Recycling of polymer products. Rubric “Secondary polymers” Equipment for polymer recycling

During the operation of products made of polymers, wastes appear.

Used polymers under the influence of temperature, environment, air oxygen, various radiations, moisture, depending on the duration of these influences, change their properties. Significant volumes of polymer materials that have been used for a long time and are thrown into landfills pollute the environment, so the problem of recycling polymer waste is extremely relevant. At the same time, these wastes are good raw materials with appropriate adjustment of the compositions for the manufacture of products for various purposes.

Used polymeric building materials include polymeric films used for covering greenhouses, for packaging building materials and products; barn flooring: rolled and tiled polymeric materials for floors, finishing materials for walls and ceilings; heat and sound insulating polymeric materials; containers, pipes, cables, molded and profile products, etc.

In the process of collection and disposal of secondary polymeric raw materials, various methods for identifying polymers are used. Among the many methods, the following are the most common:

· IR-spectroscopy (comparison of the spectra of known polymers with recyclable ones);

Ultrasound (US). It is based on the attenuation of US. Index is determined HL the ratio of the attenuation of the sound wave to the frequency. The ultrasonic device is connected to a computer and installed on the technological line of waste disposal. For example, index HL LDPE 2.003 10 6 sec with a deviation of 1.0%, and HL PA-66 - 0.465 10 6 sec with a deviation of ± 1.5%;

· X-rays;

laser pyrolysis spectroscopy.

The separation of mixed (domestic) waste thermoplastics by type is carried out by the following main methods: flotation, separation in liquid media, aero separation, electro separation, chemical methods and deep cooling methods. The most widely used method is the flotation method, which allows the separation of mixtures of industrial thermoplastics such as PE, PP, PS and PVC. Separation of plastics is carried out 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; purity of products - not less than 96%. Flotation and separation methods in heavy media are the most efficient and cost-effective of all those listed above.

Recycling of used polyolefins

Waste of agricultural PE film, fertilizer bags, pipes for various purposes, out of service, waste from other sources, as well as mixed waste are to be disposed of with their subsequent use. For this, special extrusion plants are used for their processing. When polymer waste is received for processing, the melt flow rate must be at least 0.1 g/10 min.

Before starting processing, a rough separation of waste is carried out, taking into account their distinctive features. After that, the material is subjected to mechanical grinding, which can be both at normal (room) temperature or in a cryogenic method (in an environment of refrigerants, for example, liquid nitrogen). Shredded waste is fed into the washing machine for washing, which is carried out in several stages with special washing mixtures. The mass wrung out in a centrifuge with a moisture content of 10–15% is fed for final dehydration to a dryer, to a residual moisture content of 0.2%, and then to an extruder. The polymer melt is fed by the extruder screw through the filter into the strand head. The cassette or rewind filter is used to clean the polymer melt from various impurities. The purified melt is pressed through the strand holes of the head, at the exit of which the strands are cut with knives into granules of a certain size, which then fall into the cooling chamber. Passing through a special installation, the granules are dehydrated, dried and packed into bags. If it is necessary to process thin PO films, then an agglomerator is used instead of an extruder.

Drying of waste is carried out by various methods, using shelf, belt, bucket, fluidized bed, vortex and other dryers, the productivity of which reaches 500 kg/h. Due to the low density, the film floats, and the dirt settles on the bottom.

Dehydration and drying of the film is carried out on a vibrating screen and in a vortex separator, its residual moisture content is not more than 0.1%. For ease of transportation and subsequent processing into products, the film is granulated. 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 on standard equipment.

For plasticization of crushed and purified polyolefin waste, single-screw extruders with a screw length (25–33) are used. D, equipped with a continuous filter for melt purification and having a degassing zone, allowing to obtain granules without pores and inclusions. When processing contaminated and mixed waste, disk extruders of a special design are used, with short multi-thread worms (3.5–5) long D having a cylindrical nozzle in the extrusion zone. The material melts in a short period of time, and fast homogenization of the melt is ensured. By changing the gap between the cone nozzle and the shell, you can adjust the shear force and friction force, while changing the mode of melting and homogenization of processing. The extruder is equipped with a degassing unit.

Granules are produced mainly in two ways: head granulation and underwater granulation. The choice of granulation method depends on the properties of the thermoplastic being processed and, in particular, 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 strands, which are cut off by knives sliding along the spinneret plate. The resulting granules with a size of 4–5 mm (in length and diameter) are discarded with a knife from the head into the cooling chamber, and then fed into the moisture extraction device.

