Use of recycled polymers. Properties: behavior of secondary raw materials during processing. Equipment for polymer processing

The widespread use of polymer material implies timely disposal of raw materials and recycling for subsequent use. To carry out these actions, the following types of equipment are required: agglomeration devices, crushing mechanisms and granulating devices.

Environmental conditions dictate the need for waste-free production of polymer-type goods in order to avoid polluting the environment. For this reason, industrial production annually increases production capacity due to secondary and subsequent processing of polymers.

Agglomerators, as a result of their operation, convert the polymer into an agglomerate. This device is a mechanism for processing used polymer products. The process occurs due to the sintering of finely crushed particles into granular components. The resulting granulated raw materials are reused in production polymer products, in the form of a main or auxiliary element.

Polymer processing technology

Polymer processing involves preliminary operations in the unit sector, using appropriate knives. Further, the processing of polymers continues with heat treatment (under the influence of high temperature regime there is frequent contact of crumbs of polymer raw materials).

When operating temperatures reach one hundred degrees, the container is filled with water. The created liquid medium promotes the formation of agglomerate. The formed granular components, through a special shutter valve, are moved into a tank chamber for temporary storage and subsequent removal.

Granulators are devices that are used for... Granular processing of polymers is achieved through microcrushing operations and the formation of uniform polymer or plastic granules. The resulting granulate is used as a feedstock in the production of cast and extruded polymer substances.

As a rule, granulators are a rather complex structure, consisting of several synchronized units. The design of the equipment is presented in the form of an extruder for melting the crushed mass, a stranded head for filtering the polymer solution, and a cooling bath finished product, devices for cutting granules, a hopper for collecting granular particles.

Equipment for polymer processing

For secondary operations, polymer processing provides equipped with directed action mechanisms - crushing and grinding production lines. With their help, the preliminary preparatory process of waste polymer products for extrusion and sintering operations occurs. There are three types of different power crushing lines.

Depending on the technical equipment of the model used, shredding devices can perform sifting functions to separate small-sized elements, automatically wash and dry polymer materials. They are also equipped with moving conveyor belts, metal detectors, and noise protection, which greatly simplifies the process of processing recycled polymer mass.

Polymer recycling - necessary and environmentally friendly safe look activities that require costs for special equipment. The greatest economic effect, as a rule, is achieved by processing enterprises equipped with modern, high-performance plants. High-quality operation of the equipment is the key to an excellent result, obtaining a high-quality product in the form of raw materials for further use in the production of polymer products.

Introduction

Recycling of homogeneous polymers - relatively simple task, if their structure has been preserved and there was no significant destruction either during manufacture or during primary use (see, for example,). Of course, the destruction process, which may result in structural and morphological changes caused by a decrease in molecular weight, the formation of branches, other chemical groups, etc., leads to a significant deterioration of all physical properties. While recycled materials that retain their properties can be used in the same applications as virgin polymers, recycled materials with reduced properties can only be used in specific applications. Therefore, when mechanically recycling homogeneous polymers, the challenge is to avoid further destruction during the technological process, that is, to avoid deterioration of the properties of the final material. This can be achieved the right choice processing equipment, processing conditions (see Chapters 4 and 8) and the introduction of stabilizers (see Chapters 3 and 7).

In this chapter we will consider the relationship of the properties of homogeneous polymers with the conditions of their processing (in the order in which the properties of polymers change with increasing number of processing steps), as well as with the type of machines used; In addition, we study the dependence of properties on the initial structure.

Recycling of polyolefins and polyvinyl chloride

Introduction

Mechanical recycling of polyolefins constitutes a very important area of ​​the recycling industry. Of course, the main share here comes from raw polyolefins and, accordingly, a huge number of polyolefin products are produced, and the relative ease of their collection makes for simple and economical recycling. As with other polymers, the final properties and economic value of polyolefins depend on the degree of degradation during primary use and on the conditions of recycling. In addition, the chemical structure of polyolefins is very important in determining the properties of the recycled polymer.

Polyethylenes

The different structural types of commercial polyethylenes (PEs) greatly influence the recycling behavior of these materials. Of course, branching (short or long chains) affects the kinetics of destruction, and then the final properties of the recycled material, which has undergone several stages of processing. This behavior is of particular importance for those plastics that are subject not only to thermomechanical degradation during processing, but also to other destructive influences during subsequent use. Photo-oxidation and other types of destruction cause various structural and morphological changes, depending on the structure of the PE.

