This fiberglass fabric, in turn, is coated with another layer of polymer.

Fig. 12. Schematic illustration of the manual layering method

1 - alternating layers of polymer and fiberglass; 2 - Press form; 3 - rolling roller

All this is tightly rolled with rollers to uniformly press the fiberglass onto the polymer and remove air bubbles. The number of alternating layers of polymer and fiberglass determines the thickness of the sample (Fig. 12).

Then, at room or elevated temperature, the system hardens. Once cured, the reinforced plastic is removed from the mold and undergoes stripping and final finishing. This method produces sheets, car body parts, ship hulls, pipes and even building fragments.

FIBER WINDING METHOD. This method is very widely used for the production of reinforced plastic products such as high-pressure cylinders, chemical storage tanks and rocket motor casings. It consists of passing a continuous monofilament, fiber, bundle of fibers or woven tape through a bath of resin and hardener. As the fiber exits the bath, excess resin is squeezed out. The resin-impregnated fibers or tape are then wound onto a core of the desired shape and cured by heat.

Fig. 13. Schematic illustration of the fiber winding method

1- feed reel; 2 - continuous thread; 3 - unit for fiber impregnation and resin extraction; 4 - core; 5 - resin-impregnated fibers wound on a core

The winding machine (Fig. 13) is designed so that the fibers can be wound onto the core in a certain way. The tension of the fiber and the method of winding it are very important from the point of view of the final deformation properties of the finished product.

SPRAYING METHOD. This method uses a spray gun with a multi-strand head. Jets of resin, hardener and chopped fiber are simultaneously fed from a spray gun onto the surface of the mold (Fig. 14), where they form a layer of a certain thickness. Cut fiber of a certain length is obtained by continuously feeding fibers into the grinding head of the apparatus. After reaching the required thickness, the polymer mass is cured by heating. Spraying is an express method for covering large surfaces. Many modern plastic products, such as loading platforms, storage tanks, truck bodies and ship hulls, are produced using this method.

Fig. 14. Schematic representation of the spraying method

1 - shape; 2 - sprayed mixture of chopped fiber and resin; 3 - a stream of chopped fiber; 4 - continuous fiber; 5- resin; 6- hardener; 7 - unit for cutting fiber and spraying; 8 - jet of resin

OTHER METHODS. In addition to the methods described above, others are known in the production of reinforced plastics, each of which has its own specific purpose. Thus, the continuous laminate method is used to produce continuous sheets of reinforced laminates of varying thicknesses. In this process, each individual layer of woven tape coming from rolls is impregnated with resin and hardener and then pressed together by passing through a hot roll system. After hardening under the influence of temperature, laminated plastic I of the required thickness is obtained (Fig. 15). The thickness of the material can be varied by changing the number of layers.

Fig. 15. Schematic representation of the continuous laminate production method

1- feed coils; 2 - continuous sheets of fiberglass; 3 - bath for impregnation in a mixture of resin and hardener; 4 - continuous laminate; 5 - laminated plastic, cut into pieces of the required size

Another method, known as the oriented fiber plastic method, can be used to make products such as hollow rods or fishing rods from continuous bundles of fibers. This process is relatively simple. A continuous bundle of fibers, pre-treated with resin and hardener, is pulled through a die of the appropriate profile (Fig. 16), heated to a certain temperature. At the outlet of the die, the profiled product continues to be heated. The cured profile is pulled from the die by a system of rotating rolls. This process is somewhat reminiscent of extrusion, with the only difference being that during extrusion, the polymer material is pushed through the die from the inside using a rotating screw, and in the described method, the material is pulled through the outlet of the die from the outside.

Fig. 16. Schematic representation of the method for producing uniaxially oriented fibrous plastic

1 - a continuous bundle of fibers impregnated with resin and hardener; 2 - heating element; 3 - die; 4 - rotating drawing rolls; 5 - finished product, cut into pieces; 6 - finished product profile

In addition, the mixture containing cut fibers, resin and hardener can be molded into any other suitable method, for example by direct pressing. Thermoplastic materials filled with cut fibers can be molded by direct compression, injection molding or extrusion to produce a final product with improved mechanical properties.

2.10 FIBER SPINNING

Polymer fibers are produced through a process called spinning. There are three fundamentally different spinning methods: melt spinning, dry spinning and wet spinning. In the melt spinning process the polymer is in a molten state and in other cases it is in the form of solutions. However, in all these cases, the polymer, in a molten or dissolved state, flows through a multi-channel die, which is a plate with very small holes for the fibers to exit.

MELT SPINNING. In its simplest form, the spunmelt process can be represented as follows. Initially, the polymer flakes are melted on a heated grid, turning the polymer into a viscous mobile liquid. Sometimes during the heating process, lumps form due to cross-linking processes or thermal destruction. These lumps can be easily removed from the hot polymer melt by passing through a block filter system. In addition, to prevent oxidative destruction, the melt should be protected from atmospheric oxygen. This is achieved mainly by creating an inert atmosphere of nitrogen, COd and water vapor around the polymer melt. A dosing pump supplies the polymer melt at a constant speed to a multi-channel die (die). The polymer melt passes through a system of fine holes in the die and exits in the form of continuous and very thin monofilaments. Upon contact with cold air, the fibers emerging from the dies instantly harden. The cooling and hardening processes can be greatly accelerated by blowing cold air. The solid monofilaments emerging from the spinnerets are wound onto spools.

An important feature to consider in the melt spinning process is that the diameter of the monofilament is largely dependent on the speed at which the molten polymer passes through the spinneret and the speed at which the monofilament is pulled from the spinneret and wound onto spools.

Fig. 17. Schematic representation of dry spinning processes (A) and spinning from melt (b)

1 - hopper; 2 - polymer flakes; 3 - heated grate; 4 - hot polymer; 5 - dosing pump; b - melt; 7-multi-channel mouthpiece, 8 - freshly spun fiber; 9 - coil; 10 - polymer solution; 11 - filter;

12 - dosing pump; 13 - multi-channel mouthpiece; 14 - freshly spun fiber; 15 - per reel

DRY SPINNING. Large quantities of traditional polymers such as PVC or polyacrylonitrile are processed into fibers on a large scale through the dry spinning process. The essence of this process is shown in Fig. 17. The polymer is dissolved in an appropriate solvent to form a highly concentrated solution. The viscosity of the solution is adjusted by increasing the temperature. A hot viscous polymer solution is forced through dies, thus obtaining thin continuous streams. The fiber from these streams is formed by simple evaporation of the solvent. Solvent evaporation can be accelerated by blowing with a counter flow of dry nitrogen. The fibers formed from the polymer solution are eventually wound onto spools. The fiber spinning speed can reach 1000 m/min. Industrial cellulose acetate fibers obtained from a 35% solution of the polymer in acetone at 40 °C are a typical example of the production of fibers by dry spinning.

WET SPINNING. In wet spinning, as in dry spinning, highly concentrated polymer solutions are used, the high viscosity of which can be reduced by increasing the spinning temperature. The details of the wet spinning process are shown in Fig. 18. In the wet spinning process, a viscous polymer solution is processed into thin strings when passed through dies. Then these polymer streams enter a coagulation bath with a precipitant, where the polymer is precipitated from the solution in the form of thin threads, which, after washing, drying, etc., are collected on spools. Sometimes, during the wet spinning process, lumps are formed instead of continuous threads, which occurs as a result of the breakage of the stream flowing from the spinneret under the influence of surface tension forces.

Fig. 18. Schematic representation of the wet spinning process

1 - polymer solution; 2 - filter; 3 - dosing pump; 4 - multi-channel mouthpiece; 5 - precipitant; 6 - freshly spun fiber; 7 - bath for coagulation and sedimentation; 8 - rinsing bath; 9 - drying; 10 - per reel

This can be avoided by increasing the viscosity of the polymer solution. Coagulation, which is the limiting stage of wet spinning, is a rather slow process, which explains the low solution spinning speed compared to others, equal to 50 m/min. In industry, the wet spinning process is used to produce fibers from polyacrylonitrile, cellulose, viscose fiber, etc.

SINGLE-AXIS ORIENTATION. During the process of spinning fibers from a polymer melt or solution, the macromolecules in the fiber are not oriented and, therefore, their degree of crystallinity is relatively low, which undesirably affects the physical properties of the fiber. To improve the physical properties of the fibers, they are subjected to an operation called uniaxial drawing using a certain type of stretching apparatus.

The main feature of the device is the presence of a two-roller system A And IN(Fig. 19), rotating at different speeds. Video clip IN rotates 4-5 times faster than the roller A. The spun thread is passed successively through a roller A, tension pin 3 and video IN. Because the roller IN rotates at a speed greater than the roller A, the fiber is pulled out under the load specified by the pin 3. Fiber drawing is carried out in the area 2. After going through the cutscene IN an elongated polymer thread is wound onto a metal bobbin. Despite the fact that during the drawing process the diameter of the thread decreases, its strength properties are significantly improved due to the orientation of the macromolecules parallel to the fiber axis.

Fig. 19. Schematic representation of the apparatus for uniaxial orientation

1- undrawn thread; 2 - exhaust zone; 3 - stretch pin; 4- drawn fiber

POST-PROCESSING OF FIBERS. To improve the beneficial properties of fibers, they are often subjected to additional special processing: cleaning, lubricating, sizing, dyeing, etc.

Soaps and other synthetic detergents are used for cleaning. Cleaning is nothing more than removing dirt and other impurities from the surface of the fiber. Lubrication involves treating the fibers to protect

them from friction with adjacent fibers and rough metal surfaces during processing. Natural oils are mainly used as lubricants. Lubrication also reduces static electricity that accumulates on the fibers.

Sizing is the process of protective coating of fibers. Polyvinyl alcohol or gelatin are used as sizing materials for most fibers. Sizing helps keep the fibers within a compact bundle and thus ensures uniform weaving. Before dyeing the fabric, the sizing should be removed by washing in water.

To dye the fibers, they are placed in a dye solution, the molecules of which usually penetrate only into the amorphous areas of the fiber.

Fibers based on cellulose or proteins quickly adsorb acidic dyes, which easily bind to the amino or hydroxyl groups of polymers. The dyeing process for synthetic fibers such as polyesters, polyamides or acrylics is much slower. In this case, the dyeing speed can be increased by increasing the temperature. Dyeing fibers based on polyvinyl chloride, polyethylene, etc. is practically impossible without introducing active absorption centers into them during copolymerization and chemical oxidation.

CONCLUSION

As previously noted, polymers include numerous natural compounds: proteins, nucleic acids, cellulose, starch, rubber and other organic substances. A large number of polymers are produced synthetically based on the simplest compounds of elements of natural origin through polymerization reactions, polycondensation, and chemical transformations.

In the early 60s, polymers were considered only cheap substitutes for scarce natural raw materials - cotton, silk, wool. But soon it became clear that polymers, fibers and other materials based on them are sometimes better than traditionally used natural materials - they are lighter, stronger, more heat-resistant, and capable of working in aggressive environments. Therefore, chemists and technologists have focused all their efforts on creating new polymers with high performance characteristics and methods for their processing. And we achieved results in this matter that sometimes exceeded the results of similar activities of well-known foreign companies.

Polymers are widely used in many areas of human activity, meeting the needs of various industries, agriculture, medicine, culture and everyday life. At the same time, it is appropriate to note that in last years The function of polymer materials in any industry and the methods for their production have changed somewhat. More and more responsible tasks began to be trusted to polymers. More and more relatively small, but structurally complex and critical parts of machines and mechanisms began to be made from polymers, and at the same time, polymers increasingly began to be used in the manufacture of large-sized body parts of machines and mechanisms that carry significant loads.

The threshold of strength properties of polymer materials was overcome by the transition to composite materials, mainly glass and carbon fiber reinforced plastics. So now the expression “plastic is stronger than steel” sounds quite reasonable. At the same time, polymers have retained their position in the mass production of a huge number of those parts that do not require particularly high strength: plugs, fittings, caps, handles, scales and housings of measuring instruments. Another area specific to polymers, where their advantages over any other materials are most clearly manifested, is the area of ​​interior and exterior finishing.

By the way, the same advantages stimulate the widespread use of polymer materials in the aviation industry. For example, replacing an aluminum alloy with graphite plastic in the manufacture of an aircraft wing slat allows you to reduce the number of parts from 47 to 14, fasteners from 1464 to 8 bolts, reduce weight by 22%, and cost by 25%. At the same time, the safety margin of the product is 178%. Helicopter blades and jet engine fan blades are recommended to be made from polycondensation resins filled with aluminosilicate fibers, which reduces the weight of the aircraft while maintaining strength and reliability.

All these examples show the huge role of polymers in our lives. It is difficult to imagine what materials will be obtained based on them. But we can say with confidence that polymers will occupy, if not the first, then at least one of the first places in production. It is quite obvious that the quality, characteristics and properties of the final products directly depend on the polymer processing technology. The importance of this aspect forces us to look for more and more new processing methods to obtain materials with improved performance. In this abstract, only the basic methods were discussed. Their total number is not limited to this.

BIBLIOGRAPHY

1. Pasynkov V.V., Sorokin V.S., Materials of electronic technology, - M.: Higher School, 1986.

2.A. A. Tager, Physicochemistry of polymers, M., chemistry, 1978.

3. Tretyakov Yu.D., Chemistry: Reference materials. – M.: Education, 1984.

4.Materials Science/Ed. B.N. Arzamasova. – M.: Mechanical Engineering, 1986.

5. Dontsov A. A., Dogadkin B. A., Shershnev V. A., Chemistry of elastomers, - M.: Chemistry, 1981.

Thermoplastics are plastics that, once molded into a product, remain recyclable. They can repeatedly soften when heated and harden when cooled without losing their properties. This is precisely why there is great interest in the recycling of thermoplastic waste, both domestic and industrial.

The composition of municipal solid waste (MSW) in the capital differs markedly from the Russian average. Every year about 110 thousand tons of solid household waste are generated in Moscow. Of these, 8-10% are polymer, and in commercial waste from large enterprises this figure reaches 25%.

Plastic bottles should be highlighted separately in the structure of solid waste. Every year in Moscow alone, about 50 thousand tons of them are thrown away. According to the results of the International Scientific and Practical Conference “Packaging and the Environment”, 30% of all polymer waste are bottles made of polyethylene and polyvinyl chloride. However, at present, according to the State Unitary Enterprise Promotkhody, in Moscow and the region no more than 9 thousand tons of polymer waste separated from solid waste are processed annually. And half of them are in the Moscow region. What are the reasons for such little recycling of thermoplastic waste?

Organizing the collection

Today, several channels for collecting plastic waste are used.

The first and main one is the collection and removal of waste from large shopping complexes. These raw materials are predominantly used packaging and are considered the “cleanest” and best suited for further use.