When using equipment with a large unit capacity, 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 die. After passing through a cooling bath with water, the strands enter the cutting device, where they are cut into pellets by rotating cutters.

The temperature of the cooling water entering the bath along the countercurrent of the strands is maintained within 40–60 °C, and the amount of water is 20–40 m 3 per 1 ton of granulate.

Depending on the size of the extruder (the size of the screw diameter and its length), the productivity varies depending on the rheological characteristics of the polymer. The number of outlet holes in the head can be in the range of 20–300.

From the granulate, packages for household chemicals, hangers, construction parts, pallets for transporting goods, exhaust pipes, lining of drainage channels, non-pressure pipes for melioration and other products are obtained, which are characterized by reduced durability compared to products obtained from virgin polymer. Studies of the mechanism of degradation processes occurring during the operation and processing of polyolefins, their quantitative description allow us to conclude that the products obtained from recycled materials must have reproducible physical, mechanical and technological indicators.

More acceptable is the addition of secondary raw materials to the primary in an amount of 20–30%, as well as the introduction of plasticizers, stabilizers, fillers up to 40–50% into the polymer composition. Chemical modification of recycled polymers, as well as the creation of highly filled recycled polymer materials, allows even wider use of used polyolefins.

Modification of recycled polyolefins

Modification methods of secondary polyolefin raw materials can be divided into chemical (crosslinking, introduction of various additives, mainly of organic origin, treatment with organosilicon liquids, etc.) and physical and 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 HLDPE are achieved by introducing 2–2.5% dicumyl peroxide on rollers at 130°C for 10 min. 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 crosslinking decreases with an increase in temperature and an increase in the duration of rolling as a result of a competing degradation process. This allows you to adjust the degree of crosslinking, physical, mechanical and technological characteristics of the modified material. A method has been developed for molding products from HLDPE by introducing dicumyl peroxide directly in the process of processing, and prototypes of pipes and molded products containing 70–80% of the gel fraction have been obtained.

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

Modification of HLDPE with maleic anhydride in a disk extruder also leads to an increase in its strength, heat resistance, adhesiveness and resistance to photoaging. In this case, the modifying effect is achieved at a lower concentration of the modifier and a shorter duration of the process than with the introduction of elastomer. A promising way to improve the quality of polymer materials from recycled polyolefins is thermomechanical treatment with organosilicon compounds. This method allows 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 unsaturated bonds and oxygen-containing groups of secondary polyolefins.

The technological process for obtaining a 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; regranulation of modified waste.

In addition to the solid-phase modification method, a method for modifying VPE in solution is proposed, which makes it possible to obtain an VLDPE powder with a particle size of not more than 20 μm. This powder can be used for processing into products by rotational molding and for coating by electrostatic spraying.

Filled polymer materials based on recycled polyethylene raw materials

Of great scientific and practical interest is the creation of filled polymeric materials based on recycled polyethylene raw materials. The use of polymeric materials from recycled materials containing up to 30% filler will make it possible to release up to 40% of primary raw materials and send it to the production of products that cannot be obtained from secondary raw materials (pressure pipes, packaging films, reusable transport containers, etc.).

To obtain filled polymeric materials from recycled materials, it is possible to 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 rubber crumb). Almost all thermoplastic waste can be filled, as well as mixed waste, which for this purpose is also preferable from an economic point of view.

For example, the expediency of using lignin is associated with the presence of phenolic compounds in it, which contribute to the stabilization of WPE 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, limestone, oil shale ash, coal spheres and iron are used as cheap inert fillers.

With the introduction of finely dispersed phosphogypsum granulated in polyethylene wax into WPE, compositions with increased elongation at break were obtained. This effect can be explained by the plasticizing effect of polyethylene wax. Thus, the tensile strength of VPE filled with phosphogypsum is 25% higher than that of VPE, and the tensile modulus is 250% higher. The reinforcing effect when mica is introduced into the HPE is associated with the features of the crystalline structure of the filler, a high characteristic ratio (the ratio of the flake diameter to the thickness), and the use of crushed, powdery WPE allows you to preserve the structure of the flakes with minimal destruction.