Recycling of PE is discussed in several monographs and in many articles.

The relationship between properties/processing stages will be considered both using the example of various types of commercial PE, and various types of destruction that the material experiences during its use.

High Density Polyethylene

The main sources of recovered high-density polyethylene (HDPE) are liquid containers and packaging film; In addition, the volume of recycling of automotive fuel containers is growing. In all cases molecular mass of these used HDPE products remains very high because the degradation experienced by this type of material during short-term use is very low. The latter circumstance assumes that the properties of the recycled material are close to those of the original polymer. In table Figure 5.1 compares HDPE samples obtained from recycled bottles and from virgin polymer. It is clearly seen that most of the properties are very close. As noted above, this is a result of the bottles being used for a short period of time and not undergoing significant degradation, although some structural change may have occurred during recycling; this is indicated by the expansion of the molecular weight distribution. In addition, the elastic modulus and elongation at break differ significantly, and the recycled material has slightly higher tensile strength.

These differences may result from subtle changes in structure and morphology. In particular, when processing PE melts, both chain scission (decreasing molecular weight) and branching (increasing molecular weight) can occur, making cross-linking reactions difficult to detect from molecular weight measurements, and they can change the final properties of the recycled material.

Recycled polymers go through at least two to three recycling cycles, and in each cycle, melting causes additional degradation of the material. In addition, the increase in recycled polymers and the use of recycled and virgin material blends (see Chapter 6) means that a significant proportion of recovered plastics is recycled again and again. This means that the properties of such repeatedly recycled polymer materials are constantly changing with increasing number of processing cycles in the direction of their deterioration. For example, in table. Figure 5.2 shows the changes in some properties of a HDPE sample (fuel canister) after 15 cycles of injection molding recycling.

It is clearly seen that the changes in mechanical properties are relatively small, although the melt flow rate decreases significantly. The latter circumstance can be explained by the strong dependence of viscosity on molecular weight and this means that the workability of the material has changed significantly.

The result clearly shows that the properties of recovered HDPE depend not only on the properties of the recycled products, but also on the nature and number of recycling cycles. In addition, both the properties of the melts, which determine the processability of the polymer, and the properties of the solid material are influenced to some extent by recycling

Thus, it is necessary to know the relationship between properties and recycling cycles in order to be able to predict to some extent the likely characteristics of recycled plastics and therefore determine the applications available for these materials. Of course, the final properties will depend not only on the number of processing cycles, but also on the properties of the recovered materials, the nature of the processing and its conditions.

In Fig. Figure 5.1 shows the flow curves of a HDPE sample (canister). The data refers to samples that have gone through several processing cycles on a single-screw extruder. Viscosity decreases with increasing number of recycling cycles over the entire shear rate range. This means that during repeated extrusions, thermomechanical stresses acting on the melt cause a certain destruction of the polymer. This is a simple pattern, but it is in conflict with what was observed for the same sample passing through a twin-screw extruder (Figure 5.2). In this case, the situation is much more complicated, since a small decrease in viscosity occurs only at high shear rates, and at low rates the effect is reversed. Thermomechanical stress causes both chain scission and molecular growth, mainly due to the formation of long side branches and stitching The final molecular structure depends on the relative contribution of these two processes. In particular, increasing the processing temperature and time (on a single screw extruder) favors chain breaking, resulting in a reduced viscosity of the final melt. Additionally, the nature of the competition between the two mechanisms may change with excess oxygen during processing or depending on the specific molecular structure of the HDPE sample. For example, high

the content of vinyl groups leads to a significant increase in melt viscosity - a decrease in molecular weight - and long-chain branching. Vlachopoulos et al. found that chain scission dominates in copolymers (as evidenced by chain branching), while cross-linking is the main degradation mechanism in homopolymers. The increase in extrusion pressure as the number of processing cycles increases for the last sample, and the decrease in the copolymer sample, occurs due to the increase and decrease in molecular weight, which is confirmed by these mechanisms. This means that it is very difficult to predict changes in the structure of recovered HDPE and therefore its rheological and mechanical properties, since this material consists of copolymer and homopolymer polymers. In addition, homopolymers may contain varying numbers of vinyl groups. The extrusion quality of the bottle recovery material tested in the same work was indeed independent of the extruder passes, indicating that both mechanisms play the same role and that the recovered material is, as already assumed, a mixture HDPE copolymer and homopolymer.