The second way is selective garbage collection. In the southwest of Moscow, the city administration, together with the State Unitary Enterprise Promotkhody, is conducting such an experiment. Special German Euro containers have been installed in the courtyards of several residential buildings. Container lids with holes: round - for PET bottles, large slot - for paper. Containers are locked and constantly monitored. In two years, 12 tons of plastic bottles were collected. Today the project includes only 19 residential buildings. According to experts, when covering a territory with more than 1 million inhabitants, the benefits of such a system become obvious.

The third option is the sorting of solid waste at specialized enterprises (experimental industrial waste sorting center "Kotlyakovo", private enterprise MSK-1, other waste sorting complexes). It is still quite difficult to accurately determine the volume of sorted waste, but the share of this source of secondary raw materials is already noticeable. Some commercial organizations, under the control of municipal authorities, organize their own collection points for secondary raw materials (including polymer waste) from the population. Primary sorting and pressing usually take place there. However, there are very few such points in the city.

A significant share of secondary raw materials used for processing is collected illegally at landfills. This is done by private companies, and sometimes by the management of the landfills themselves. Collected and sorted materials are sold to resellers or directly to manufacturers.

When processing thermoplastics, the uniformity of the polymers used, the degree of contamination, color and type (film, bottles, scrap), and the form of the supplied waste (compressed, packaging, etc.) are very important. Depending on these and a number of other parameters, the degree of suitability of a particular batch for further processing (and, consequently, its market value) may vary significantly. Waste paper is the most expensive.

Sorting, crushing and compaction can be carried out by numerous intermediaries, waste sorting complexes, processors themselves, and structures of the State Unitary Enterprise "Industrial Waste".

In most cases, manual sorting is used, since the appropriate equipment is expensive and not always effective.

Polymer processing

Collected and sorted waste can be processed into secondary granulate or directly used for the production of new products (shopping bags and packages, disposable tableware, cases for video cassettes, country furniture, polymer pipes, wood-polymer boards, etc.).

Only NII PM OJSC is engaged in the processing of polymer household waste on an industrial scale in Moscow (production of products for the needs of the municipal economy as part of the program for separate waste collection in the South-Western Autonomous District and by order of the capital's mayor's office). State Unitary Enterprise "Promotkhody" carries out crushing, washing and drying, then the flakes at a price of $400 per ton are transported for further processing to the Research Institute of PM.

Other processors of secondary raw materials are either too small (capacity up to 20 tons per month), or under the guise of processing they are engaged in crushing and further resale; at best, they add crushed raw materials to their products. Almost no one is engaged in large-scale production of secondary granulate and agglomerate in Moscow.

According to other information (N.M. Chalaya, NPO "Plastik"), many small companies are engaged in processing polymers contained in Moscow waste, for which this activity is not their main activity. They try not to advertise it, since it is generally accepted that the use of recyclable materials in the production of products worsens its quality.

A typical company for this market is the Vtorpolymer production cooperative, which works directly with the city landfill. The homeless people who live at the landfill collect everything plastic there: bottles, toys, broken buckets, film, etc. For a certain fee, the “product” is handed over to intermediaries, and they deliver it to Vtorpolymer. Here, worn-out items are washed and sent for recycling. They are sorted by color, crushed and added to plastic, which is used to make installation pipes (they are used in the construction of new houses to insulate electrical wiring). The purchase price of dirty plastic scrap is 1 thousand rubles. per ton, clean - 1.5 thousand. Smaller lots are accepted at prices of 1 and 1.5 rubles. per-kg respectively.

Sorting of polymer waste is carried out manually. The main selection criterion is the appearance of the product or the corresponding marking. Without markings, packaging made of polystyrene, polyvinyl chloride or polypropylene cannot be visually distinguished. Bottles are most often considered PET, film - polyethylene (the specific type of PE is usually not determined), although it may well turn out to be PP or PVC. Linoleum is mainly PVC, foamed polystyrene (foam) is easily identified visually, nylon fibers and technical products (spools, bushings) are usually made of polyamide. The probability of matches with this sorting is about 80%.

Analysis of the activities of companies operating in the market recycled materials, allows us to draw the following conclusions:

1) prices of recycled materials on the market are determined by the degree of their preparation for processing. If we take the cost of primary low-density polyethylene granulate as 100%, then the price of pure crushed polyethylene film prepared for processing ranges from 8 to 13% of the cost of the primary polymer. The price of polyethylene agglomerate is from 20 to 30% of the cost of the primary polymer;

2) the price of most granular secondary polymers, averaged by composition, ranges from 45 to 70% of the price of primary polymers;

3) the price of secondary polymers strongly depends on their color, that is, on the quality of preliminary sorting of polymer waste by color. The difference in the price of secondary polymers of pure and mixed colors can reach 10-20%;

4) prices for products made from primary and secondary polymers are, as a rule, almost the same, which makes the use of secondary polymers in production extremely profitable.

On average, the price of polymer waste separated from solid waste, depending on the degree of preparedness, batch and type, ranges from 1 to 8 rubles/kg. Purchase prices from processors depending on the batch and level of contamination are shown in Table 1.

Type of polymer	Price for dirty waste, rub. /kg	Price for clean waste, rub. /kg	Prices for clean waste, $/t (as of April 2002)
Polystyrene
Polyamide
			Table 1

The price of clean MSW waste is usually equal to the price of industrial and commercial waste.

The market price for the purchase by a processor of polymer waste from solid waste consists of the price of purchase by an intermediary from the population (approximately 25% of the cost), fees for the formation of large-scale batches of waste, sorting, pressing and even washing for the most expensive (clean) raw materials.

Prices for products such as agglomerate and granulate average 12-24 rubles/kg (polyamide is more expensive than others - 35-50 rubles/kg, PET - from 20 rubles/kg). Further processing increases the added value depending on the type of product by 30-200 %.

Investment attractiveness

According to most experts, investing in the processing of polymer waste is profitable, but only if supported by government support and legislative framework, focused on the interests of processors of secondary raw materials.

Today, the Moscow market consists of 20-30 small companies engaged in processing polymer waste, mainly of industrial origin. The market as a whole is characterized by informal connections between processors and suppliers, a large share of companies for which this business is a side business, as well as low processing volumes (12-17 thousand tons per year). It can be assumed that if there is a stable demand for such waste from processors, the supply volumes will increase.

It should be noted that the amount of polymer waste that is actually recycled today constitutes a very small part of urban solid waste. And this despite the fact that the demand for polymers and products made from them is constantly increasing, and the problem of waste disposal is increasingly worrying city authorities.

A limiting factor in the construction of new processing plants is the underdevelopment of the waste collection system and the lack of serious suppliers. The coincidence of interests of private business and the state in this area should inevitably lead to the adoption of laws that meet the interests of recyclers.

Present and future

1. The annual volume of PET processing in the capital is 4-5 thousand tons per year. The plans of the Moscow authorities include organizing a system for the selective collection of PET containers by 2003 and creating two production complexes for its processing with a capacity of 3 thousand tons per year. Currently, the construction of two private PET processing plants with a total capacity of six thousand tons annually is being completed.

In the coming months, the Moscow government should adopt regulations regulating the activities of polymer processors (their exact content is not yet known). Existing and under construction capacities are sufficient to meet market needs. The possibility is being considered state support projects of the State Unitary Enterprise "Promotkhody" and the company "Inteko" (potential processing capacity - 7-8 thousand tons per year).

2. The volume of PP recycling in Moscow is 4-5 thousand tons per year, although about 50-60 thousand tons are thrown away annually in the city - mainly film and big bags. After processing, PP in the form of granules is added to primary raw materials or is entirely used for the production of plastic dishes, shopping bags, etc.).

The absence of large-scale projects for the recycling of this polymer (as is the case with PET) opens up wide opportunities for investment. The most profitable at this stage is the processing of recyclable materials into granulate, since in the field of production of consumer goods the competition is much tougher.

3. The volume of PE processing is also 4-5 thousand tons per year. The main type of raw material is film, including agricultural film. In total, about 60-70 thousand tons of polyethylene waste are thrown out in the city every year. As a rule, enterprises processing PE also deal with PP. One of the large companies through which about 2.5 thousand tons per year passes is Plastpoliten.

PE is characterized by high resistance to pollution. However, the existing ban on the use of recycled polymer raw materials in the manufacture of food packaging limits the possibility of sales.

Thus, the most rational option for today seems to be the construction production complex for processing waste polyethylene, polypropylene and PET into granulate.

This production must include:

a) sorting (requires special training of personnel to reduce the proportion of another type of polymer, which is very important for the quality of the product);

b) washing (the largest potential volumes of raw materials are usually not sorted and washed);

c) drying, crushing, agglomeration.

It is economically most profitable to locate this complex in the near Moscow region, since prices for electricity, water, rent of land and industrial space there are significantly lower than in the capital (see Table 2).

Type of polymer	Price for clean waste, $/t	Price for secondary granulate, $/t	Volume in solid waste thousand tons per year
			table 2

For such production to operate effectively, government support is required. It may make sense to partially revise the existing sanitary standards for the processing of solid waste, as well as oblige manufacturers of polymer products to make contributions for the processing of polymer waste. In addition, comprehensive measures should be taken at the level of the Moscow government and individual housing and communal services aimed at developing a selective collection system and creating a network of collection points for recyclable materials.

The state's increased interest in waste disposal is already reflected in the budget: from 2002 to 2010. It is planned to spend 519.2 million rubles for these purposes. from the federal budget. The budgets of the federal subjects are expected to be allocated until 2010. 11.4 billion rubles. for the implementation of the “Diversions” program.

In 2001, Moscow spent 3.1 billion rubles on environmental protection. To date, the cost of already implemented projects for processing household waste is 115.5 million rubles.

Andrey Golinei,

The penetration of polymer materials into a wide variety of applications, including our daily lives, is now taken for granted throughout the world. And this despite the fact that their victorious march began relatively late - in the 1950s, when their production volumes were only about 1 million tons per year. However, with the growth of production and consumption of plastics, the problems of recycling used plastic products have gradually become more acute and have now become extremely urgent. This review discusses the experience of solving these problems in Europe, where Germany is leading in this regard.

Due to their many advantages (in particular, high strength, chemical resistance, the ability to be molded into any shape and any color, low density), they quickly penetrated into all areas of application, including construction, automotive, aerospace, packaging, household products, toys , medical and pharmaceutical products.

Already in 1989, polymer materials overtook such traditional materials as steel in terms of production volumes (we mean volumes, not weight). At that time, their annual production was about 100 million tons. In 2002, the production of polymer materials exceeded the level of 200 million tons, and now almost 300 million tons are produced annually throughout the world. If we consider the issue from a regional perspective, then Over the past decades, there has been a gradual shift in capacity for the production of polymer materials towards the East.

As a result, Asia has now become the most powerful region, where 44% of all world power is concentrated. Polyolefins, the most widely used group of plastics, account for 56% of total production; Polyvinyl chloride ranks second, followed by other traditional polymers such as polystyrene and polyethylene terephthalate (PET). Only 15% of all polymers produced are expensive materials for technical purposes used in special areas. According to forecasts of the European association of polymer producers PlasticsEurope (Brussels), the volume of production of polymeric materials per capita will continue to increase in the future at a rate of about 4% per year. Simultaneously with such success in the market, the volumes of used polymer materials and products increased. If in the period from the 1960s to the 1980s. Although the plastics industry may not have yet paid much attention to the issues of efficient recycling and reuse of used products, these issues later (especially after the German packaging regulation came into force in 1991) became an important topic. At that time, Germany took on the role of pioneer. It became the first country in which standards for the disposal and recycling of polymer waste were developed and implemented on the market. Currently, many other European countries have joined in solving this problem and have developed very successful concepts for the collection and recycling of polymers.

According to the PlasticsEurope association, in 2011, about 27 million tons of polymer materials were used in 27 EU countries, as well as Switzerland and Norway, of which 40% were for short-term use products and 60% for long-term use products. In the same year, about 25 million tons of used polymer materials were collected. Of these, 40% were landfilled, and 60% were sent for recycling. More than 60% of polymer waste came from waste packaging collection systems. In smaller quantities, post-consumer polymer products were sourced from the construction, automotive and electronics sectors.

Exemplary waste collection systems exist in nine European countries– Switzerland, Germany, Austria, Belgium, Sweden, Denmark, Norway, Holland and Luxembourg (listed in descending order). The share of collected used polymer products in these countries ranges from 92 to 99%. In addition, six of the nine countries listed provide the most high level recycling of this waste in Europe: according to this indicator (from 26% to 35% of the volume of collected waste), Norway, Sweden, Germany, Holland, Belgium and Austria are far ahead of other countries. The remaining amount of collected waste is subjected to energy recycling.

One cannot help but rejoice at the fact that over the past five years, not only the amount of waste collected, but also the share of waste recycled has significantly increased. Thanks to this, the volume of waste being disposed of has decreased. Despite this, the polymer materials recycling sector still has enormous potential for further development. To a large extent, this applies to countries with low levels of their recycling.

Experts critically consider the possibilities of energy recycling of polymer materials, namely their combustion, which many consider to be an appropriate way to recycle them. In Germany, 95% of all incinerators are waste recyclers and are therefore approved for energy recovery. Assessing this situation, Michael Scriba, commercial director of mtm plastics (Nidergebra), a company specializing in the processing of polymer materials, notes that from an environmental point of view, the energy recycling of waste is undoubtedly worse than the material one.

Within the plastics industry, recycling has become an important economic sector in recent years. Another important issue hindering the development of the recycling sector in Europe is the export of polymer waste, mainly to Far East. For this reason, there remains a relatively small amount of waste that can be reasonably recycled in Europe; This contributes to a significant increase in competition and higher costs.

Powerful industry supported by associations and companies

Since the 1990s. The intensification of plastic waste recycling in Germany was initiated by several companies and associations that devoted their activities to these problems and are currently actively working on a European scale.

First of all, we are talking about the company Der Gruene Punkt – Duales System Deutschland GmbH (DSD) (Cologne), which was founded in 1990 as the first dual system and today is a leader in offering waste return systems. These include, along with household collection and recycling of commercial packaging, environmentally friendly and cost-effective recycling of plastic elements of electrical appliances and electronic equipment, as well as transport packaging, waste removal from enterprises and organizations, and cleaning of used containers.

In 1992, RIGK GmbH was founded in Wiesbaden as a certified specialist company for servicing companies (bottling, distribution, trading and importing) that own brands, takes back used packaging and freed from product residues from its German partners and sends these packaging for recycling.

An important player in the market is also the company BKV, which was founded in 1993 with the aim of ensuring guaranteed recycling of polymer packaging collected with dual systems. Currently, BKV serves as a kind of base platform for the recycling of polymer materials, dealing with the most significant and pressing problems in this area.