Among polyolefins, along with polyethylene, significant volumes fall on the production of products from polypropylene (PP). The increased strength properties of PP in comparison with polyethylene and its resistance to the environment indicate the relevance of its recycling. The secondary PP contains a number of impurities, such as Ca, Fe, Ti, Zn, which contribute to the crystal formation nuclei and the creation of a crystalline structure, which leads to an increase in the rigidity of the polymer and high values ​​of both the initial elastic modulus and the quasi-equilibrium modulus. To assess the mechanical performance of polymers, the method of relaxation stresses at various temperatures is used. Secondary PP under the same conditions (in the temperature range of 293–393 K) withstands much higher mechanical stresses without destruction than the primary one, which makes it possible to use it for the manufacture of rigid structures.

Recycling of used polystyrene

Used polystyrene plastics can be used in the following areas: recycling of technological waste of high impact polystyrene (HIPS) and acrylonitrile butadiene styrene (ABS) - plastic by injection molding, extrusion and pressing; disposal of used products, EPS waste, mixed waste, disposal of heavily polluted industrial waste.

Significant volumes of polystyrene (PS) fall on foamed materials and products made from them, the density of which is in the range of 15–50 kg/m 3 . These materials are used to make mold matrices for packaging, cable insulation, boxes for packing vegetables, fruits and fish, insulation for refrigerators, refrigerators, pallets for fast food restaurants, formwork, heat and sound insulation boards for insulating buildings and structures, etc. In addition, when transporting used such products, transportation costs are sharply reduced due to the low bulk density of foamed PS waste.

One of the main methods of recycling foamed polystyrene waste is a mechanical recycling method. For agglomeration, specially designed machines are used, and for extrusion, twin-screw extruders with degassing zones are used.

The consumer point is the main location for the mechanical recycling of used EPS products waste. Contaminated foamed PS waste is subject to inspection and sorted. At the same time, impurities are removed in the form of paper, metal, other polymers and various inclusions. The polymer is crushed, washed and dried. The polymer is dehydrated by centrifugation. The final grinding is carried out in a drum, and from it the waste enters a special extruder, in which the polymer prepared for processing is compressed and melted at a temperature of about 205–210 °C. For additional purification of the polymer melt, a filter is installed, which operates on the principle of rewinding the filter material or a cassette type. The filtered polymer melt enters the degassing zone, where the screw has a deeper thread compared to the compression zone. Next, the polymer melt enters the strand head, the strands are cooled, dried and granulated. In the process of mechanical regeneration of PS waste, processes of destruction and structuring occur, so it is important that the material is subjected to minimal shear stress (a function of screw geometry, speed and melt viscosity) and a short residence time under thermomechanical load. The reduction of destructive processes is carried out due to the halogenation of the material, as well as the introduction of various additives into the polymer.

The mechanical recycling of expanded polystyrene is regulated based on the area of ​​application of the recycled polymer, for example, for the production of insulation, cardboard, cladding, etc.

There is a method for depolymerization of polystyrene waste. To do this, PS or foamed PS waste is crushed, loaded into a sealed vessel, heated to the decomposition temperature, and the released secondary styrene is cooled in a refrigerator and the monomer thus obtained is collected in a sealed vessel. The method requires complete sealing of the process and significant energy consumption.

Recycling of used polyvinyl chloride (PVC)

Recycling of recycled PVC involves the processing of used films, fittings, pipes, profiles (including window frames), containers, bottles, plates, roll materials, cable insulation, etc.

Depending on the composition of the composition, which may consist of vinyl plastic or plastic compound and the purpose of secondary PVC, recycling methods may be different.

For recycling, PVC product waste is washed, dried, crushed and separated from various inclusions, incl. metals. If products are made from compositions based on plasticized PVC, cryogenic grinding is most often used. If the products are made of rigid PVC, then mechanical crushing is used.

The pneumatic method is used to separate the polymer from the metal (wires, cables). The separated plasticized PVC can be processed by extrusion or injection molding. The magnetic separation method can be used to remove metallic and mineral inclusions. To separate the aluminum foil from the thermoplastic, heating in water at 95–100 °C is used.

Separation of labels from unusable containers is carried out by immersion in liquid nitrogen or oxygen at a temperature of about -50 ° C, which makes the labels or adhesive brittle and then allows them to be easily shredded and separated from a homogeneous material, such as paper. For the processing of artificial leather (IR) waste, PVC-based linoleums, a method for the dry preparation of plastic waste using a compactor is proposed. It includes a number of technological operations: grinding, separation of textile fibers, plasticization, homogenization, compaction and granulation, where additives can also be introduced.