The data presented shows that the type of recycling machines and processing conditions significantly, and sometimes decisively, influence the final properties of the recycled material - in this case the HDPE sample. As an example in Fig. Figures 5.3 and 5.4 show modulus and elongation at break as a function of the number of passes through the extruder. The mechanical properties of the two samples changed completely differently.

The elastic modulus curve increases with the number of processing steps, while the elongation at break behavior shows the opposite trend. Moreover, the modulus curve of the sample processed in a single-screw extruder is higher than that of the sample extruded in a twin-screw extruder, but its elongation at break is lower. The unexpected behavior of the dependence of the modulus on the number of processing cycles was explained by an increase in crystallinity with a decrease in molecular weight. The same reason that causes a decrease in molecular weight causes a decrease in elongation at break. A more pronounced increase in modulus and a decrease in elongation at break of the sample processed on a single-screw extruder reflects the fact of more significant destruction of the melt in this machine. This is mainly due to longer processing times.

The influence of the structure on the mechanical properties of recycled HDPE becomes clearer if you look at the values ​​of crack resistance under external stress given in Table. 5.3. Data refer to homopolymer, copolymer and post-consumer samples after 0 and 4 passes through a single screw extruder.

Two initial samples demonstrate deterioration in crack resistance under external stress, but the drop in properties of the copolymer after repeated recycling is catastrophic. The crack resistance value of the recovered material after four passes through the extruder decreases by

20%, although it consists mainly of copolymer. The significant change in the crack resistance of the copolymer appears to be balanced by an improvement in the behavior of the homopolymer fraction.

The data presented clearly shows the influence of the structure of HDPE and the nature of the processing equipment on the final properties of the recycled polymer.

The main uses of recycled HDPE are in the manufacture of liquid containers (including multi-layer bottles with recycled HDPE linings), drainage pipes, granules and films for bags and trash bags.

As part of the CREON Group

Polymer recycling, so developed in European countries, is still in its infancy in Russia: separate waste collection is not established, there is no regulatory framework, there is no infrastructure, and there is no awareness among the majority of the population. However, market players look to the future with optimism, placing hopes, among other things, on the Year of Ecology, which was declared in the country in 2017 by presidential decree.

Third international Conference“Polymer Recycling 2017”, organized by INVENTRA, took place in Moscow on February 17. The event partners were Polymetrix, Uhde Inventa-Fischer, Starlinger Viscotec, MAAG Automatik, Erema and Moretto; support was provided by Nordson, DAK Americas and PETplanet. The information sponsor of the conference is the magazine “Polymer Materials”.

“The current situation is not inspiring, but its improvement is a matter of time,” said Sergei Stolyarov, Managing Director of the CREON Group, in his welcoming speech. – With high prices for primary raw materials, the demand for processed polymers and products made from them will grow. At the same time, the emergence of domestic raw materials will shift the consumption structure of virgin PET towards fibers and films. In this regard, the use secondary polymers becomes especially promising.”

At the end of 2016, the global collection of PET for recycling amounted to 11.2 million tons, said PCI Wood Mackenzie consultant Helen McGee. The main share came from Asian countries - 55%, Western Europe collected 17% of the world volume, and the USA - 13%. According to the expert's forecast, by 2020, PET collections for recycling will exceed 14 million tons, and in percentage terms, the collection level will reach 56% (currently 53%). The main growth is expected to come from Asian countries, in particular China.

At the moment, the highest level of collection is observed in China, it is 80%; other Asian countries have reached approximately the same figure. According to Ms. McGee, from the PET collected in 2016 (which, recall, is 11.2 million tons), production losses amounted to 2.1 million tons, respectively, 9.1 million tons of flakes were obtained. The main direction of further processing is fibers and threads (66 %).

By 2025, 60% of household waste in Europe will be recycled; in 2030, this figure will rise to 65%. Such amendments are planned to the Waste Framework Directive, said Kaspars Fogelmanis, Chairman of the Board of Directors of Nordic Plast. Now the level of recycling is much lower - in Latvia, for example, it is only 21%, on average in Europe - 44%. At the same time, the volumes of plastic packaging produced in the Baltics are growing annually; the most common recycled polymers are LDPE film, HDPE and PP.