In 1993, another important association was founded - Bundesverband Sekundärrohstoffe und Entsorgung e. V. (bvse) (Bonn), whose origins are associated with the association Altpapierverband e. V. In the polymer materials sector, it provides German companies with professional and politically determined assistance in the collection and recycling of polymer waste. Along with the company BKV, which is part of the association GKV Gesamtverband Kunststoffverarbeitende Industrie e.V. (Bad Homburg), there are other associations and organizations involved in the recycling of polymer materials. These include, inter alia, tecpol Technologieentwicklungs GmbH, which specializes in environmentally efficient recycling of plastic waste, and the specialized compounding and recycling group at TecPart e. V., which is the base association of the GKV association. In 2002, leading German manufacturers of plastic profiles united into the initiative group Rewindo Fenster-RecyclingService GmbH (Bonn). The main goal was to increase the share of dismantled polymer windows, doors and roller shutters that can be recycled (see photo at the title of the article), which would contribute to increasing stability and responsibility in business activities.

It goes without saying that the large plastics recycling industry associations, which have their own working groups for plastics recycling and have successfully proven themselves in practice for decades, such as PlasticsEurope and IK Industrieverband Kunststoffverpackungen e, got involved in solving the problems. V. (Frankfurt).

Successful proven recycling technologies

Precise information on plastic recycling in Germany is provided by analysis results, which are published every two years on behalf of the VDMA member companies and associations - BKV, PlasticsEurope Deutschland e. V., bvse, Fachverband Kunststoff und Gummimaschinen, as well as the union IK. According to these data, in Germany in 2011, about 5 million tons of plastic waste were generated, the largest part (82%) of which was consumer waste. Of the remaining 18%, which is industrial waste, the share of recyclable materials can be up to 90%. As has already been tested in practice, sorted industrial waste can be successfully subjected to in-plant recycling directly at the enterprises where it was generated (photo 1).

In the case of consumer waste, the share of material (that is, without incineration and landfill) recycling is only 30–35%. In this area, there are also already practical methods for recycling waste sorted by type. Examples include the experience of processing polyvinyl chloride (PVC) and PET. As a result of its 10 years of activity, Rewindo, using its own technology for recycling used PVC windows and doors, has gained a strong position in the market.

In recent years, the volume of recycled PVC produced from collected used products by companies specializing in this field Toensmeier Kunststoffe GmbH & Co. KG (Hechter) and Veka Umwelttechnik GmbH (Herselberg-Hainich) was maintained at a level of about 22 thousand tons with an increasing trend.

PET bottles are also collected and recycled after proper sorting. The range of new products made from recycled materials ranges from fibers and films to new bottles. Various companies, such as the Austrian companies Erema GmbH (Ansfelden), Starlinger & Co. GmbH (Vienna) and NGR GmbH (Feldkirchen) have created special production lines for PET recycling. Recently, the European Food Safety Authority EFSA published a positive opinion on the recoSTAR PET iV+ technology for the production of recycled PET suitable for food packaging (developed by Starlinger).

The EFSA opinion serves as the basis for certification of such technologies by the European Commission and member states of the European Union.

To achieve such a result, the interested company must prove that the technology and equipment it has developed for processing polymer waste reduces the degree of contamination of the corresponding PM to a level that is safe for human health.

The standard scenario of the so-called “challenge-test” for the efficiency of cleaning recycled PET, usually obtained from waste in the form of used bottles, involves the use of five control “pollutants” - toluene, chloroform, phenylcyclohexane, benzophenone and lindane, differing in chemical composition , molecular weight and, therefore, migration ability. The tests themselves are carried out in several stages.

First, the recycled PET flakes are washed, after which they are “contaminated” with a control substance with a given concentration (3 ppm) and washed again. Then these re-washed PET flakes are processed using the tested technology into PET regranulate and the residual concentration of the “polluting” medium is determined, from which the degree of purification of recycled PET is calculated. In conclusion, both indicators are compared with the maximum permissible values ​​for them and conclusions are drawn about the effectiveness of cleaning.

In addition to the standard tests, Starlinger independently decided to tighten up the test scenario by conducting them under so-called “worst-case” conditions for the material (Worst-Case-Szenario), in which PET flakes were processed that were not washed after they were contaminated with model environments. Previously, before each type of test - to ensure the purity of the experiment and stable conditions for its conduct - 80-100 kg of transparent virgin PET were processed on the recoSTAR PET 165 iV+ installation (photo 2) in order to clean the working parts of the installation from the remnants of the previous batch of material. The tested PET flakes were colored blue; therefore, the output of PET regranulate from the same installation was only blue in color, indicating that during the processing process it was not mixed with pure PET and the FIFO principle was maintained (first-in, first-out: “first in, first out”). Test results using a standard scenario showed that the recoSTAR PET iV process cleans rPET so effectively that it is well above the EFSA threshold (see table). Even in the case of lindane (a non-volatile non-polar substance), the purification rate was more than 99.9%, although the threshold value is 89.67%. Almost the same results were shown by tests conducted according to the “tightened” scenario, with the exception of benzophenone and lindane. But even in these cases, the degree of PET purification met EFSA requirements. The abbreviated name of the company NGR stands for quite ambitiously - as “Next Generation Recycling Maschinen”. And having become 100% owner of BRITAS Recycling Anlagen GmbH (Hanau, Germany) in May of this year, NGR has significantly strengthened its position in the European and other regional markets of the world. The fact is that BRITAS is known as a developer and manufacturer of filter systems for melts of heavily contaminated polymer materials, including consumer packaging waste (photo 3).

In turn, NGR develops and produces equipment for the recycling of both industrial and consumer polymer waste, having an extensive market for its products.

Both engineering companies are confident in the positive synergistic effect of the merger. The company Gneuss Kunststofftechnik GmbH (Bad Oeynhausen) has achieved great success in the market thanks to its MRS extruder (photo 4), the use of which is even approved by the FDA (Food and Drug Administration) - the US Department of Commerce for food quality control, medicines and cosmetics. In addition, machine manufacturers offer various drying systems, such as the infrared rotary tube from Kreyenborg Plant Technology GmbH (Senden), as well as special filtration systems for PET recycling or crystallization technologies, such as the Crystall-Cut process from Automatik Plastics Machinery (Senden). Grosstheim). Closed loop systems such as the PETcycle system have been successfully used to make new bottles from used bottles.

Summarizing all of the above, it can be stated that the PET recycling system with an annual volume of about 1 million tons is successfully implemented in Europe. A similar situation is observed in the field of processing sorted polyolefin waste, the sorting of which is carried out without any special complications using appropriate separation technologies. In Germany alone, there are ten large and many small preparation plants specializing in the production of recycled granulate suitable for injection molding from household and industrial polyolefin waste. This granulate can be further used for the production of pallets, bathtubs, buckets, pipes and other types of products (photo 5).

Recycling Challenges

Additional challenges for recycling come from polymer products made from several different materials that cannot be separated from each other at a reasonable cost, as well as polymer packaging that cannot be completely emptied. Waste in the form of used consumer film is also problematic for recycling due to significant surface contamination, which requires significant processing costs.

According to Scribe, although there are experienced recycling experts in this area, there are no real markets of European importance. Additional complications also arise when handling the wide variety of PET bottles produced that are not intended for beverages; this significantly limits the volume of their recycling. To date, waste from the automotive and electronics industries has been difficult to recycle.

In such problematic cases, processors and machine builders require special technical solutions (photo 6). In particular, one such solution regarding the recycling of consumer film waste supplied by DSD was recently provided by Herbold Meckesheim GmbH to the waste management company WRZ-Hoerger GmbH & Co. KG (Sontheim). The turnkey production plant, consisting of a system for separating foreign substances, a wet grinding stage and a compaction device, makes it possible to process 7 thousand tons of waste annually into a bulk agglomerate with a high bulk density, suitable for the manufacture of products using injection molding technology (photo 7 ).

In general, the supply program of the Herbold Meckesheim company, which is also known on the Russian market, includes a variety of equipment for processing both heavily contaminated and mixed waste, both solid and hard-to-recycle soft plastic waste - washing plants and dryers, shredders, agglomerators, mills for fine grinding.

The main stated priorities in the development of equipment are its compactness, increased productivity and energy efficiency. At the K-2013 exhibition, the company will demonstrate a number of new products, including:

New mechanical dryer model HVT with a vertical rotor, saving production space, easy to maintain and consuming significantly less energy when drying PET flakes (photo 8);
shredder model SML SB with forced screw feed of waste into the cutting unit, which makes it possible to compact the supplied material and thereby increase processing productivity (Fig. 1);
a machine for grinding large-sized solid waste in the form of, for example, slabs or pipes, which are considered the most difficult objects to process. Especially for the processing of mixed fractions, Erema together with Coperion GmbH & Co. KG (Stuttgart) has developed a combined Corema plant for waste recycling and compounding (photo 9). A characteristic feature of this plant is its suitability for processing a wide range of materials. According to Erema's commercial director Manfred Hackl, we are talking here about an optimal solution for the processing of economically generated mixed waste, in particular for the production of a compound containing 20% ​​talc from waste polypropylene non-woven materials, or for processing waste into in the form of a mixture of PE and PET with additives. Another successful example of several partners joining forces to solve recycling problems is the production line for the recycling of used agricultural films, the recycling of which is difficult and expensive due to their thinness, softness and contamination. The problem was solved by combining in one line a specially optimized grinder model Power Universo 2800 (manufactured by Lindner reSource) and an extrusion plant for recycling polymer materials model 1716 TVEplus manufactured by Erema), which made it possible to obtain high-quality regranulate.

Equipment that is universal in terms of the form of waste processed into regranulate (films, fibers, flakes of PET bottles, waste of foamed polymer materials) is offered by the Austrian company ARTEC Machinery. The impetus for further development and expansion of production capabilities was its 100% entry in 2010 into the “family” group GAW Technology, of which ECON is also a member, complementing the supply program with appropriate extrusion lines for processing crushed waste into regranulate. Due to the design and technological modernization of manufactured equipment over the years, it was possible to increase its productivity by an average of 25%. The modular principle that ARTEC professes when designing its installations allows, as if from cubes, to assemble and install equipment for a specific application, which is currently produced with a capacity of 150 to 1600 kg per hour (Fig. 2).

A specific extrusion plant with an MRS type extruder (see photo 4), designed for processing crushed waste from PA11 polyamide, was also supplied by Gneuss to the British company K2 Polymer.

The source material is obtained by crushing deep-sea oil pipelines, which become unnecessary after the source of oil dries up and must be recovered on land.

The MRS (Multi Rotation System) extruder allows, without the use of chemical cleaning, to provide one-stage purification and processing of these high-quality, but highly contaminated polymer wastes due to many years of contact with oil. This list could be supplemented with many other examples. In conclusion, the recycling sector has become an important area of ​​economic activity in recent years. Although many technologies have already been successfully tested in practice, there remains great potential for further development in the field of recycling. Solution existing problems must begin with the design and manufacture of polymer products that are as recyclable as possible.

Certain opportunities for progress also remain in the development of optimized technological solutions and the creation of appropriate equipment for the processing of complex waste.

To a certain extent, progress in this area can also be facilitated by policy measures that should ensure the wider implementation of optimal waste collection and recycling concepts in each country.

New and proven solutions in the field of recycling of polymer materials will be widely presented from October 16 to 23, 2013 at the International Exhibition “K” in Dusseldorf.

Prepared by Ph.D. V. N. Mymrin
using press materials from the exhibition company Messe Duesseldorf
Recycling of Plastics in Europe:
New and Proven Solutions The penetration of plastics in a v ariety of
applications, including our daily lives, are now seen worldwide as a matter of course. And this
despite the fact that their winning streak started relatively late – 60 years ago, when their output
accounted for only about 1 million tons per year.

However, with the growth of production and consumption of plastics gradually sharpened
and has now become a critical problem disposing of used plastic products. Although many
processes hav e alr eady become established, recycling still has plenty of potential for
improvement. A first step could be the recyclable design of plastics items that should be examined
closely with a view to later r covery. Suitable recycling processes and machine solutions for the
processing of problematical wastes offer a good deal of scope for further dev elopment. This
review discusses the experience of solving these problems in Europe, wher e the leading in this
respect is Germany.

1. INTRODUCTION

One of the most tangible results of anthropogenic activity is the generation of waste, among which plastic waste occupies a special place due to its unique properties.

Plastics are chemical products consisting of high molecular weight, long-chain polymers. The production of plastics at the present stage of development is increasing by an average of 5...6% annually and by 2010, according to forecasts, will reach 250 million tons. Their consumption per capita in industrial developed countries over the past 20 years has doubled, reaching 85...90 kg. By the end of the decade, it is believed that this figure will increase by 45...50%.

THERE ARE ABOUT 150 TYPES OF PLASTICS, 30% OF THEM ARE MIXTURES OF DIFFERENT POLYMERS. TO ACHIEVE CERTAIN PROPERTIES AND BETTER PROCESSING, VARIOUS CHEMICAL ADDITIVES ARE INTRODUCED INTO POLYMERS, WHICH ARE ALREADY MORE THAN 20, AND A NUMBER OF THEM ARE TOXIC MATERIALS. THE PRODUCTION OF ADDITIVES IS CONTINUALLY INCREASING. IF IN 1980 THERE WERE PRODUCED 4000 TONS, THEN BY 2000 THE VOLUME OF PRODUCTION HAS INCREASED TO 7500 TONS, AND ALL OF THEM WILL BE INTRODUCED TO PLASTICS. AND OVER TIME, CONSUMED PLASTICS INEVITABLY TURN INTO WASTE.

ONE OF THE FAST GROWING AREAS OF USING PLASTICS IS PACKAGING.

Of all plastics produced, 41% is used in packaging, of which 47% is spent on food packaging. Convenience and safety, low price and high aesthetics are the determining conditions for the accelerated growth in the use of plastics in the manufacture of packaging.

Such a high popularity of plastics is explained by their lightness, cost-effectiveness and a set of valuable service properties. Plastics are serious competitors to metal, glass, and ceramics. For example, glass bottles require 21% more energy to make than plastic bottles.

But along with this, a problem arises with the disposal of waste, of which there are over 400 different types, resulting from the use of polymer industry products.

Nowadays, more than ever before, the people of our planet are thinking about the enormous pollution of the Earth with continuously increasing plastic waste. In this regard, the textbook replenishes knowledge in the field of recycling and recycling of plastics with the aim of returning them to production and improving the environment in the Russian Federation and in the world.

2 ANALYSIS OF THE STATE OF RECYCLING AND RECYCLING POLYMER MATERIALS

2.1 ANALYSIS OF THE STATE OF RECYCLING POLYMER MATERIALS

Of all plastics produced, 41% is used in packaging, of which 47% is spent on food packaging. Convenience and safety, low price and high aesthetics are the determining conditions for the accelerated growth in the use of plastics in the manufacture of packaging. 40% synthetic polymer packaging household waste, is practically “eternal” - it does not decompose. Therefore, the use of plastic packaging is associated with the generation of waste in the amount of 40...50 kg/year per person.

In Russia, presumably by 2010, polymer waste will amount to more than one million tons, and the percentage of its use is still small. Considering the specific properties of polymer materials - they do not rot or corrode, the problem of their disposal is, first of all, environmental in nature. The total volume of solid waste disposal in Moscow alone is about 4 million tons per year. From general level Only 5...7% of their mass is processed. According to data for 1998, in the average composition of solid household waste delivered for disposal, 8% is plastic, which amounts to 320 thousand tons per year.