Cable waste with PVC insulation enters the crusher and is fed by a conveyor to the loading hopper of the cryogenic mine, which is a sealed container with a special transport screw. Liquid nitrogen is supplied to the mine. The cooled crushed waste is unloaded to the grinding machine, and from there it enters the metal separation device, where the brittle polymer is deposited and passed through the electrostatic corona of the separator drum and copper is extracted there.

Significant volumes of used PVC bottles require different methods of their disposal. Noteworthy is the method of separating PVC from various impurities according to the density of the calcium nitrate solution in the bath.

The mechanical process of recycling PVC bottles provides for the main stages of the process of processing waste of secondary thermoplastics, but in some cases it has its own distinctive features.

During the operation of various buildings and structures, significant volumes of metal-plastic window frames based on PVC compositions that were in use are formed. Recycled PVC frames with frames, which were in use, contain approximately 30% wt. PVC and 70% wt. glass, metal, wood and rubber. On average, a window frame contains about 18 kg of PVC. The incoming frames are unloaded into a container 2.5 m wide and 6.0 m long. Then they are pressed on a horizontal press and turned into sections up to an average of 1.3–1.5 m long, after which the material is additionally pressed using a roller and fed to chopper in which the rotor rotates at an adjustable speed. A large mixture of PVC, metal, glass, rubber and wood is fed to the conveyor, and then to the magnetic separator, where the metal is separated, and then the material enters the rotating metal separation drum. This mixture is classified into particle sizes<4 мм, 4–15 мм, 15–45 мм, >45 mm.

Fractions (>45 mm) larger than usual are returned for re-crushing. A fraction of 15–45 mm in size is sent to a metal separator, and then to a rubber separator, which is a rotating drum with rubber insulation.

After removing the metal and rubber, this coarse fraction is sent back for grinding for further size reduction.

The resulting mixture with a particle size of 4-15 mm, consisting of PVC, glass, fine residue and wood waste from the silo is fed through a separator to a drum sieve. Here, the material is again divided into two fractions with particle sizes: 4–8 and 8–15 mm.

Two separate processing lines are used for each particle size range, for a total of four processing lines. The separation of wood and glass takes place in each of these processing lines. The wood is separated by using inclined vibrating air sieves. Wood, which is lighter than other materials, is transported downward by the airflow, while heavier particles (PVC, glass) are transported upward. The separation of the glass is done in a similar manner on subsequent sieves, where the lighter particles (ie PVC) are transported downwards while the heavy particles (ie glass) are transported upwards. After the removal of wood and glass, PVC fractions from all four processing lines are combined. Metal particles are detected and removed electronically.

Purified polyvinyl chloride enters the workshop, where it is moistened and granulated to a size of 3–6 mm, after which the granules are dried with hot air to a certain moisture content. Polyvinyl chloride is divided into four fractions with a particle size of 3, 4, 5 and 6 mm. Any oversized granules (i.e. > 6 mm) are returned to the area for regrinding. Rubber particles are separated from PVC on vibrating sieves.

The final step is an optoelectronic color sorting process that separates the white PVC particles from the colored ones. This is done for fractions of each size. Since the amount of colored PVC is small compared to white PVC, white PVC fractions are sized and stored in separate bins while the colored PVC streams are mixed and stored in one bin.

The process has some special features that make the operations environmentally friendly. Air pollution does not occur as the grinding and air separation is equipped with a dust extraction system that collects dust, paper and foil in the air stream and feeds them to the microfilter trap. The grinder and drum sieve are insulated to reduce the occurrence of noise.

During wet grinding and washing of PVC from contaminants, water is supplied for re-cleaning.

Recycled PVC is used in the production of new co-extrusion window profiles. In order to obtain the high surface quality required for co-extrusion profiled window frames, the inner surface of the frames is made from recycled PVC and the outer surface from virgin PVC. The new frames contain 80% by weight recycled PVC and are comparable in mechanical and performance properties to frames made from 100% virgin PVC.

The main methods for recycling PVC plastic waste include injection molding, extrusion, calendering, and pressing.

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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 the use of plastic products - various films (greenhouse, construction, etc.), containers, household and large-scale packaging - is household and industrial waste.

Technological waste is subjected to thermal action in the melt, and then, during crushing and agglomeration, to intense mechanical stress. In the bulk of the polymer, the processes of thermal and mechanical degradation proceed intensively with the loss of a number of physical and mechanical properties and, with repeated processing, can adversely affect the properties of the product. So, when returning to the main process, as usual, 10-30 percent of secondary waste, a significant amount of material goes through up to 5 cycles of extrusion and crushing.