In Russia, at the end of 2016, consumption of recycled PET (rePET) amounted to about 177 thousand tons, of which 90% was domestic collection. According to Konstantin Rzaev, Chairman of the Board of Directors of EcoTechnologies Group of Companies, almost 100% of imports were PET flakes for the production of polyester fiber. The largest supplying countries are Ukraine (more than 60%), as well as Kazakhstan, Belarus, Azerbaijan, Lithuania and Tajikistan.

Konstantin Rzaev noted that last year the collection level exceeded 25% for the first time, and this suggests the emergence of a full-fledged industry in Russia that is already of interest for investment. Today, the main consumer (62% of the total volume) and price driver is still the recycled PET fiber segment. But changes in legislation and a trend towards the priority use of recycled materials within strategies Sustainable Development transnational consumer goods manufacturing companies provide fertile ground for the development of another key segment of rePET consumption - bottle-to-bottle.

Over the past year, no new large production facilities have emerged that consume rePET, but its use in the sheet segment is gradually increasing. However, already in 2017, the opening of new production of recycled PET fiber and the expansion of existing ones is expected, which, together with the ruble exchange rate, will be the main factor influencing the market balance and prices for rePET.

However, there are many other areas - not yet developed, but quite promising, where recycled PET is also in demand. As the honorary president of ARPET Viktor Kernitsky said, these are threads for furniture fabrics, car upholstery and various types of geosynthetics, foam materials for heat and sound insulation, sorption materials for cleaning Wastewater, as well as fibers reinforcing bitumen for road construction. According to the expert, there are many new processing technologies and applications, and the goal of public policy should not be to limit the use of PET, but to collect and rationally use its waste.

The topic was continued by Lyubov Melanevskaya, executive director of the RusPEC association, who spoke about the first results of the introduction of extended producer responsibility (EPR) in Russia. It came into force in 2016, its goal is to create a constant, solvent and growing demand for the recycling of product and packaging waste. After a year, it is already possible to draw some conclusions, the main one of which is that there are a number of problems due to which the mechanism for implementing the EPR often simply does not work. As Ms. Melanevskaya said at the conference, there is a need to change and supplement the existing regulation. In particular, when declaring goods, including packaging, manufacturers were faced with a discrepancy between the product packaging codes and the codes specified in the adopted regulations, as a result of which many manufacturers and importers were unable to submit declarations, because did not find themselves in regulation. The solution was to abandon codes and propose to switch to packaging identification based on materials.

In the future, RusPEC believes, it is necessary to adopt a single end-to-end terminology for all elements of the EPR and define unambiguous, understandable and transparent conditions for concluding contracts with waste management operators. In general, the association supports the EPR law as necessary and positive for the industry.

When introducing and popularizing PET recycling in the country, the availability of modern technologies(as a rule, they are provided by foreign companies). Thus, Polymetrix offers modern comprehensive solutions for PET recycling, including its own SSP technology, for recycling PET bottles into food-grade polyethylene terephthalate bottles. Now there are 21 such lines operating in the world, said Danil Polyakov, regional sales manager. The technology is aimed at the premium market and involves processing bottles into pellets for food containers. The first step is washing, where paper fibers and surface contaminants, as well as labels and glue are completely removed. Next, the bottles are crushed into flakes, which are sorted by morphology and color. Then the production of granules occurs and then the final complete purification and restoration of the characteristics of the polymer at the SSP stage.

Viscotec offers its customers technology for converting PET bottles into sheets, says company spokesman Gerhard Osberger. Thus, solid-phase polycondensation reactors viscoSTAR and deCON are designed to purify and increase the viscosity of PET granules and flakes. They are used after the granulator, before production extrusion equipment, or as a stand-alone unit. The ViscoSHEET line is capable of producing a tape made from 100% rPET and fully suitable for use with food products.

Erema company representative Christophe Vioss spoke about the continuous production of food plastic bottles from PET flakes. The VACUREMA® inline system makes it possible to process flakes directly into finished thermoforming sheet, bottle preform, finished packaging tape or monofilament.