However, at present, the problem of recycling waste polymer materials is gaining relevance not only from the standpoint of environmental protection, but is also due to the fact that, in conditions of a shortage of polymer raw materials, plastic waste becomes a powerful raw material and energy resource.

At the same time, resolving issues related to environmental protection requires significant capital investments. The cost of processing and destroying plastic waste is approximately 8 times higher than the cost of processing most industrial waste and almost three times higher than the cost of destroying household waste. This is due to the specific characteristics of plastics, which significantly complicate or make known methods of solid waste disposal unsuitable.

The use of waste polymers allows significant savings in primary raw materials (primarily oil) and electricity.

There are a lot of problems associated with the disposal of polymer waste. They have their own specifics, but they cannot be considered insoluble. However, a solution is impossible without organizing the collection, sorting and primary processing of depreciated materials and products; without developing a price system for secondary raw materials that encourages enterprises to process them; without creating effective methods for processing secondary polymer raw materials, as well as methods for modifying them in order to improve quality; without creating special equipment for its processing; without developing a range of products manufactured from recycled polymer raw materials.

Plastic waste can be divided into 3 groups:

a) technological production waste that arises during the synthesis and processing of thermoplastics. They are divided into irremovable and removable technological waste. Unremovable are edges, cuttings, trimmings, sprues, flash, burrs, etc. In industries involved in the production and processing of plastics, such waste is generated from 5 to 35%. Unremovable waste, essentially representing high-quality raw materials, does not differ in properties from the original virgin polymer. Its processing into products does not require special equipment and is carried out at the same enterprise. Disposable technological production waste is formed when technological regimes are not observed during the synthesis and processing process, i.e. This is a technological defect that can be reduced to a minimum or completely eliminated. Industrial waste is processed into various products, used as an additive to feedstock, etc.;

b) waste from industrial consumption - accumulates as a result of the failure of products made of polymeric materials used in various sectors of the national economy (depreciated tires, containers and packaging, machine parts, agricultural film waste, fertilizer bags, etc.). These wastes are the most homogeneous, least contaminated and therefore are of the greatest interest from the point of view of their recycling;

c) public consumption waste, which accumulates in our homes, in public catering establishments, etc., and then ends up in city landfills; Ultimately, they become a new category of waste – mixed waste.

The greatest difficulties are associated with the processing and use of mixed waste. The reason for this is the incompatibility of thermoplastics included in household waste, which requires their step-by-step separation. In addition, the collection of worn-out polymer products from the population is an extremely complex undertaking from an organizational point of view and has not yet been established in our country.

The bulk of waste is destroyed by burial in the soil or incineration. However, waste destruction is economically unprofitable and technically difficult. In addition, burial, flooding and burning of polymer waste leads to environmental pollution, reduction of land (organization of landfills), etc.

However, both landfilling and incineration continue to be fairly widespread methods of disposing of plastic waste. Most often, the heat released during combustion is used to produce steam and electricity. But the caloric content of the burned raw materials is low, so combustion plants, as a rule, are economically ineffective. In addition, during combustion, soot is formed from incomplete combustion of polymer products, toxic gases are released and, consequently, re-pollution of air and water basins, and rapid wear of furnaces due to severe corrosion.

In the early 1970s. In the last century, work on the creation of bio-, photo- and water-degradable polymers began to develop intensively. The production of degradable polymers caused a real sensation, and this method of destroying failed plastic products was seen as ideal. However, subsequent work in this direction showed that it is difficult to combine high physical and mechanical characteristics, beautiful appearance, ability to quickly degrade, and low cost in products.

In recent years, research into self-destructive polymers has declined significantly, mainly because production costs for such polymers are typically much higher than for conventional plastics, and this destruction method is not economically viable.

The main way of using plastic waste is its recycling, i.e. reuse. It has been shown that capital and operating costs for the main methods of waste disposal do not exceed, and in some cases even lower than, the costs of their destruction. On the positive side recycling is also the fact that an additional amount of useful products is obtained for various sectors of the national economy and there is no re-pollution of the environment. For these reasons, recycling is not only an economically viable but also an environmentally preferable solution to the problem of plastic waste. It is estimated that of the annually generated polymer waste in the form of depreciated products, only a small part (only a few percent) is recycled. The reason for this is the difficulties associated with the preliminary preparation (collection, sorting, separation, cleaning, etc.) of waste, the lack of special equipment for processing, etc.

The main methods of recycling plastic waste include:

1. thermal decomposition by pyrolysis;
2. decomposition to obtain initial low-molecular products (monomers, oligomers);
3. recycling.

Pyrolysis is the thermal decomposition of organic products with or without oxygen. Pyrolysis of polymer waste makes it possible to obtain high-calorie fuel, raw materials and semi-finished products used in various technological processes, as well as monomers used for the synthesis of polymers.

Gaseous products of thermal decomposition of plastics can be used as fuel to produce working water vapor. Liquid products are used to obtain coolants. The range of applications for solid (waxy) products of pyrolysis of plastic waste is quite wide (components of various types of protective compounds, lubricants, emulsions, impregnating materials, etc.)

Catalytic hydrocracking processes have also been developed to convert waste polymers into gasoline and fuel oils.

As a result of the reversibility of the formation reaction, many polymers can decompose again to their original substances. For practical use, methods for splitting PET, polyamides (PA) and polyurethane foams are important. The decomposition products are used again as raw materials for the polycondensation process or as additives to the primary material. However, the impurities present in these products often do not allow the production of high-quality polymer products, for example, fibers, but their purity is sufficient for the production of injection molding compounds, fusible and soluble adhesives.

Hydrolysis is the reverse reaction of polycondensation. With its help, with the directed action of water at the junctions of the components, polycondensates are destroyed to the original compounds. Hydrolysis occurs under extreme temperatures and pressures. The depth of the reaction depends on the pH of the medium and the catalysts used.

This method of using waste is more energy-efficient than pyrolysis, since high-quality chemical products are returned to circulation.

Compared to hydrolysis, another method for breaking down PET waste is more economical - glycolysis. Destruction occurs when high temperatures ah and pressure in the presence of ethylene glycol and with the participation of catalysts to obtain pure diglycol terephthalate. Using this principle, it is also possible to transesterify carbamate groups in polyurethane.

Still the most common thermal method recycling PET waste involves breaking it down with methanol – methanolysis. The process takes place at temperatures above 150°C and a pressure of 1.5 MPa, and is accelerated by transesterification catalysts. This method is very economical. In practice, a combination of glycolysis and methanolysis methods is used.

Currently, the most acceptable for Russia is the recycling of waste polymer materials mechanical recycling, since this processing method does not require expensive special equipment and can be implemented in any place where waste accumulates.

2.2 DISPOSAL OF POLYOLEFIN WASTE

Polyolefins are the most widely used type of thermoplastics. They are widely used in various industries, transport and agriculture. Polyolefins include high and low density polyethylene (HDPE and LDPE), PP. The most effective way to dispose of software waste is to reuse it. The resources of secondary thermoplastics are large: waste from LDPE consumption alone reached 2 million tons in 1995. The use of recycled thermoplastics in general, and PO in particular, allows one to increase the degree of satisfaction in them by 15...20%.

Methods for recycling software waste depend on the brand of polymer and its origin. Technological waste is most easily processed, i.e. production waste that has not been subjected to intense light exposure during operation. Consumption waste made from HDPE and PP also does not require complex methods of preparation, since, on the one hand, products made from these polymers also do not undergo significant impacts due to their design and purpose (thick-walled parts, containers, fittings, etc.), and on the other hand, the original polymers are more resistant to atmospheric factors than LDPE. Such waste only needs to be crushed and granulated before reuse.

2.2.1 Structural and chemical features of recycled polyethylene

The choice of technological parameters for processing waste software and the areas of use of products obtained from them is determined by their physicochemical, mechanical and technological properties, which differ significantly from the same characteristics of the primary polymer. The main features of recycled LDPE (RLDPE), which determine the specifics of its processing, include: low bulk density; features of the rheological behavior of the melt due to the high gel content; increased chemical activity due to changes in structure that occur during the processing of the primary polymer and the use of products obtained from it.

During processing and operation, the material is subjected to mechanochemical influences, thermal, heat and photo-oxidative destruction, which leads to the appearance of active groups, which during subsequent processing are capable of initiating oxidation reactions.

A change in the chemical structure begins already during the primary processing of software, in particular during extrusion, when the polymer is subjected to significant thermal-oxidative and mechanochemical influences. The greatest contribution to changes occurring during operation is made by photochemical processes. These changes are irreversible, while the physical and mechanical properties of, for example, polyethylene film, which has served one or two seasons for covering greenhouses, are almost completely restored after repressing and extrusion.

The formation of a significant number of carbonyl groups in a PE film during its operation leads to an increased ability of HDPE to absorb oxygen, resulting in the formation of vinyl and vinylidene groups in secondary raw materials, which significantly reduce the thermal-oxidative stability of the polymer during subsequent processing and initiate the process of photoaging of such materials and products made from them. , reduce their service life.

The presence of carbonyl groups determines neither the mechanical properties (their introduction up to 9% into the initial macromolecule does not have a significant effect on the mechanical properties of the material), nor the transmission of sunlight by the film (light absorption by carbonyl groups lies in the wavelength region less than 280 nm, and light of this composition practically not contained in the solar spectrum). However, it is the presence of carbonyl groups in PE that determines its very important property - resistance to light.

The initiator of photoaging of PE is hydroperoxides, which are formed during the processing of the primary material in the process of mechanochemical destruction. Their initiating action is especially effective on early stages aging, while carbonyl groups have a significant effect in later stages.

As is known, competing reactions of destruction and structuring occur during aging. The consequence of the first is the formation of low molecular weight products, the second - an insoluble gel fraction. The rate of formation of low molecular weight products is maximum at the beginning of aging. This period is characterized by low gel content and a decrease in physical and mechanical parameters.

Subsequently, the rate of formation of low molecular weight products decreases, a sharp increase in gel content and a decrease in relative elongation are observed, which indicates the occurrence of a structuring process. Then (after reaching a maximum), the gel content in VPE decreases during its photoaging, which coincides with the complete consumption of vinylidene groups in the polymer and the achievement of the maximum permissible values ​​of relative elongation. This effect is explained by the involvement of the resulting spatial structures in the process of destruction, as well as cracking along the boundaries of morphological formations, which leads to a decrease in physical and mechanical characteristics and deterioration of optical properties.

The rate of change in the physical and mechanical characteristics of EPE is practically independent of the content of the gel fraction in it. However, the gel content must always be taken into account as a structural factor when choosing a method of recycling, modification and when determining the areas of use of the polymer.

In table Table 1 shows the characteristics of the properties of LDPE before and after aging for three months and HDPE obtained by extrusion from an aged film.

1 Characteristics of LDPE properties before and after aging

Characteristics		Original	After use	Extrusion
Breaking tensile stress, MPa
Elongation at break, %
Resistance to cracking, h
Lightfastness, days

The nature of the change in physical and mechanical characteristics for LDPE and HDPE is not the same: the primary polymer exhibits a monotonic decrease in both strength and elongation, which amount to 30 and 70%, respectively, after aging for 5 months. For recycled LDPE, the nature of the change in these indicators is somewhat different: the breaking stress practically does not change, and the relative elongation decreases by 90%. The reason for this may be the presence of a gel fraction in HDPE, which acts as an active filler of the polymer matrix. The presence of such a “filler” is the reason for the appearance of significant stresses, which results in an increase in the fragility of the material, a sharp decrease in relative elongation (up to 10% of the values ​​for primary PE), resistance to cracking, tensile strength (10...15 MPa), elasticity, increasing rigidity.

In PE, during aging, not only the accumulation of oxygen-containing groups, including ketones, and low-molecular products, occurs, but also a significant decrease in physical and mechanical characteristics, which are not restored after recycling of the aged polyolefin film. Structural and chemical transformations in HDPE occur mainly in the amorphous phase. This leads to a weakening of the interphase boundary in the polymer, as a result of which the material loses strength, becomes brittle, brittle and subject to further aging both during recycling into products and during operation of such products that are characterized by low physical and mechanical properties and service life.

To assess the optimal processing modes of recycled polyethylene raw materials, its rheological characteristics are of great importance. HDPE is characterized by low fluidity at low shear stresses, which increases with increasing stress, and the increase in fluidity for HPPE is greater than for primary one. The reason for this is the presence of a gel in HDPE, which significantly increases the activation energy of the viscous flow of the polymer. The fluidity can be adjusted by also changing the temperature during processing - with increasing temperature, the fluidity of the melt increases.

So, material is received for recycling, the background of which has a very significant impact on its physical, mechanical and technological properties. During recycling, the polymer is subjected to additional mechanochemical and thermal-oxidative effects, and the change in its properties depends on the frequency of processing.

When studying the influence of the frequency of processing on the properties of the resulting products, it was shown that 3–5 times of processing has an insignificant effect (much less than primary processing). A noticeable decrease in strength begins after 5–10 fold processing. In the process of repeated processing of HDPE, it is recommended to increase the casting temperature by 3...5% or the screw speed during extrusion by 4...6% to destroy the resulting gel. It should be noted that during recycling, especially when exposed to atmospheric oxygen, the molecular weight of polyolefins decreases, which leads to a rapid increase in the fragility of the material. Repeated processing of another polymer from the class of polyolefins, PP, usually leads to an increase in the melt flow index (MFR), although the strength characteristics of the material do not undergo significant changes. Therefore, the waste generated during the manufacture of parts from PP, as well as the parts themselves at the end of their service life, can be reused in a mixture with the source material to produce new parts.

From all of the above, it follows that secondary raw materials should be modified in order to improve the quality and increase the service life of products made from it.

2.2.2 Technology for processing recycled polyolefin raw materials into granulate

To transform waste thermoplastics into raw materials suitable for subsequent processing into products, its pre-treatment is necessary. The choice of pretreatment method depends mainly on the source of waste generation and the degree of its contamination. Thus, homogeneous waste from the production and processing of LDPE is usually processed at the site of its generation, which requires minor pre-treatment - mainly grinding and granulation.

Waste in the form of disused products requires more thorough preparation. Pre-treatment of waste agricultural PE film, fertilizer bags, waste from other compact sources, as well as mixed waste includes the following steps: sorting (rough) and identification (for mixed waste), crushing, separation of mixed waste, washing, drying. After this, the material is subjected to granulation.

Preliminary sorting involves rough separation of waste according to various characteristics: color, size, shape and, if necessary and possible, by type of plastic. Preliminary sorting is usually done manually on tables or conveyor belts; during sorting, various foreign objects and inclusions are simultaneously removed from the waste.

The separation of mixed (household) thermoplastic waste by type is carried out using the following main methods: flotation, separation in heavy media, aeroseparation, electrical separation, chemical methods and deep cooling methods. The most widely used method is flotation, which allows the separation of mixtures of industrial thermoplastics such as PE, PP, PS and PVC. Plastics are separated by adding surfactants to water, which selectively change their hydrophilic properties.