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

Reducing the amount of process waste

The amount of technological waste, primarily start-up waste, can be reduced by using heat 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 the equipment stops for a simple material in the extruder barrel or injection molding machine, it is under the influence of high temperature for quite a long time when cooling and then heating the barrel. During this time, the processes of cross-linking, decomposition and burning of the polymer actively proceed in the cylinder, products accumulate, which, after start-up, come out for a long time in the form of gels and colored inclusions (burns). Thermal stabilizers prevent these processes, making it easier and faster to clean the equipment after start-up. To do this, before stopping, 1-2 percent of the stop concentrate is introduced into the cylinder of the machine for 15-45 minutes. to a stop at the rate of displacement of 5-7 cylinder volumes.

Processing (extrusion) additives that increase the manufacturability of the process also make it possible to 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.), are precipitated from the melt onto the metal surface, creating a near-wall lubricating layer on it, along which the melt slides during molding. The use of the processing additive in the smallest quantities (400-600 ppm) allows solving numerous technological problems - reducing the torque and pressure on the extruder head, increasing productivity while reducing energy costs, eliminating appearance defects and reducing the extrusion temperature of polymers and compositions sensitive to elevated temperatures, increase product smoothness, produce thinner films. In the manufacture of large-sized or thin-walled molded products of complex shape, the use of an additive can improve pourability, remove surface defects, solder lines and improve the appearance of the product. All this in itself reduces the proportion of marriage, i.e. amount of waste. In addition, the processing additive reduces the sticking of carbon deposits on the die, fouling of sprues, and has a washing effect, i.e. reduces the number of stops to clean equipment, and therefore the amount of start-up waste.

An additional effect is the use of cleaning concentrates. They are used when cleaning casting and film equipment for a quick transition from color to color without stopping, most often in a ratio of 1:1-1:3 with polymer. This reduces the amount of waste and time spent on color changes. The composition of cleaning concentrates produced by many domestic (including Klinol, Klinstyr from NPF Bars-2, Lastik from Stalker LLC) and foreign manufacturers (for example, Shulman - Poliklin ”), as a rule, soft mineral fillers and surface-active detergent additives are included.

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. When extending the service life of the greenhouse film from 1 to 3 seasons, the amount of waste to be disposed of decreases accordingly. To do this, it is enough to introduce small amounts of light stabilizers into the film, no more than half a percent. Stabilization costs are low, and the effect of film recycling is significant.

The way back is to accelerate the degradation of polymers by creating photo- and biodegradable materials that quickly degrade after use under the action of sunlight and microorganisms. To obtain photodegradable films, comonomers with functional groups that promote photodegradation (vinyl ketones, carbon monoxide) are introduced into the polymer chain, or photocatalysts are introduced into the polymer as active fillers that promote the breaking of the polymer chain under the action 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) 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 decomposition of films increases 10 times - from 100 to 8-10 hours.

The main directions for obtaining biodegradable polymers:

synthesis of polyesters based on hydroxycarboxylic (lactic, butyric) or dicarboxylic acids, however, 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 can be said to be unlimited, but the technology and properties of the resulting polymers do not yet reach the level of the main multi-tonnage polymers;

making industrial polymers (polyolefins in the first place, as well as PET) biodegradable by compounding.

The first two directions require large capital expenditures for the creation of new industries; the processing of such polymers will also require significant changes in technology. The easiest 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 Plastpolimer developed starch-filled films with an accelerated aging period. Unfortunately, the relevance of such material then was purely theoretical, and even now it has not received wide distribution.

Waste recycling

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

Complex additives of the Siba company. Ciba, Switzerland, offers a family of complex stabilizers for the processing of various polymers - high-density polyethylene, HDPE, PP: Recyclostab / Recyclostab and Recyclosorb / Recyclossorb. They are tablet mixtures of various photo- and thermal stabilizers with a wide range of melting temperatures (50-180°C), suitable for input into processing equipment. The nature of the additives in the Recyclostab composition 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 a specific task. "Recyclossorb" is used when light stabilization plays an important role, i.e. the resulting products are operated outdoors. In this case, the proportion of light stabilizers is increased. The input levels recommended by the firm are 0.2-0.4 percent.