Summing up the results of the conference, its participants identified the main factors hindering the development of polymer recycling in Russia. They named the main one as the lack of regulatory documents:

“However, there is another factor that we cannot ignore - this is public consciousness,” says conference director Rafael Grigoryan. – Unfortunately, our mentality today is such that separate waste collection is perceived more as pampering than as the norm. And no matter what progress we observe in other areas, it is necessary, first of all, to change the thinking of our fellow citizens. Without this, even the most modern infrastructure will be useless.”

1. INTRODUCTION

One of the most tangible results anthropogenic activities 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. Production of plastics at modern stage development is increasing by an average of 5...6% annually and is projected to reach 250 million tons by 2010. Their per capita consumption in industrialized countries has doubled over the past 20 years, reaching 85...90 kg. By the end of the decade, both 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. Of the total level of waste, only 5...7% of its 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 properties 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.

Disposal problems polymer waste, enough. 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 last years Research into self-destructive polymers has declined significantly, mainly because production costs for such polymers are typically significantly 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. The positive side of recycling is also that it produces an additional amount of useful products for various sectors of the national economy and does not re-contaminate 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. Degradation occurs at high temperatures 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 for processing PET waste is its breakdown 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.

The change in chemical structure begins already in the process primary processing PO, in particular during extrusion, when the polymer is subjected to significant thermal-oxidative and mechanochemical influences. Greatest contribution Photochemical processes introduce changes that occur during operation. 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 effect is particularly effective in the early stages of aging, while the 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 boundary 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 great importance have its rheological characteristics. 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), grinding, 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.

A characteristic feature of all knife crushers 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

Various types of dryers are used for drying waste: 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. More effective way– modification of secondary polymers, as well as the creation of highly filled secondary polymer materials.

2.2.3 Methods for modifying secondary polyolefins

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, as well as have reproducible physicomechanical 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 in it, which help stabilize HPEN 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, therefore it is proposed to extrude primary and secondary PVC on different cars, however, powdered PVC can almost always be mixed with recycled 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. At enterprises light industry Russia has the following technology for recycling 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 for using PVC waste is multi-component casting. With this processing method, the product has outer and inner layers of various 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 dispersion conditions under which the most highly dispersed product is formed are the temperature in the dispersant zones 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 elastic-deformation 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, mainly spherical in shape, is formed.

Elastic-deformation effect when dispersing rigid PVC materials (impact-resistant material for bottles under mineral water, plumbing PVC pipes, etc.) must be carried out at higher temperatures (170...180...70 °C), a load rate of no more than 40% and a minimum screw rotation speed of 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-disc 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 Low quality mainly destroyed by burning. 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 into 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 it much more difficult to agglomerate PS 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 before processing industry There is a problem of recycling 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 wastes (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. Significant influence The strength, thermal stability and processing conditions are influenced by the content of low molecular weight compounds in PA-6. 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 of 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 The processing of worn-out products differs 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 the deep chemical processing of recycled PET to produce dimethyl terephthalate through 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 producing 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 of used tires are generated annually in Western Europe, in Russia - approximately 1 million tons of tires and the same amount of old rubber is 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 the 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.

The smaller the particle size of the crumbs, the more quickly and evenly the degraded material is reduced, the content of insufficiently devulcanized rubber particles (“grits”) in the devulcanized product is reduced and, as a consequence of this, the regenerate is obtained more uniform in quality, the amount of refining waste is reduced and the productivity of refining equipment is increased. . 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 teaching aid

"Recycling and recycling of polymer materials"

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

11.08.2015 16:09

Waste classification

Waste is generated during the processing of polymers and the manufacture of products from them - this is technological waste, partially returned to the process. What remains after using plastic products - various films (greenhouse, construction, etc.), containers, household and large-scale packaging - is household and industrial waste.

Technological waste is subjected to thermal effects in the melt, and then during crushing and agglomeration - also to intense mechanical effects. In the polymer mass, processes of thermal and mechanical destruction occur intensively with the loss of a number of physical and mechanical properties and, with repeated processing, can negatively affect the properties of the product. So, when returning to the main process, as usual, 10-30 percent secondary waste, a noticeable amount of material goes through up to 5 cycles of extrusion and crushing.

Household and industrial waste is not only processed several times at high temperatures, but is also exposed to prolonged exposure to direct sunlight, oxygen and air moisture. Greenhouse films can also come into contact with toxic chemicals, pesticides, and iron ions, which contribute to the destruction of the polymer. As a result, a large number of active compounds accumulate in the polymer mass, accelerating the decomposition of polymer chains. The approach to recycling such different wastes should accordingly be different, taking into account the background of the polymer. But first, let's look at ways to reduce the volume of waste generated.