In some cases, an effective way to separate polymers may be to dissolve them in a common solvent or in a mixture of solvents. By treating the solution with steam, PVC, PS and a mixture of polyolefins are isolated; product purity is at least 96%.

Flotation and separation methods in heavy media are the most effective and cost-effective of all those listed above.

Out-of-use waste containing foreign impurities of no more than 5% from the raw material warehouse is delivered to the waste sorting unit 1 , during which random foreign inclusions are removed from them and heavily contaminated pieces are discarded. Waste that has been sorted is crushed in knife crushers 2 wet or dry grinding to obtain a loose mass with a particle size of 2...9 mm.

The performance of a shredding device is determined not only by its design, the number and length of knives, rotor speed, but also by the type of waste. Thus, the lowest productivity is when processing foam plastic waste, which takes up a very large volume and is difficult to load compactly. Higher productivity is achieved when processing waste films, fibers, and blown products.

For all knife crushers characteristic feature is increased noise, which is associated with the specifics of the process of grinding secondary polymer materials. To reduce the noise level, the chopper, together with the motor and fan, is enclosed in a noise-proof casing, which can be detachable and have special windows with dampers for loading the crushed material.

Grinding is a very important stage in preparing waste for processing, since the degree of grinding determines the bulk density, flowability and particle size of the resulting product. Regulating the degree of grinding makes it possible to mechanize the processing process, improve the quality of the material by averaging its technological characteristics, reduce the duration of other technological operations, and simplify the design of processing equipment.

A very promising method of grinding is cryogenic, which makes it possible to obtain powders from waste with a degree of dispersion of 0.5...2 mm. The use of powder technology has a number of advantages: reduced mixing time; reduction of energy consumption and working time for routine maintenance of mixers; better distribution of components in the mixture; reducing the destruction of macromolecules, etc.

Of the known methods for producing powdered polymer materials used in chemical technology, the most suitable method for grinding thermoplastic waste is mechanical grinding. Mechanical grinding can be carried out in two ways: cryogenically (grinding in an environment of liquid nitrogen or other refrigerant and at ordinary temperatures in an environment of disagglomerating ingredients, which are less energy-intensive.

Next, the crushed waste is fed into a washing machine for washing. 3 . Washing is carried out in several stages using special washing mixtures. Centrifuged 4 the mass with a moisture content of 10...15% is fed to a drying unit for final dewatering 5 , to a residual moisture content of 0.2%, and then into granulator 6 (Fig. 1.1).

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Rice. 1.1 Scheme for recycling polyolefins into granules:

1 – waste sorting unit; 2 – crusher; 3 – washing machine; 4 – centrifuge; 5 – drying unit; 6 – granulator

Dryers are used to dry waste various types: shelf, belt, bucket, fluidized bed, vortex, etc.

Installations are produced abroad that have devices for both washing and drying with a capacity of up to 350...500 kg/h. In such an installation, crushed waste is loaded into a bath, which is filled with a cleaning solution. The film is mixed with a paddle mixer, while the dirt settles to the bottom, and the washed film floats to the surface. Dehydration and drying of the film is carried out on a vibrating sieve and in a vortex separator. Residual moisture is less than 0.1%.

Granulation is the final stage of preparation of secondary raw materials for subsequent processing into products. This stage is especially important for HDPE due to its low bulk density and difficulty of transportation. During the granulation process, the material is compacted, its further processing is facilitated, the characteristics of secondary raw materials are averaged, resulting in a material that can be processed using standard equipment.

For the plasticization of crushed and purified software waste, single-screw extruders with a length of (25...30) are most widely used. D, equipped with a continuous filter and having a degassing zone. Such extruders quite effectively process almost all types of secondary thermoplastics with a bulk density of crushed material ranging from 50...300 kg/m3. However, for processing contaminated and mixed waste, worm presses of special designs are needed, with short multi-thread worms (length (3.5...5) D), having a cylindrical nozzle in the extrusion zone.

The main unit of this system is an extruder with a drive power of 90 kW, a screw diameter of 253 mm and a ratio L/D= 3.75. At the exit of the extruder, a corrugated nozzle with a diameter of 420 mm is designed. Due to the release of heat during friction and shear effects on the polymer material, it melts in a short period of time, and rapid homogenization is ensured

melt. By changing the gap between the cone nozzle and the casing, you can adjust the shear force and friction force, while changing the processing mode. Since melting occurs very quickly, thermal degradation of the polymer is not observed. The system is equipped with a degassing unit, which is a necessary condition for processing recycled polymer raw materials.

Depending on the sequence of cutting and cooling processes, secondary granular materials are produced in two ways: die granulation and underwater granulation. The choice of granulation method depends on the properties of the thermoplastic being processed and, especially, on the viscosity of its melt and adhesion to the metal.

During granulation on the head, the polymer melt is squeezed out through a hole in the form of cylindrical strands, which are cut off by knives sliding along the spinneret plate. The resulting granules are discarded from the head with a knife and cooled. Cutting and cooling can be done in air, in water, or by cutting in air and cooling in water. For software that has high adhesion to metal and an increased tendency to stick together, water is used as a cooling medium.

When using equipment with a large unit power, so-called underwater granulation is used. With this method, the polymer melt is extruded in the form of strands through the holes of the die plate on the head directly into the water and cut into granules by rotating knives. The cooling water temperature is maintained within 50...70 °C, which promotes more intense evaporation of residual moisture from the surface of the granules; the amount of water is 20...40 m3 per 1 ton of granulate.

Most often, strands or ribbons are formed in the head of granulators, which are granulated after cooling in a water bath. The diameter of the resulting granules is 2…5 mm.

Cooling should be carried out at optimal conditions so that the granules do not deform, do not stick together, and ensure the removal of residual moisture.

The temperature of the head has a significant influence on the size distribution of granules. To ensure uniform melt temperature, gratings are placed between the extruder and the outlet openings of the head. The number of outlet holes in the head is 20...300.

The performance of the granulation process depends on the type of recycled thermoplastic and its rheological characteristics.

Studies of VPE granulate indicate that its viscous-flow properties are practically no different from the properties of primary PE, i.e. it can be processed using the same extrusion and injection molding processes as virgin PE. However, the resulting products are characterized by low quality and durability.

Granulates are used to produce packaging for household chemicals, hangers, construction parts, agricultural implements, pallets for transporting goods, exhaust pipes, lining of drainage channels, free-flow pipes for land reclamation and other products. These products are made from “pure” recycled materials. However, more promising is the addition of secondary raw materials to primary ones in an amount of 20...30%. The introduction of plasticizers, stabilizers, and fillers into the polymer composition makes it possible to increase this figure to 40...50%. This increases the physical and mechanical characteristics of products, but their durability (when used in harsh climatic conditions) is only 0.6...0.75 of the durability of products made from primary polymer. A more effective way is to modify secondary polymers, as well as create highly filled secondary polymer materials.

2.2.3 Methods for modifying secondary polyolefins

The results of a study of the mechanism of processes occurring during the operation and processing of software and their quantitative description allow us to conclude that intermediate products obtained from secondary raw materials should contain no more than 0.1...0.5 mol of oxidized active groups and have optimal molecular weight and MWD , and also have reproducible physical, mechanical and technological indicators. Only in this case can the semi-product be used for the production of products with a guaranteed service life instead of scarce primary raw materials. However, the currently produced granulate does not meet these requirements.

A reliable way to solve the problem of creating high-quality polymer materials and products from recycled materials is to modify the granulate, the purpose of which is to shield functional groups and active centers by chemical or physicochemical methods and create a material that is homogeneous in structure with reproducible properties.

Methods for modifying secondary raw materials can be divided into chemical (cross-linking, introduction of various additives, mainly of organic origin, treatment with organosilicon liquids, etc.) and physical-mechanical (filling with mineral and organic fillers).

For example, the maximum content of the gel fraction (up to 80%) and the highest physical and mechanical properties of cross-linked HDPE are achieved by introducing 2...2.5% dicumyl peroxide on rollers at 130 °C for 10 minutes. The relative elongation at break of such a material is 210%, the melt flow rate is 0.1...0.3 g/10 min. The degree of cross-linking decreases with increasing temperature and increasing duration of rolling as a result of the competing process of destruction. This allows you to adjust the degree of crosslinking, physical, mechanical and technological characteristics of the modified material.

A method for molding products from HDPE has been developed by introducing dicumyl peroxide directly during the processing process, and prototypes of pipes and injection molded products containing 70...80% of the gel fraction have been obtained.

The introduction of wax and elastoplast (up to 5 parts by weight) significantly improves the processability of EPE, increases the physical and mechanical properties (especially elongation at break and resistance to cracking - by 10% and from 1 to 320 hours, respectively) and reduces their scatter, which indicates an increase in the homogeneity of the material.

Modification of HDPE with maleic anhydride in a disk extruder also leads to an increase in its strength, heat resistance, adhesive ability and resistance to photoaging. In this case, the modifying effect is achieved with a lower concentration of the modifier and a shorter duration of the process than with the introduction of elastoplast.

A promising way to improve the quality of polymer materials from recycled materials is thermomechanical treatment with organosilicon compounds. This method makes it possible to obtain products from recycled materials with increased strength, elasticity and resistance to aging. The modification mechanism consists in the formation of chemical bonds between the siloxane groups of the organosilicon liquid and the unsaturated bonds and oxygen-containing groups of secondary PO.

The technological process for producing modified material includes the following stages: sorting, crushing and washing of waste; waste treatment with organosilicon liquid at 90 ± 10 °C for 4…6 hours; drying of modified waste by centrifugation; re-granulation of modified waste.

In addition to the solid-phase modification method, a method for modifying VPE in solution has been proposed, which makes it possible to obtain HPPE powder with a particle size of no more than 20 μm. This powder can be used for processing into products by rotational molding and for coating by electrostatic spraying.

The creation of filled polymer materials based on recycled polyethylene raw materials is of great scientific and practical interest. The use of polymer materials from recycled materials containing up to 30% filler will allow the release of up to 40% of primary raw materials and use it for the production of products that cannot be obtained from recycled materials (pressure pipes, packaging films, reusable transport containers, etc.). This will significantly reduce the shortage of primary polymer raw materials.

To obtain filled polymer materials from recycled materials, you can use dispersed and reinforcing fillers of mineral and organic origin, as well as fillers that can be obtained from polymer waste (crushed thermoset waste and crumb rubber). Almost all thermoplastic waste can be filled, as well as mixed waste, which is preferable to use for this purpose from an economic point of view.

For example, the feasibility of using lignin is associated with the presence of phenolic compounds, contributing to the stabilization of VPEN during operation; mica - with the production of products with low creep, increased heat and weather resistance, and also characterized by low wear of processing equipment and low cost. Kaolin, shell rock, oil shale ash, coal spheres and iron are used as cheap inert fillers.

When finely dispersed phosphogypsum, granulated in polyethylene wax, is introduced into VPE, compositions with increased elongation at break are obtained. This effect can be explained by the plasticizing effect of polyethylene wax. Thus, the tensile strength of PE filled with phosphogypsum is 25% higher than that of PE, and the tensile modulus is 250% higher.

The reinforcing effect when mica is introduced into EPE is associated with the peculiarities of the crystalline structure of the filler, the high characteristic ratio (ratio of flake diameter to thickness), and the use of crushed, powdered EPE made it possible to preserve the structure of the flakes with minimal destruction.

Compositions containing lignin, shale, kaolin, spheres, sapropel waste have relatively low physical and mechanical properties, but they are the cheapest and can be used in the production of construction products.

2.3 RECYCLING OF POLYVINYL CHLORIDE

During processing, polymers are exposed to high temperatures, shear stresses and oxidation, which leads to changes in the structure of the material, its technological and operational properties. Thermal and thermo-oxidative processes have a decisive influence on changes in the structure of the material.

PVC is one of the least stable carbon-chain industrial polymers. The destruction reaction of PVC – dehydrochlorination – begins already at temperatures above 100 °C, and at 160 °C the reaction proceeds very quickly. As a result of thermal oxidation of PVC, aggregative and disaggregative processes occur - cross-linking and destruction.

The destruction of PVC is accompanied by a change in the initial color of the polymer due to the formation of chromophore groups and a significant deterioration in physical, mechanical, dielectric and other performance characteristics. As a result of cross-linking, linear macromolecules are transformed into branched and, ultimately, cross-linked three-dimensional structures; at the same time, the solubility of the polymer and its ability to be processed significantly deteriorate. In the case of plasticized PVC, cross-linking reduces the compatibility of the plasticizer with the polymer, increases the migration of the plasticizer and irreversibly degrades the performance properties of the materials.

Along with taking into account the influence of operating conditions and the frequency of processing of secondary polymer materials, it is necessary to evaluate the rational ratio of waste and fresh raw materials in the composition intended for processing.

When extruding products from mixed raw materials, there is a risk of defects due to different viscosities of the melts, so it is proposed to extrude primary and secondary PVC on different machines, but powdered PVC can almost always be mixed with a secondary polymer.

An important characteristic that determines the fundamental possibility of recycling PVC waste (permissible processing time, service life of a secondary material or product), as well as the need for additional strengthening of the stabilizing group, is the thermal stability time.

2.3.1 Methods for preparing polyvinyl chloride waste

Homogeneous industrial waste, as a rule, is recycled, and in cases where only thin layers of material are subjected to deep aging.

In some cases, it is recommended to use an abrasive tool to remove the destroyed layer with subsequent processing of the material into products that are not inferior in properties to products obtained from the original materials.

To separate the polymer from the metal (wires, cables), a pneumatic method is used. Generally, separated plasticized PVC can be used as insulation for low voltage wires or for injection molding. To remove metal and mineral inclusions, the experience of the flour milling industry can be used, based on the use of an induction method, a method of separation based on magnetic properties. To separate aluminum foil from thermoplastic, heating in water at 95...100 °C is used.

It is proposed to immerse unusable containers with labels in liquid nitrogen or oxygen at a temperature not exceeding –50 ° C to make the labels or adhesive brittle, which will then make them easy to crush and separate homogeneous material, such as paper.

An energy-efficient method of dry preparation of plastic waste using a compactor. The method is recommended for processing waste artificial leather (IL), PVC linoleum and includes a number of technological operations: grinding, separation of textile fibers, plasticization, homogenization, compaction and granulation; Supplements can also be added. The lining fibers are separated three times - after the first knife crushing, after compaction and secondary knife crushing. A molding mass is obtained that can be processed by injection molding, also containing fibrous components that do not interfere with processing, but serve as a filler that strengthens the material.

2.3.2 Methods for recycling polyvinyl chloride plastic waste

Injection molding

The main types of waste based on unfilled PVC are ungelatinized plastisol, process waste and defective products. Russian light industry enterprises use the following technology for processing plastisol waste using injection molding methods.