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

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

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

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

Complex concentrates of the Bars-2 company. For the processing of secondary polymers, SPF 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 high-impact polystyrene, are introduced in an amount of 2-3 percent during the processing of secondary plastics and, thanks to a complex of special additives, prevent thermal-oxidative aging of secondary polymers. Concentrates facilitate their processing due to the improvement of the 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 an increase in the manufacturability of the material (reduced torque and drive load). When processing a mixture of secondary polymers "Revtol" or "Revten" improve their compatibility, so the physical and mechanical properties of the resulting products also increase. The use of "Revten" allows you to increase the properties of the secondary UPM to the level of 80-90 percent of the properties of the original polystyrene, preventing the appearance of defects.

Now the development of a complex concentrate for the processing of recycled PET is very relevant. The main scourge here is the yellowing of the material, the accumulation of acetaldehyde, and the decrease in the viscosity of the melt. Known additives Western firms - "Siba", "Clarianta", allowing to overcome yellowing and improve the processability of the polymer. However, in the West and we have a different approach to the use of secondary PET. Whereas 90 percent of it is used to make polyester fibers or technical products, and the additives for this purpose are well developed, our processors are looking to bring recycled PET back into the mainstream—preforms and bottles by injection molding and blowing, or films and sheets by flat slot extrusion. In this case, the target properties of the polymer that need to be affected are somewhat different - manufacturability, formability, transparency, and the formulation of complex additives must meet the goal.

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

In countries where environmental protection is of great importance, the volume of recycling of recycled polymers is constantly increasing. Legislation obliges legal entities and individuals to dispose of plastic waste (flexible packaging, bottles, cups, etc.) into special containers for their subsequent disposal. Today, the agenda is not only the task of recycling waste polymer materials, but also the restoration of the resource base. However, the possibility of using polymer waste for re-production is limited by their unstable and worse mechanical properties compared to the original polymers. The end products with their use often do not meet aesthetic criteria. For some types of products, the use of secondary raw materials is generally prohibited by the current sanitary or certification standards. For example, some countries have banned the use of certain recycled polymers in food packaging.

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

Thus, recycled plastic products can be used to produce products that were previously made from virgin materials. For example, it is possible to produce plastic bottles from waste, i.e. recycling in a closed cycle. Also, secondary polymers are suitable for the manufacture of objects whose properties may be worse than those of analogues made using primary raw materials. The latter solution is called "cascade" waste processing. It is successfully used, for example, by FIAT auto, which recycles the bumpers of end-of-life cars into pipes and floor mats for new cars.

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

PAT

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

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

Table 1

The area of ​​their further application of recyclable PET waste is determined by their molecular weight. The molecular weight of PET is calculated from its intrinsic viscosity. Table 2 shows the range of its values ​​for various PET applications.

Table 2. Intrinsic viscosity of PET depending on the application

Obviously, the secondary polymers that underlie different types of products and, accordingly, have different molecular weights (intrinsic viscosity), require completely different recycling technologies. Recycled PET can not always serve as a basis for the re-production of original products.

Another problem of PET waste processing is related to the possible presence of PVC in them. Even with careful sorting of PET bottles, there is a chance that PVC and PE impurities will enter the composition of the recycled material. At the processing temperature of PET, PVC decomposes, releasing hydrochloric acid, which causes intense degradation of the polymer. Therefore, it is necessary to minimize the presence of PVC in the composition of PET waste. Permissible PVC content does not exceed 50 ppm.

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

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

Recycled fiber is processed into textiles or woven bases for the production of clothing and carpets. These applications can use up to 100% recycled polymer. Most often, PET fiber is used as a synthetic insulation for winter clothes or as a ready-made plush texture for sewing clothes.

PET fiber has a number of advantages over other synthetic fibers. For example, PET fiber carpets do not fade and do not require the special chemical treatment required for nylon fiber carpets. PET fibers and dye more easily than nylon. PET fiber webs made using the melt-blown technology are used for the production of noise-insulating materials, geotextiles, filtering and absorbing elements, synthetic winterizer. Finally, a small amount of recycled PET is used for the manufacture of automotive components, electrical products, and various fittings by injection molding.

Polyethylene

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

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

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

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

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

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

Cans can be produced either completely on the basis of polymer waste, or with extrusion with primary granulate. In the latter case, the sec polymer layer forms a core between the two primary polymer layers. Canisters obtained in this way are used for filling detergents by a number of companies (Procter & Gamble, Unilever, etc.).