Reducing the amount of process waste

The amount of process waste, primarily start-up waste, can be reduced by using thermal stabilizers before stopping the extruder or injection molding unit, in the form of a so-called stop concentrate, which many people forget or neglect. When equipment is stopped, simple material in the extruder or injection molding cylinder is under the influence of high temperature when cooling and then heating the cylinder. During this time, the processes of crosslinking, decomposition and burning of the polymer actively occur in the cylinder, products accumulate, which, after start-up, come out for a long time in the form of gels and colored inclusions (burnts). Thermal stabilizers prevent these processes, thereby facilitating and speeding up cleaning of equipment after startup. To do this, before stopping, 1-2 percent of stop concentrate is injected into the machine cylinder for 15-45 minutes. before stopping at the rate of displacement of 5-7 cylinder volumes.

Processing (extrusion) additives, which increase the manufacturability of the process, can also reduce the amount of waste. By their nature, these additives, for example, Dynamar from Dyneon, Viton from DuPont, are derivatives of fluororubbers. They are poorly compatible with basic polymers and in places of greatest shear forces (dies, sprues, etc.) they are deposited from the melt onto the metal surface, creating on it a wall lubricating layer along which the melt slides during molding. The use of a processing additive in the smallest quantities (400-600 ppm) makes it possible to solve numerous technological problems - reduce torque and pressure on the extruder head, increase productivity while reducing energy costs, eliminate defects in appearance and reduce the extrusion temperature of polymers and compositions that are sensitive to high temperatures. temperatures, increase the smoothness of products, produce thinner films. When producing large-sized or thin-walled injection molded products with complex shapes, the use of an additive can improve flowability, remove surface defects, weld lines and improve the appearance of the product. All this in itself reduces the marriage rate, i.e. amount of waste. In addition, the processing additive reduces the adhesion of carbon deposits on the die, fouling of the gates, and has a washing effect, i.e. reduces the number of stops to clean equipment, which means the amount of startup waste.

The use of cleaning concentrates has an additional effect. They are used when cleaning casting and film equipment for rapid transition from color to color without stopping, most often in a 1:1-1:3 ratio with the polymer. This reduces the amount of waste and time spent changing colors. The composition of cleaning concentrates produced by many domestic (including Klinol, Cleanstair from NPF Bars-2, Lastik from Stalker LLC) and foreign manufacturers (for example, Shulman - Polyklin "), usually include soft mineral fillers and surfactant detergent additives.

Reducing the amount of household and industrial waste.

There are various ways to reduce the amount of waste by increasing the service life of products, primarily films, through the use of thermal and light-stabilizing additives. By extending the service life of the greenhouse film from 1 to 3 seasons, the amount of waste to be disposed of is correspondingly reduced. To do this, it is enough to introduce small amounts of light stabilizers into the film, no more than half a percent. The costs of stabilization are low, but the effect when recycling films is significant.

The reverse way is to accelerate the decomposition of polymers by creating photo- and biodegradable materials that quickly degrade after use under the influence of sunlight and microorganisms. To obtain photodegradable films, comonomers with functional groups that promote photodestruction (vinyl ketones, carbon monoxide) are introduced into the polymer chain, or photocatalysts are introduced into the polymer as active fillers that promote the rupture of the polymer chain under the influence of sunlight. Dithiocarbamates, peroxides or oxides of transition metals (iron, nickel, cobalt, copper) are used as catalysts. The Institute of Water Chemistry of the National Academy of Sciences of Ukraine (V.N. Mishchenko) has developed experimental methods for the formation of nanosized cluster structures containing metal and oxide particles on the surface of titanium dioxide particles. The rate of film decomposition increases 10 times - from 100 to 8-10 hours.

The main directions for obtaining biodegradable polymers:

synthesis of polyesters based on hydroxycarbonic (lactic, butyric) or dicarboxylic acids, but so far they are much more expensive than traditional plastics;

plastics based on reproducible natural polymers (starch, cellulose, chitosan, protein), the raw material base of such polymers is, one might say, unlimited, but the technology and properties of the resulting polymers have not yet reached the level of basic large-scale polymers;

imparting biodegradability to industrial polymers (polyolefins primarily, as well as PET) by compounding.