It has been established that products from recycled PVC materials of satisfactory quality can be obtained using plastisol technology. The process includes grinding waste films and sheets, preparing PVC paste in a plasticizer, and molding a new product by casting.

When cleaning the dispenser and mixer, ungelatinized plastisol was collected in containers, subjected to gelatinization, then mixed with process waste and defective products on rollers, the resulting sheets were processed using rotary grinders. The plastisol chips thus obtained were processed by injection molding. Plastisol crumbs in an amount of 10...50 wt. h can be used in composition with rubber to produce rubber mixtures, and this makes it possible to exclude softeners from the formulations.

To process waste by injection molding, as a rule, machines are used that operate according to the intrusion type, with a constantly rotating screw, the design of which ensures spontaneous capture and homogenization of waste.

One of the promising methods of use PVC waste is a multi-component casting. With this processing method, the product has outer and inner layers made of different materials. The outer layer is, as a rule, high-quality commercial plastics, stabilized, painted, and having a good appearance. The inner layer is recycled polyvinyl chloride raw material. Processing thermoplastics using this method makes it possible to significantly save scarce primary raw materials, reducing its consumption by more than half.

Extrusion

Currently, one of the most effective methods for processing waste PVC-based polymer materials for the purpose of their disposal is the method of elastic-strain dispersion, based on the phenomenon of multiple destruction under conditions of combined influence on the material high pressure and shear deformation at elevated temperatures.

Elastic-strain dispersion of pre-coarsely crushed materials with a particle size of 103 microns is carried out in a single-screw rotary disperser. Used waste of plasticized duplicated film materials on various bases (linoleum on a polyester fabric base, foam film on a paper base, artificial leather on a cotton fabric base) is processed into dispersed homogeneous secondary material, which is a mixture of PVC plastics with a crushed base with the most probable particle size 320...615 microns, predominantly asymmetrical in shape, with a high specific surface area (2.8...4.1 m2/g). Optimal conditions dispersion, in which the most highly dispersed product is formed - the temperature in the dispersant zones is 130...150...70 °C; load level no more than 60%; minimum screw rotation speed 35 rpm. An increase in the processing temperature of PVC materials leads to an undesirable intensification of destructive processes in the polymer, which is expressed in darkening of the product. Increasing the loading rate and screw rotation speed worsens the dispersion of the material.

Processing of waste baseless plasticized PVC materials (agricultural film, insulating film, PVC hoses) by the method of elastic-strain dispersion to obtain high-quality highly dispersed secondary material can be carried out without technological difficulties with a wider variation of dispersion modes. A more finely dispersed product with a particle size of 240...335 microns, predominantly spherical in shape, is formed.

Elastic-deformation effects when dispersing rigid PVC materials (impact-resistant material for mineral water bottles, PVC plumbing pipes, etc.) must be carried out at higher temperatures (170...180...70 °C), loading degree no more than 40% and minimum screw rotation speed 35 rpm. When deviating from the specified dispersion modes, technological difficulties and deterioration in the quality of the resulting secondary product in terms of dispersion are observed.

In the process of processing waste PVC materials, simultaneously with dispersion, it is possible to modify the polymer material by introducing 1...3 wt. into the feedstock. h metal-containing heat stabilizers and 10...30 wt. h plasticizers. This leads to an increase in the thermal stability margin when using metal stearates by 15...50 minutes and an improvement in the flow rate of the melt processed together with ester plasticizers of the material by 20...35%, as well as an improvement in the manufacturability of the dispersion process.

The resulting secondary PVC materials, due to their high dispersion and developed particle surface, have surface activity. This property of the resulting powders predetermined their very good compatibility with other materials, which allows them to be used to replace (up to 45% by weight) the starting raw materials when producing the same or new polymer materials.

Twin screw extruders can also be used to process PVC waste. They achieve excellent homogenization of the mixture, and the plasticization process is carried out under milder conditions. Since twin-screw extruders operate on the displacement principle, the residence time of the polymer in them at the plasticization temperature is clearly defined and its delay in the high-temperature zone is eliminated. This prevents overheating and thermal destruction of the material. The uniform flow of the polymer through the cylinder provides good conditions for degassing in the low-pressure zone, which allows the removal of moisture, products of destruction and oxidation, and other volatiles usually contained in waste.

To process polymer composite materials, including IR, cable insulation waste, paper-based thermoplastic coatings and others, methods based on a combination of extrusion preparation and compression molding can be used. To implement this method, a unit consisting of two machines is proposed, each of which injects 10 kg. The proportion of non-polymeric materials specially introduced into waste can be up to 25%, and even the copper content can reach 10%.

The method of co-extrusion of fresh thermoplastic, which forms the wall layers, and polymer waste, which makes up the inner layer, is also used, as a result a three-layer product (for example, a film) can be obtained. Another method, blow molding, is proposed in. In the developed design of the extrusion blow molding plant, a screw-disk extruder with a blow-blow drive is provided as a melt generator. Extrusion blow molding is used to make bottles, containers and other hollow products from a mixture of primary and recycled PVC.

Calendering

An example of waste processing using the calendering method is the so-called “Regal” process, which consists of calendering the material and producing plates and sheets that are used for the production of containers and furniture. The convenience of this process for processing waste of various compositions lies in the ease of its adjustment by changing the gap between the calender rolls to achieve a good shear and dispersive effect on the material. Good plasticization and homogenization of the material during processing ensures the production of products with sufficiently high strength characteristics. The method is economically beneficial for thermoplastics that are plasticized at relatively low temperatures, basically, it is soft PVC.

For the preparation of IR and lenoleum waste, a unit has been developed, consisting of a knife crusher, a mixing drum and three-roll refining rollers. As a result of high friction, high pressing pressure and mixing between rotating surfaces, the components of the mixture are further crushed, plasticized and homogenized. In just one pass through the machine, the material acquires fairly good quality.

Pressing

One of the traditional methods for processing waste polymer materials is pressing; in particular, the most common method can be called the “Regal-Converter” method. Grinding waste of uniform thickness on a conveyor belt is fed into the oven and melted. The mass thus plasticized is then compressed. The proposed method is used to process plastic mixtures containing more than 50% foreign substances.

There is a continuous process for recycling waste synthetic carpets and IR. Its essence is as follows: the ground waste is fed into a mixer, where 10% of the binding material, pigments, and fillers (for strengthening) are added. This mixture is pressed into plates in a two-belt press. The plates have a thickness of 8...50 mm with a density of about 650 kg/m3. Due to their porosity, the plates have heat and sound insulation properties. They are used in mechanical engineering and the automotive industry as structural elements. With one- or two-sided lamination, these plates can be used in the furniture industry. In the USA, the pressing process is used to make heavy weight plates.

Another technological method is also used, based on foaming in a mold. The developed options differ in the methods of introducing pore-forming agents into secondary raw materials and the supply of heat. Blowing agents can be introduced in a closed mixer or extruder. However, the mold foaming method is more productive, when the pore formation process is carried out in a press.

A significant disadvantage of the method of press sintering of polymer waste is poor mixing of the mixture components, which leads to a decrease in the mechanical properties of the resulting materials.

The problem of recycling waste PVC plastics is currently being intensively developed, but there are many difficulties associated primarily with the presence of filler. Some developers have taken the path of isolating the polymer from the composite and then using it. However, these technological options are often uneconomical, labor-intensive and suitable for a narrow range of materials.

Known methods of direct thermoforming either require high additional costs (preparatory operations, addition of primary polymer, plasticizers, use of special equipment), or do not allow the processing of highly filled waste, in particular, PVC plastics.

2.4 DISPOSAL OF WASTE POLYSTYRENE PLASTICS

Polystyrene waste accumulates in the form of disused products made from PS and its copolymers (bread bins, vases, cheese bowls, various dishes, grates, jars, hangers, facing sheets, parts of commercial and laboratory equipment etc.), as well as in the form of industrial (technological) waste of general purpose PS, impact-resistant PS (HIPS) and its copolymers.

Recycling of polystyrene plastics can be done in the following ways:

1. disposal of heavily contaminated industrial waste;
2. recycling of technological waste of UPS and ABS plastic using injection molding, extrusion and pressing methods;
3. recycling of worn-out products;
4. recycling of waste polystyrene foam (EPS);
5. disposal of mixed waste.

Heavily contaminated industrial waste is generated in the production of PS and polystyrene plastics during cleaning of reactors, extruders and production lines in the form of pieces of various sizes and shapes. Due to contamination, heterogeneity and poor quality, this waste is mainly destroyed by incineration. It is possible to utilize them by destruction, using the resulting liquid products as fuel.

The possibility of attaching ionogenic groups to the benzene ring of polystyrene makes it possible to obtain ion exchangers based on it. The solubility of the polymer also does not change during processing and operation. Therefore, to obtain mechanically strong ion exchangers, it is possible to use technological waste and worn-out polystyrene products, the molecular weight of which is brought by thermal destruction to the values ​​​​required by the conditions for the synthesis of ion exchangers (40...50 thousand). Subsequent chloromethylation of the resulting products leads to the production of compounds soluble in water, which indicates the possibility of using recycled polystyrene raw materials to obtain soluble polyelectrolytes.

Technological waste of PS (as well as software) in its physical, mechanical and technological properties does not differ from primary raw materials. These wastes are returnable and mostly

are used at the enterprises where they are formed. They can be added to the primary PS or used as independent raw materials in the production of various products.

A significant amount of technological waste (up to 50%) is generated during the processing of polystyrene plastics by injection molding, extrusion and vacuum molding, the return of which to processing processes can significantly increase the efficiency of the use of polymer materials and create waste-free production in the plastics processing industry.

ABS plastics are widely used in the automotive industry for the manufacture of large car parts, in the production of plumbing fixtures, pipes, consumer goods, etc.

Due to the increasing consumption of styrene plastics, the amount of waste is also growing, the use of which is economically and environmentally feasible, taking into account the increasing cost of raw materials and the decrease in their resources. In many cases, recycled materials can be used to replace virgin materials.

It has been established that during repeated processing of an ABS polymer, two competing processes occur in it: on the one hand, partial destruction of macromolecules, on the other, partial intermolecular cross-linking, which increase as the number of processing cycles increases.

When choosing a method for processing extruded ABS, the fundamental possibility of molding products using direct pressing, extrusion, and injection molding has been proven.

An effective technological stage for processing ABS waste is drying the polymer, which makes it possible to bring the moisture content in it to a level not exceeding 0.1%. In this case, the formation of such defects in the material that arise from excess moisture, such as a scaly surface, silveriness, and delamination of products along the thickness, is eliminated; Pre-drying improves the properties of the material by 20...40%.

However, the direct pressing method turns out to be ineffective, and the extrusion of the polymer is difficult due to its high viscosity.

Recycling technological waste from ABS polymer using injection molding seems promising. In this case, to improve the fluidity of the polymer, it is necessary to introduce technological additives. An additive to the polymer facilitates the processing of ABS polymer, as it leads to an increase in the mobility of macromolecules, the flexibility of the polymer and a decrease in its viscosity.

Products obtained using this method are not inferior in performance to products made from primary polymer, and sometimes even surpass them.

Defective and worn-out products can be disposed of by grinding, followed by molding the resulting crumbs in a mixture with primary materials or as an independent raw material.

A much more complex situation is observed in the area of ​​recycling of worn-out PS products, including foam plastics. Abroad, the main ways of their disposal are pyrolysis, combustion, photo- or biodegradation, and burial. Depreciated products for cultural and household purposes, as well as for the industry of polymer, construction, thermal insulation materials and others can be recycled into products. This mainly applies to products made from impact-resistant PS.

Before recycling, block PS must be combined with impact-resistant PS (in a 70:30 ratio), modified in other ways, or subjected to recycling of its copolymer with acrylonitrile, methyl methacrylate (MS), or ternary copolymers with MC and acrylonitrile (MCN). Copolymers MC and MSN are characterized by higher resistance to atmospheric aging (compared to impact-resistant compositions), which is of great importance for subsequent processing. Secondary PS can be added to PE.

To convert waste polystyrene films into secondary polymer raw materials, they are subjected to agglomeration in rotary agglomerators. The low impact strength of PS causes rapid grinding (compared to other thermoplastics). However, the high adhesive ability of PS leads, firstly, to the adhesion of material particles and the formation of large aggregates before (80 °C) the material becomes plastic (130 °C), and, secondly, to the adhesion of the material to processing equipment. This makes the agglomeration of PS significantly more difficult compared to PE, PP and PVC.

Waste EPS can be dissolved in styrene and then polymerized in a mixture containing ground rubber and other additives. The copolymers obtained in this way are characterized by fairly high impact strength.

Currently, the recycling industry faces the challenge of processing mixed plastic waste. Mixed waste processing technology includes sorting, grinding, washing, drying and homogenization. Recycled PS obtained from mixed waste has high physical and mechanical properties; it can be added to asphalt and bitumen in a molten state. At the same time, their cost is reduced and strength characteristics increase by approximately 20%.

To improve the quality of recycled polystyrene raw materials, they are modified. This requires studies of its properties during thermal aging and operation. The aging of PS plastics has its own specifics, which is clearly manifested especially for impact-resistant materials that, in addition to PS, contain rubber.

During heat treatment of PS materials (at 100...200 °C), its oxidation occurs through the formation of hydroperoxide groups, the concentration of which quickly increases in the initial stage of oxidation, followed by the formation of carbonyl and hydroxyl groups.

Hydroperoxide groups initiate photo-oxidation processes that occur during the operation of PS products under conditions of exposure to solar radiation. Photodestruction is also initiated by unsaturated groups contained in rubber. A consequence of the combined influence of hydroperoxide and unsaturated groups in the early stages of oxidation and carbonyl groups in later stages is lower resistance to photo-oxidative destruction of products made from PS compared to PO. The presence of unsaturated bonds in the rubber component of the UPS when heated leads to auto-acceleration of the destruction process.

During photoaging of rubber-modified PS, chain scission prevails over the formation of cross-links, especially with a high content of double bonds, which has a significant impact on the morphology of the polymer, its physicomechanical and rheological properties.

All these factors must be taken into account when recycling PS and UPS products.

2.5 RECYCLING POLYAMIDE WASTE

A significant place among solid polymer waste is occupied by polyamide waste, which is generated mainly during the production and processing of fiber products (nylon and anide), as well as obsolete products. The amount of waste during the production and processing of fiber reaches 15% (of which during production - 11...13%). Since PA is an expensive material with a number of valuable chemical and physical-mechanical properties, the rational use of its waste is of particular importance.

The variety of types of secondary PA requires the creation of special processing methods and at the same time opens up wide opportunities for their selection.

PA-6.6 waste has the most stable characteristics, which is a prerequisite for the creation of universal methods for their processing. A number of waste (rubber-coated cord, trim, worn hosiery) contain non-polyamide components and require a special approach when processing. Worn-out products are contaminated, and the amount and composition of contamination is determined by the operating conditions of the products, the organization of their collection, storage and transportation.