Another example of mass production from recycled HDPE is irrigation pipes. As a rule, they are made from a mixture of secondary and primary polymers in different ratios. Given that irrigation pipes are not designed to be used under pressure, the mechanical properties of recycled HDPE are well suited for their production. The high viscosity of canister and film recycled HDPE can often be compensated for by the low viscosity of the virgin polymer, whereby impact resistance can be improved. The production of large diameter pipes from recycled HDPE is no problem either: irrigation and drainage pipes are up to 630 mm in diameter.

When using injection molding technology, the percentage of recycled plastic is lower. This technology is applied to cladding panels, municipal waste bins, etc. The cladding panel market is very attractive due to its large capacity. It is estimated that the US market alone consumes 2 billion units of sheathing panels and boards, which are still traditional lumber.

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

Polypropylene

The main source of recycled polypropylene are plastic boxes, battery cases, bumpers and other plastic car parts. To a lesser extent, packaging products made from this material are recycled. The quality of the secondary PP depends on the conditions in which the product was located during operation. The less it has suffered from external influences, the closer the properties of the secondary material to the properties of the primary. However, operating conditions are rarely so favorable. Only in rare cases can automotive plastic components be recycled in a closed loop: for example, Renault's Megane uses recycled PP bumpers to make new ones. As a rule, recycled PP is used for the production of other automotive parts that have less stringent requirements - vent pipes, seals, floor mats, etc. This example fits into the classic cascade recycling scheme.

Recycled PP is also used in various blends with virgin PP or other polyolefins in injection molding (boxes, cases) or extrusion (various profiles and semi-finished products).

Polystyrene

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

Plastic blends

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

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

Equipment

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

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

Equipment for the processing of plastic (polymers) - these are special machines and additional devices combined into a production line, which is used for processing or processing polymers (plastics) into useful and valuable materials for further use in the construction, textile, chemical, oil and other industries .

Classification of plastic recycling equipment

Depending on the functional features and purpose, all equipment for plastic processing is divided into:

1. Equipment for storage and dosing of materials/raw materials. As a rule, these are bins with devices for sorting (filtering) and unloading materials/raw materials.
2. Apparatus for transportation. They are vacuum or pneumatic.
3. Grinding and breaking machines - crushers, runners, shredders, pulpers, cavitators and others.
4. Faucets. They are used for mechanical separation of substances by means of mutual movement of particles.
5. Roll machines. Necessary for the formation (creation) of a fracture and crushing of polymer compositions.
6. extrusion equipment. With its help, polymeric materials are processed into certain products by continuously forcing the molten raw material through a forming head, the geometric shape of which determines the profile of the final product.
7. Casting machines. This is a polymer processing equipment used to make plastic compositions from powdered or granular raw materials, which are moved or squeezed in the mold cavity, where it solidifies and, after cooling, is removed.
8. Machines for extrusion blow molding. They, according to the method of forming a product from a blank, are divided into inflatable, extrusion and injection mechanisms.
9. Vulcanizing machines and presses. There are continuous or periodic action and are used to create products from powdered or granular raw materials.
10. Coating and impregnating machines. Are applied to drawing polymeric coverings on a special substrate.
11. Washing complexes. Necessary for preliminary purification of the polymer after granulation or grinding, but before its processing.

Plastic recycling machines

The main machines from a large number of varieties of special equipment for polymer processing are the following units:

• crushers - the unit operates on the principle of a blender, cutting whole products into small pieces;
• agglomerators - in them, small pieces of polymer are subjected to even greater crushing, and then sintering into small lumps;
• granulators - with their help, the mixture obtained from the agglomerator is heated and cut into granules.

Less important, but still necessary, the following plastic recycling equipment is considered:

• washing line units;
• transport nodes;
• different types of separators;
• dryers.

Equipment for starting a mini-factory

In order to run a small plastic recycling plant, the following polymer processing equipment is required.

1. Basic equipment:
   • crusher or shredder;
   • agglomerator;
   • if necessary, a granulator.
2. Optional equipment:
   • hot wash bath;
   • 1-2 centrifuges;
   • extruders for recycling;
   • sieve substitutes;
   • mixers and dispensers;
   • flotation washing;
   • connecting units (pneumatic or vacuum transport).
   • control module.

Major manufacturers of aggregates for polymer processing

The most demanded manufacturers of plastic recycling equipment are the following companies:

European.