The first two areas require large capital expenditures for the creation of new production facilities; the processing of such polymers will also require significant changes in technology. The simplest way is compounding. Biodegradable polymers are obtained by introducing biologically active fillers (starch, cellulose, wood flour) into the matrix. So, back in the 80s, V.I. Skripachev and V.I. Kuznetsov from ONPO Plastpolymer developed starch-filled films with accelerated aging. Unfortunately, the relevance of such material was purely theoretical at that time, and even now it is not widely used.

Recycling

You can give the polymer a second life with the help of special complex concentrates - recyclizers. Since the polymer undergoes thermal destruction at each stage of processing, photo-oxidative destruction during the operation of the product, mechanical destruction during grinding and agglomeration of waste, destruction products accumulate in the mass of the material, and contains a large number of active radicals, peroxide and carbonyl compounds that promote further decomposition and cross-linking of polymer chains. Therefore, the composition of such concentrates includes primary and secondary antioxidants, heat and light stabilizers of the phenolic and amine type, as well as phosphites or phosphonites that neutralize active radicals accumulated in the polymer and decompose peroxide compounds, as well as plasticizing and combining additives that improve the physical and mechanical properties properties of the secondary material and bring them more or less close to the level of the primary polymer.

Complex additives from Siba. The Siba company, Switzerland, offers a family of complex stabilizers for the processing of various polymers - high-density polyethylene, HDPE, PP: Recyclostab and Recyclossorb. They are tableted mixtures of various photo- and thermal stabilizers with a wide range of melting temperatures (50-180°C), suitable for introduction into processing equipment. The nature of the additives in Recyclostab is common for polymer processing - phenolic stabilizers, phosphites and processing stabilizers. The difference lies in the ratio of components and in the selection of the optimal composition in accordance with the specific task. “Recyclossorb” is used when light stabilization plays an important role, i.e. The resulting products are used outdoors. In this case, the proportion of light stabilizers is increased. The company's recommended input levels are 0.2-0.4 percent.

"Recyclostab 421" is specially designed for processing and thermal stabilization of waste LDPE films and mixtures with a high content of LDPE.

"Recyclostab 451" is designed for processing and thermal stabilization of waste PP and mixtures with high content.

Recyclostab 811 and Recyclossorb 550 are used to extend the life of recycled products exposed to sunlight, so they contain more light stabilizers.

Stabilizers are used in the production of injection molded or film products from recycled polymers: boxes, pallets, containers, pipes, films for non-critical purposes. They are produced in granular, non-dusting form, without a polymer base, pressed granules with a melting limit of 50-180°C.

Complex concentrates from the company "Bars-2". To process secondary polymers, NPF Bars-2 produces complex polymer-based concentrates containing, in addition to stabilizers, also combining and plasticizing additives. Complex concentrates "Revtol" - for polyolefins or "Revten" - for impact-resistant polystyrene, are introduced in an amount of 2-3 percent when processing recycled plastics and, thanks to a set of special additives, prevent thermal-oxidative aging of secondary polymers. Concentrates facilitate their processing due to improved rheological characteristics of the melt (increased MFR), increase the strength characteristics of finished products (their ductility and resistance to cracking) compared to products made without their use, facilitate their processing as a result of increasing the manufacturability of the material (reduced torque and drive load). When processing mixtures of secondary polymers, “Revtol” or “Revten” improves their compatibility, so the physical and mechanical properties of the resulting products also increase. The use of Revten makes it possible to increase the properties of secondary UPM to the level of 80-90 percent of the properties of the original polystyrene, preventing the appearance of defects.

Nowadays, the development of a complex concentrate for processing recycled PET is very relevant. The main problem here is yellowing of the material, accumulation of acetaldehyde, and a decrease in melt viscosity. There are known additives from Western companies - Siby, Clarianta, which help overcome yellowing and improve the processability of the polymer. However, in the West and here we have a different approach to the use of recycled PET. If there 90 percent of it is used to produce polyester fibers or technical products and additives for this purpose are well developed, then our processors strive to return recycled PET to the main process - the production of preforms and bottles by casting and blow molding or the production of films and sheets by flat-slot extrusion. In this case, the target properties of the polymer that need to be influenced are somewhat different - manufacturability, moldability, transparency, and the formulation of complex additives must meet the goal.