The main areas of processing and use of PA waste include grinding, melt thermoforming, depolymerization, reprecipitation from solution, various modification methods and textile processing to produce materials with a fibrous structure. The possibility, feasibility and efficiency of using certain wastes are determined, first of all, by their physical and chemical properties.

The molecular weight of waste is of great importance, which affects the strength of regenerated materials and products, as well as the technological properties of recycled PA. The content of low molecular weight compounds in PA-6 has a significant impact on strength, thermal stability and processing conditions. The most thermostable under processing conditions is PA-6.6.

To select methods and modes of processing, as well as directions for using waste, it is important to study the thermal behavior of secondary PA. In this case, the structural and chemical characteristics of the material and its background can play a significant role.

2.5.1 Methods for recycling PA waste

Existing methods for processing PA waste can be classified into two main groups: mechanical, not associated with chemical transformations, and physicochemical. Mechanical methods include grinding and various techniques and methods used in the textile industry to obtain products with a fibrous structure.

Ingots, substandard strip, casting waste, partially drawn and undrawn fibers can be subjected to mechanical processing.

Grinding is not only an operation that accompanies most technological processes, but also an independent method of waste processing. Grinding makes it possible to obtain powdered materials and crumbs for injection molding from ingots, tape, and bristles. It is characteristic that during grinding the physicochemical properties of the feedstock practically do not change. To obtain powdered products, cryogenic grinding processes are used, in particular.

Waste fibers and bristles are used to produce fishing line, washcloths, handbags, etc., but this requires significant manual labor.

Of the mechanical methods of waste processing, the production of nonwoven materials, floor coverings and staple fabrics should be considered the most promising and widely used. Of particular value for these purposes are waste polyamide fibers, which are easily processed and dyed.

Physico-chemical methods for processing PA waste can be classified as follows:

1. depolymerization of waste in order to obtain monomers suitable for the production of fibers and oligomers with their subsequent use in the production of adhesives, varnishes and other products;
2. re-melting of waste to produce granulate, agglomerate and extrusion and injection molding products;
3. reprecipitation from solutions to obtain powders for coating;
4. obtaining composite materials;
5. chemical modification for the production of materials with new properties (production of varnishes, adhesives, etc.).

Depolymerization is widely used in industry to obtain high-quality monomers from uncontaminated process waste.

Depolymerization is carried out in the presence of catalysts, which can be neutral, basic or acidic compounds.

The method of re-melting PA waste has become widespread in our country and abroad, which is carried out mainly in vertical apparatus for 2–3 hours and in extrusion plants. With prolonged thermal exposure, the specific viscosity of the PA-6 solution in sulfuric acid decreases by 0.4...0.7%, and the content of low molecular weight compounds increases from 1.5 to 5–6%. Melting in a superheated steam environment, humidification and melting in a vacuum improve the properties of the regenerated polymer, but do not solve the problem of obtaining sufficiently high-molecular-weight products.

During processing by extrusion, PA oxidizes significantly less than during long-term melting, which helps maintain high physical and mechanical properties of the material. Increasing the moisture content of the feedstock (to reduce the degree of oxidation) leads to some destruction of PA.

Obtaining powders from PA waste by reprecipitation from solutions is a method of purifying polymers and obtaining them in a form convenient for further processing. Powders can be used, for example, for cleaning dishes, as a component of cosmetics, etc.

A widely used method for regulating the mechanical properties of PA is filling them with fibrous materials (fiberglass, asbestos fiber, etc.).

An example of the highly effective use of PA waste is the creation on its basis of the ATM-2 material, which has high strength, wear resistance, and dimensional stability.

A promising direction for improving the physical, mechanical and operational properties of products made from recycled PCD is the physical modification of molded parts through their volumetric surface treatment. Volumetric-surface treatment of samples made from recycled PCA filled with kaolin and plasticized with a shale softener in heated glycerin leads to an increase in impact strength by 18% and breaking stress in bending by 42.5%, which can be explained by the formation of a more advanced structure of the material and the removal of residual stresses .

2.5.2 Technological processes for recycling PA waste

The main processes used for the regeneration of recycled polymer raw materials from PA waste are:

1. regeneration of PA by extrusion of worn-out nylon network materials and technological waste to produce granular products suitable for processing into products by injection molding;
2. regeneration of PA from worn-out products and technological waste of nylon containing fibrous impurities (not polyamides), by dissolving, filtering the solution and subsequent precipitation of PA in the form of a powdered product.

Technological processes for processing worn-out products differ from the processing of technological waste by the presence of a preliminary preparation stage, including disassembling raw materials, washing them, rinsing, squeezing and drying secondary raw materials. Pre-prepared worn-out products and process waste are sent for grinding, after which they are sent to an extruder for granulation.

Recycled fibrous polyamide raw materials containing non-polyamide materials are treated in a reactor at room temperature with an aqueous solution of hydrochloric acid and filtered to remove non-polyamide inclusions. Powdered polyamide is precipitated with an aqueous solution of methanol. The precipitated product is crushed and the resulting powder is dispersed.

Currently, in our country, technological waste generated in the production of nylon fiber is quite effectively used for the production of non-woven materials, floor coverings and granulates for casting and extrusion. The main reason for the lack of utilization of end-of-life PA products from compact sources is the lack of highly efficient equipment for their primary processing and recycling.

The development and industrial implementation of processes for processing worn-out products made from nylon fiber (hosiery, netting materials, etc.) into secondary materials will allow saving a significant amount of raw materials and directing it to the most effective areas of application.

2.6 RECYCLING POLYETHYLENE TEREPHTHALATE WASTE

Recycling of mylar fibers and worn-out PET products is similar to the recycling of polyamide waste, so in this section we will consider the recycling of PET bottles.

Over more than 10 years of mass consumption of drinks in PET packaging in Russia, according to some estimates, more than 2 million tons of used plastic containers, which are valuable chemical raw materials, have accumulated in solid household waste landfills.

The explosive growth in the production of bottle preforms, the increase in world prices for oil and, accordingly, for virgin PET, influenced the active formation in Russia in 2000 of a market for the recycling of used PET bottles.

There are several methods for recycling used bottles. One of the interesting techniques is deep chemical processing recycled PET to produce dimethyl terephthalate in the process of methanolysis or terephthalic acid and ethylene glycol in a number of hydrolytic processes. However, such processing methods have a significant drawback - the high cost of the depolymerization process. Therefore, at present, fairly well-known and widespread mechanochemical processing methods are more often used, during which the final products are formed from a polymer melt. A significant range of products made from recycled bottle polyethylene terephthalate has been developed. The main large-scale production is the production of lavsan fibers (mainly staple fibers), the production of padding polyesters and non-woven materials. A large segment of the market is occupied by the extrusion of sheets for thermoforming on extruders with sheet heads, and finally, the most promising processing method is universally recognized as obtaining granulates suitable for contact with food products, i.e. obtaining material for re-casting preforms.

The bottled intermediate product can be used for technical purposes: during processing into products, recycled PET can be added to the primary material; compounding - rPET can be fused with other plastics (for example, polycarbonate, EPE) and filled with fibers to produce technical parts; obtaining dyes (masterbatches) for the production of colored plastic products.

Also, purified PET flakes can be directly used for the manufacture of a wide range of products: textile fiber; stuffing and staple fibers - padding polyester (insulation for winter jackets, sleeping bags, etc.); roofing materials; films and sheets (painted, metallized); packaging (cartons for eggs and fruits, packaging for toys, sporting goods, etc.); injection molded products for structural purposes for the automotive industry; parts of lighting and household appliances, etc.

In any case, the starting raw material for depolymerization or processing into products is not bottle waste, which could have lain for some time in a landfill, and which are shapeless, heavily contaminated objects, but clean PET flakes.

Consider the process of recycling bottles into clean flakes of plastic.

If possible, bottles should already be collected in sorted form, without mixing with other plastics and polluting objects. The optimal object for recycling is a compressed bale of clear PET bottles (colored bottles must be sorted and recycled separately). Bottles must be stored in a dry place. Plastic bags with PET bottles in bulk are emptied into the loading hopper. Next, the bottles enter the feeder hopper. The bale feeder is used both as a storage bin with a uniform feeding system and as a bale breaker. A conveyor located on the floor of the bin moves the bale to three rotating augers, which break the agglomerates into individual bottles and feed them to the discharge conveyor. Here it is necessary to separate colored and undyed PET bottles, as well as remove foreign objects such as rubber, glass, paper, metal, and other types of plastics.

In a single-rotor crusher equipped with a hydraulic pusher, PET bottles are crushed, forming large fractions up to 40 mm in size.

The crushed material passes through an air vertical classifier. Heavy particles (PET) fall against the air flow onto the vibration separator screen. Light particles (labels, film, dust, etc.) are carried upward by the air flow and collected in a special dust collector under the cyclone. On the vibrating screen of the separator, the particles are separated into two fractions: large PET particles “flow” through the screen, and small particles (mainly heavy fractions of contaminants) pass inside the screen and are collected in a container under the separator.

A flotation tank is used to separate materials with different relative densities. The PET particles fall to the inclined bottom, and the screw continuously discharges the PET onto the water separating screen.

The screen serves both to separate the water pumped together with PET from the flotator, and to separate fine fractions of contaminants.

Pre-crushed material is effectively washed in an inclined two-stage rotating drum with perforated walls.

Drying of the flakes occurs in a rotating drum made of perforated sheet. The material turns over in hot air currents. The air is heated by electric heaters.

Next, the flakes enter the second crusher. At this stage, the large PET particles are crushed into flakes, the size of which is approximately 10 mm. It should be noted that the idea of ​​processing is that the material is not crushed into flakes of a marketable product in the first stage of grinding. This process allows you to avoid material loss in the system, achieve optimal label separation, improve the cleaning effect and reduce wear on the knives in the second crusher, since glass, sand and other abrasive materials are removed before the secondary crushing stage.

The final process is similar to that of primary air classification. Residues of labels and PET dust are removed with the air flow. The final product – pure PET flakes – is poured into barrels.

Thus, it is possible to solve the serious issue of recycling recycled plastic containers to obtain a product.

A promising way to recycle PET is to produce bottles from bottles.

The main stages of the classical recycling process for implementing the “bottle to bottle” scheme are: collection and sorting of secondary raw materials; packaging of secondary raw materials; grinding and washing; separation of crushed material; extrusion to produce granules; processing of granules in a screw apparatus in order to increase the viscosity of the product and ensure sterilization of the product for direct contact with food. But to implement this process, serious capital investments are required, since it is impossible to carry out this process on standard equipment.

2.7 BURNING

It is advisable to burn only certain types of plastics that have lost their properties to obtain thermal energy. For example, a thermal power plant in Wolverhamton (Great Britain) is the first in the world to operate not on gas or fuel oil, but on old car tires. The English Office for the Utilization of Non-Fossil Fuels helped to implement this unique project, which makes it possible to provide electricity to 25 thousand residential buildings.

The combustion of some types of polymers is accompanied by the formation of toxic gases : hydrogen chloride, nitrogen oxides, ammonia, cyanide compounds, etc., which necessitates measures to protect the atmospheric air. In addition, the economic efficiency of this process is the least compared to other plastic waste recycling processes. Nevertheless, the comparative simplicity of organizing combustion determines its fairly wide distribution in practice.

2.8 REMEDY WASTE RECYCLING

According to the latest statistics, about 2 million tons are generated annually in Western Europe worn tires, in Russia - approximately 1 million tons of tires and the same amount of old rubber are produced by rubber technical products (RTI). Enterprises producing tires and rubber goods generate a lot of waste, a considerable portion of which is not reused, for example, used butyl diaphragms from tire factories, ethylene propylene waste, etc.

Due to the large amount of old rubber, combustion still dominates in recycling, while material recycling still makes up a small share, despite the relevance of this particular recycling for improving the environment and preserving raw materials. Material recycling is not widely used due to high energy consumption and the high cost of obtaining fine rubber powders and reclaims.

Without economic regulation from the state, tire recycling still remains unprofitable. The Russian Federation does not have a system for collecting, depositing and recycling used tires and rubber goods. Methods of legal and economic regulation and incentives for solving this problem have not been developed. For the most part, used tires are accumulated in vehicle parks or taken to forests and quarries. Currently, significant amounts of used tires generated annually are a major environmental problem for all regions of the country.

As practice shows, it is very difficult to solve this problem at the regional level. In Russia, a Federal program for recycling tires and rubber goods should be developed and implemented. The Program must include legal and economic mechanisms to ensure the movement of worn tires according to the proposed scheme.

As an economic mechanism for the operation of the tire recycling system in our country, two fundamental approaches are discussed:

1. Tire disposal costs are paid directly by the owner – “the polluter pays”;
2. The tire manufacturer or importer pays for tire recycling – “manufacturer pays”.

The “polluter pays” principle is partially implemented in regions such as Tatarstan, Moscow, St. Petersburg, etc. Realistically assessing the level of environmental and economic nihilism of our fellow citizens, the successful use of the “polluter pays” principle can be considered futile.

The best thing for our country would be to introduce the “producer pays” principle. This principle works successfully in Scandinavian countries. For example, its use in Finland allows more than 90% of tires to be recycled.

2.8.1 Crushing worn tires and tubes

The initial stage of obtaining reclaim using existing industrial methods from worn rubber products (tires, tubes, etc.) is their grinding.

The grinding of tire rubber is accompanied by some destruction of the vulcanization network of the rubber, the magnitude of which, estimated by the change in the degree of equilibrium swelling, is, other things being equal, the greater, the smaller the particle size of the resulting rubber crumb. In this case, the chloroform rubber extract changes extremely slightly. At the same time, destruction of carbon structures also occurs. Crushing of rubbers containing active carbon black is accompanied by some destruction of chain structures along carbon-carbon bonds; in the case of low-active carbon black (thermal), the number of contacts between carbon particles increases slightly. In general, changes in the vulcanization network and carbon structures of rubber during crushing should, as in the case of any mechanochemical process, depend on the type of polymer, the nature and amount of filler contained in the rubber, the nature of the cross-links and density of the vulcanization network, the temperature of the process, and the degree of grinding rubber and the type of equipment used. The particle size of the resulting crumb rubber is determined by the method of rubber devulcanization, the type of rubber being crushed and the quality requirements of the final product - the reclaimed material.

How smaller sizes particles of crumbs, especially quickly and uniformly degraded material, reducing the content of insufficiently devulcanized rubber particles ("cereals") in the devulcanized product and, as a consequence of this, obtaining a more uniform quality reclaim, reducing the amount of refining waste and increasing the productivity of refining equipment. However, as the particle size of crumb rubber decreases, the cost of its production increases.

In this regard, with currently existing methods for producing crumb rubber, the use of tire rubber crumb with particle sizes of 0.5 mm or less to obtain reclaimed tires is, as a rule, not economically feasible. Since worn tires contain other materials along with rubber - textiles and metal, when crushing tires, the rubber is simultaneously cleaned of these materials. If the presence of metal in crumb rubber is unacceptable, then the possible content of textile residues in it depends on the subsequent method of devulcanization of the crumb rubber and the type of textile.