1. HGMA Wulf GmbH is a German manufacturer with an excellent reputation, which manufactures not only equipment for the primary and secondary processing of polymers, but also earthmoving and construction equipment.
2. Global Tech is a Polish company that makes fast and reliable stationary and mobile crushers.
3. Herbold Meckesheim is an excellent German manufacturer of aggregates for the entire plastics processing and recycling cycle.

Chinese.

1. China IS-MAC Machinery is China's largest manufacturer of extrusion equipment for the processing of plastic bottles and other plastics.
2. LISHENG INDUSTRIAL is a manufacturer of washing machines, crushers, printing machines and other equipment.
3. Blue Ocean - manufactures extrusion machines and injection molding plants.

Russian.

1. GK Polymer System Group (Novosibirsk) - produces everything necessary for the processing of polymers.
2. ENGEL Austria GmbH (Moscow) - makes injection molding machines for plastic injection molding, rubber / silicone processing units, etc.
3. StankoPet (Moscow) - produces almost the entire range of equipment for plastic processing.

Profitability of polymer processing equipment

A rough estimate for completing a small polymer processing plant will include the cost of:

• purchase of a line of equipment for processing plastic bottles - about $ 10,000;
• transportation and installation of equipment - up to 15% of the cost of equipment ($1,500);
• wages to employees - about $ 7,000;
• rent (+ repair) of the premises - $ 10,000;
• other events - $5,000.

At the same time, a ton of recycled plastic costs about $750, while the purchase of raw materials will cost $100 per ton.
The indicated level of investment is calculated for a mini-factory with the purchase of equipment for the processing of plastic bottles and similar polymer products with a capacity of 1 ton per day, i.e. with an income of 7,000 to 9,000 dollars a month. With such a payback, the plant will begin to generate net profit in the second year of its operation (in 15-20 months).

It should be clarified that the payback period, as well as the cost of opening a plant, may be less if:

• preferences will be received from the state;
• the plant will be opened near the place where plastic is sorted for further processing;
• the plant will receive gratuitous investments from international funds for the protection of nature.

Receipt of raw materials and their marketing

Depending on the production line and the wishes of the owner, the plastics processing plant can produce granular or powdered polymer raw materials. The marketing of such products, as a rule, is not something difficult, since they are in great and constant demand in the following areas:

• production of nonwoven materials;
• production of building materials;
• production of polymer products for national use;
• production of chemical fibers;
• as an additive to primary raw materials (reduces the cost).

Factories with appropriate production lines are widely represented in all regions and are in dire need of cheap raw materials.

In addition, the polymer processing line can be extended with additional equipment and already independently produce some types of plastic products. For example:

• packing nets for vegetables and fruits;
• garbage bags;
• packages;
• furniture fittings;
• polymer tiles;
• various pipes, molds, parts for plumbing or sewerage;
• accessories or technical details for cars;
• liquid storage containers;
• other small polymer products.

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

Environmental conditions dictate the need for waste-free production of polymer-type goods in order not to pollute the ecology of the surrounding space. For this reason, industrial production annually increases production capacity due to the secondary and subsequent processing of polymers.

Agglomerators, as a result of functioning, transform 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 material is reused in the production of polymer products, in the form of a main or auxiliary element.

Polymer processing technology

The processing of polymers involves preliminary operations in the sector of the unit, with the help of appropriate knives. Further, the processing of polymers continues with heat treatment (under the influence of a high temperature regime, frequent contact of crumbs of polymeric raw materials occurs).

Upon receipt of operating temperatures up to 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 gate valve, are transferred to the tank chamber for temporary storage and subsequent removal.

Granulators are devices that are used for. Granular processing of polymers is achieved by micro-crushing operations and the formation of the same type of polymer or plastic granules. The resulting granulate is used as a feedstock in the manufacture of cast and extruded polymeric substances.

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

Equipment for polymer processing

For secondary operations, polymer processing provides for equipped directional mechanisms - crushing and grinding production lines. With their help, a preliminary preparatory process of used polymer products for extrusion and sintering operations takes place. There are three types of different capacity crushing lines.

Depending on the technical equipment of the model used, the grinding devices can carry out the functions of screening, for separating small-sized elements, automatically washing and drying polymeric materials. They are also equipped with conveyor movable belts, metal detectors, noise protection, which greatly simplifies the process of processing the secondary polymer mass.

Recycling of polymers is also an environmentally friendly activity that requires the cost of 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 a guarantee of an excellent result, obtaining a quality product in the form of feedstock for further use in the production of polymer products.