For crushing worn rubber products, rollers (in the Russian Federation, Poland, England, USA) and disk mills (in Germany, Hungary, the Czech Republic) are most widely used. Impact (hammer) crushers and rotary grinders, for example Novorotor installations, are also used for this purpose. Rubbers are also crushed using the extrusion method, which is based on the destruction of rubber under conditions of all-round compression and shear.

An apparatus is proposed in which the crushed material passes between the rotor and the housing wall. The grinding effect is enhanced by changing the size and shape of the gap between the rotor and the housing wall when the rotor rotates. A comparison of a number of existing schemes for crushing worn tires showed that in terms of equipment productivity, energy and labor intensity of the process, the scheme based on the use of rollers has better indicators than the use of disc mills or a rotary machine.

The technology for grinding worn tires existing at domestic regeneration plants makes it possible to obtain rubber crumbs from tires with textile cord.

Excerpts from the tutorial

"Recycling and recycling of polymer materials"

Klinkov A.S., Belyaev P.S., Sokolov M.V.

The use of secondary raw materials as a new resource base is one of the most dynamically developing areas of processing polymer materials in the world. For Russia it is new. However, the interest in obtaining cheap resources, which are secondary polymers, is very noticeable, so global experience in their recycling should be in demand.

In countries where environmental protection is of great importance, the volume of recycling of recycled polymers is constantly increasing. Legislation obliges legal entities and individuals to throw away polymer waste (flexible packaging, bottles, cups, etc.) in special containers for their subsequent disposal. Today, not only the task of recycling waste polymer materials, but also restoring the resource base is on the agenda. However, the possibility of using polymer waste for re-production is limited by its instability and worse mechanical properties compared to the original polymers. The final products using them often do not meet aesthetic criteria. For some types of products, the use of recycled materials is generally prohibited by current sanitary or certification standards. For example, in a number of countries there is a ban on the use of certain recycled polymers for the production of food packaging.

The process of obtaining finished products from recycled plastics is associated with a number of difficulties. Reuse of recycled materials requires special reconfiguration of process parameters due to the fact that the recycled material changes its viscosity and may also contain non-polymer inclusions. In some cases, the finished product has special mechanical requirements that simply cannot be met when using recycled polymers. Therefore, to use recycled polymers, it is necessary to achieve a balance between the desired properties of the final product and the average characteristics of the recycled material. The basis for such developments should be the idea of ​​​​creating new products from recycled plastics, as well as partially replacing primary materials with secondary ones in traditional products. Recently, the process of replacing primary polymers in production has become so intensified that in the USA alone, more than 1,400 types of products are produced from recycled plastics, which were previously produced only using primary raw materials.

In this way, recycled plastic products can be used to produce products previously made from virgin materials. For example, it is possible to produce plastic bottles from waste, i.e. closed-loop recycling. Also, secondary polymers are suitable for the manufacture of objects whose properties may be worse than those of analogues made using primary raw materials. The latest solution is called “cascade” waste processing. It is successfully used, for example, by the FIAT auto company, which recycles bumpers from used cars into pipes and mats for new cars.

We will look at the problems and prospects for reusing plastics using the example of polyethylene terephthalate (PET), polyethylene, polypropylene and polystyrene.

PAT

PET has fairly stable mechanical properties. Therefore, secondary material based on it is quite easy to recycle. The main raw materials for recycling are the ubiquitous plastic drink bottles. It is also important that rPET homogenizes more easily than other recycled plastics. In developed countries, the collection of PET waste is sufficiently established, as is the technology for its processing. The global volume of recycled PET recycling reaches 1 million tons annually.

The process of recycling PET waste does not require plasticization. They are sorted from other types of polymer containers (PVC or PE based), then crushed, washed and cleaned of labels, adhesives, packaging residues and other contaminants, and then agglomerated or granulated. Recycled PET polymers have the same processing problems as the original PET base: a low threshold for non-Newtonian behavior (when the shear rate affects the change in the viscosity of the polymer), sensitivity to heat and, finally, the need for drying. Moreover, during the drying and processing process, the recycled material undergoes some loss of viscosity, which is caused not only by temperature and deformation effects during the polymer plasticization process, but also by the presence of contaminants (moisture, glue, dyes, etc.). These factors lead to a decrease in the molecular weight of the polymer. Table 1 shows the values ​​of strength (σ) and elongation (ε) at break of film samples made from virgin PET and samples of recycled PET processed by extrusion with and without pre-drying. Insufficient drying of the recycled substrate can significantly degrade the properties of the recycled material.

Table 1

The area of ​​further use of recycled PET waste is determined by its molecular weight. The molecular weight of PET is calculated based on its intrinsic viscosity. Table 2 shows the range of its values ​​for various applications of PET.

Table 2. Intrinsic viscosity of PET depending on the application

It is obvious that secondary polymers, which form the basis of different types of products and, accordingly, have different molecular weights (inherent viscosity), require completely different recycling technologies. Recycled PET cannot always serve as a basis for re-production of original products.

Another problem with recycling PET waste is the possible presence of PVC in it. Even with careful sorting of PET bottles, there is a possibility of PVC and PE impurities getting into the recycled material. At the processing temperature, PET PVC decomposes, releasing hydrochloric acid, which causes intense destruction of the polymer. Therefore, it is necessary to minimize the presence of PVC in PET waste. The permissible PVC content does not exceed 50 ppm.

Most often, PET waste is reused to produce plastic bottles, films and fibers. The rheological and mechanical properties of recycled PET allow it to be used in the manufacture of containers for detergents, which makes it a good alternative to PVC and HDPE. Recycled PET is also often used as an interlayer in the production of three-layer amorphous film and blow molding of three-layer laminated bottles with virgin polymer outer layers. The use of coextrusion of mixtures of recycled recycled and virgin PET can improve the rheological properties of the recycled polymer, making it more suitable for blow molding.

An equally important area of ​​application for recycled PET is the production of fibers. The fiber spinning process requires the plasticizable secondary polymer to have the same rheological properties (flow rate gradient and non-isothermal draw) as the virgin polymer. As a rule, PET fiber, formed from a recycled base, has mechanical properties that satisfy the conditions for the production of a wide range of products.

Recycled fiber is processed into textiles or woven bases for clothing and carpeting. These applications can use up to 100% recycled polymer. Most often, PET fiber is used as a synthetic insulation for winter clothing or a finished corduroy texture for sewing clothes.

PET fiber has a number of advantages over other synthetic fibers. For example, carpets made from PET fibers do not fade color and do not require the special chemical treatment required for carpets made from nylon fibers. PET fibers are easier to dye than nylon. PET fiber fabrics made using melt-blown technology are used for the production of noise-insulating materials, geotextiles, filtering and absorbent elements, and padding polyester. Finally, a small amount of recycled PET is used to make automotive components, electrical products, and various accessories using injection molding.

Polyethylene

Low-density polyethylene (LDPE) and linear polyethylene (LLDPE) are used to make films for household packaging (including plastic bags, bags and sacks) and industrial packaging (for example, bags for agricultural fertilizers), which are raw materials for further recycling. In the first case, processing is quite simple, since the quality of the recycled material is very close to the quality of the primary polymer due to the short life cycle of the product. The polymer is exposed to external factors for a short period of time and undergoes only minor structural decomposition. To a greater extent, the structure of the material suffers during the process of its regeneration through plasticization. Another source of unsatisfactory properties of recycled materials can be the use of waste with different molecular structures (for example, both LDPE and LLDPE), which certainly leads to a decrease in the mechanical properties of the resulting material.

When recycling industrial packaging, the situation is somewhat more complicated. As a rule, industrial film has a longer life cycle than household film. Exposure to sunlight, temperature fluctuations, etc. also has a detrimental effect on the structure of the polymer. In addition, used industrial polyethylene films can contain significant contamination in the form of dust and fine components, which are almost impossible to remove even with the most thorough washing. Naturally, this negatively affects the properties of secondary materials.

The use of all recycled plastics is calculated based on their average properties. In the case of LDPE and LLDPE, it can be stated with varying degrees of confidence that the polymer raw materials of secondary films of these types can be processed under the same conditions (and with approximately the same final properties) as virgin plastics. Examples of recycling LDPE include the re-production of film for household and commercial packaging, bags for bulk waste, and garden mulching film. The material properties of the finished product are very close to the properties of the primary polymer base, however, the number of product-to-product recycling cycles is limited due to the deterioration of the polymer properties during the repeatedly repeated process of melting the material. In the last cycle, the recycled film is only suitable for the production of garden mulching film, which requires rather modest mechanical properties (ordinary soot is often added to it).

Stretch films have polymer additives that act as pollutants, requiring a significant addition of primary raw materials: secondary stretch film is mixed in a low proportion (15-25%) with the primary polymer. When recycling films of agro-industrial origin, a number of difficulties arise, caused not only by the deterioration of the mechanical properties of the polymer base and foreign inclusions, but also by photo-oxidative processes that reduce the optical properties of the material. The resulting film acquires a yellow tint.

Currently, the most promising direction for recycling waste from LDPE and LLDPE (and from any other polymers) is considered to be the creation of intermediate materials to replace traditional wood materials. The main advantage of recycled polymer materials over wood is its biological stability: polymers are not subject to destruction by microorganisms and can remain in water for a long time without threatening the structure. To improve the mechanical properties, various inert additives are introduced into the polymer composition, for example, pulverized wood shavings or fibers. The market for such products is huge. US Plastic Lumber Corp. estimates it at $10 billion.

For example, canisters for liquid products are made from high-density polyethylene. The process of processing HDPE waste requires special cleaning of secondary products (for example, containers for fuels and lubricants). In addition, problems often arise associated with the destruction of HDPE during the plasticization process due to the large mechanical forces accompanying the process. The scope of application of recycled HDPE is very wide and is characterized by a variety of technological processes. It is often used for the production of films, containers of various sizes, irrigation pipes, various semi-finished products, etc. Recycled HDPE has found its greatest use in the production of containers (canisters) using the blow molding method. The rheological properties of high-density recycled polymers do not allow large containers to be blown, so the volume of such canisters is limited. A typical area of ​​use for canisters based on HDPE waste is packaging of fuels and lubricants and detergents.

Canisters can be made either entirely from polymer waste or extruded with primary granulate. In the latter case, the secondary polymer layer forms a core between two layers of primary polymer. Canisters obtained in this way are used by a number of companies (Procter & Gamble, Unilever, etc.) for dispensing detergents.

Another example of mass production made from recycled HDPE is irrigation pipes. As a rule, they are made from a mixture of secondary and primary polymers in different proportions. Considering that irrigation pipes are not designed for use under pressure, the mechanical properties of recycled HDPE are ideal for their production. The high viscosity of HDPE from canister and film recycling can often be offset by the low viscosity of the virgin polymer, which can improve impact resistance. The production of large-diameter pipes from recycled HDPE is also not a problem: the diameter of irrigation and drainage pipes reaches 630 mm.

When using injection molding technology, the percentage of recycled plastic is lower. This technology is used for the manufacture of cladding panels, utility garbage containers etc. The cladding panel market is very attractive due to its large capacity. It is estimated that the US market alone consumes 2 billion units of siding panels and boards still using traditional lumber.

As for the production of film with increased impact resistance and high tensile strength, in this case recycled HDPE can only be used with LDPE and LLDPE additives.

Polypropylene

The main sources of recycled polypropylene are plastic boxes, battery housings, bumpers and other plastic parts of cars. Packaging products made from this material are less recyclable. The quality of secondary PP depends on the conditions in which the product was located during operation. The less it has suffered from external influences, the closer the properties of the secondary material are to the properties of the primary one. However, operating conditions are rarely so favorable. Only in rare cases can automotive plastic components be recycled in a closed cycle: for example, Renault uses recycled PP bumpers to make new ones in the Megane model. As a rule, recycled PP is used to produce other automotive parts that are subject to less stringent requirements - ventilation pipes, seals, mats, etc. This example fits into the classic cascade recycling scheme.

Recycled PP is also used in various mixtures with primary PP or other polyolefins for injection molding (boxes, housings) or extrusion (various profiles and semi-finished products).

Polystyrene

The possibilities for recycling polystyrene waste are much more modest. This is due to less diffusion compared to other plastics and, most importantly, less difference in price between virgin and recycled materials. In addition, polystyrene products often undergo significant volumetric stretching during the production process, which complicates recycling and affects the overall cost of disposal. Very little post-consumer polystyrene is recycled into virgin products. Examples of reusing polystyrene waste are insulating panels, packaging materials, insulating pipe lining and other products that can optimally use the good thermal insulation, noise-absorbing and impact-resistant properties of recycled polystyrene. In some cases, the structure of the recycled polystyrene is densified through the use of special transition technologies, and the material thus obtained is used in applications of crystalline polystyrene. Most interesting application of such material - the production of profiles that were previously made only from wood (window frames, floors, etc.). In this case, the properties of recycled polystyrene are in no way inferior to the properties of wood, and in terms of the duration of the life cycle under natural conditions they even surpass it.

Plastic mixtures

Disposal of products consisting of a combination of various polymers is both a labor-intensive and promising task. On the one hand, when creating secondary materials with acceptable mechanical properties from mixtures of plastics, there is no need for primary (at the municipal level) and secondary (at the recycling production level) sorting of household and industrial waste, which should have a positive impact on the cost of processing. On the other hand, the properties of the resulting materials are not very good, since the polymers that form their basis (mainly PE, PP, PET, PS and PVC) are incompatible with each other and form a multicomponent system with low interfacial interaction. Moreover, the presence of pollutants - particles of paper, metal, dyes - leads to a further deterioration of physical and mechanical properties.

In almost all cases, the properties of the mixture turn out to be much worse than the properties of each component separately. To achieve visible success in recycling multi-component waste, it is necessary to carry out processing with the shortest possible cycle. The task is, on the one hand, to avoid unnecessary material costs, and on the other, to reduce processing time, preventing the polymers that make up the material from starting to deteriorate. For this reason, it is necessary to keep the operating temperature low, even though certain components (eg PET) will remain in a solid state and behave like inert fillers. It is also necessary to choose applications that do not require high mechanical properties and do not have significant dimensions. This is the only way to avoid the serious impact of processing costs on the final cost of the product, as well as to offset the low mechanical properties of a multicomponent polymer with the small size of products formed from it.

Equipment

Various types of equipment for processing polymer waste are produced in all developed industrial countries. There are manufacturers individual species equipment for “recycling” in the CIS - for example, OJSC Kuzpolimermash (Russia), Baranovichi Machine Tool Plant (Belarus).

However, in complex solutions there are no equals to such well-known European companies as Erema GmbH, Artoc Maschinenbau GesmbH, NGR GmbH, General Plastics GmbH (Austria), Gamma Meccanica, Tria S.p.A. (Italy), Erlenbach GmbH, Sikoplast Maschinenbau, Heinrich Koch GmbH (Germany), ORVAK (Sweden). Today these companies are actively entering the Russian market.