Due to their unique physicochemical, technological and consumer properties, polymeric materials are widely used in all spheres of modern society. Particularly promising is the use of certain types of synthetic resins (polyester, epoxy), which do not require sophisticated equipment and significant energy costs. But at the same time there are harmful volatile substances (phenol, ethylene glycol, acetone). To reduce harm, it is advisable to carry out all stages of the process in sealed containers. This is not always possible.

For example, in order to quickly and accurately fill the form (porous frame), it is necessary to introduce an additional amount of solvent (plasticizer), which has an increased volatility and toxicity. You can eliminate this disadvantage by using vibration at a frequency of 50-200 Hz. To ensure high flowability of viscous mixtures without the use of a plasticizer, it is necessary to know the range of natural frequencies of oscillations of the filler elements, fittings and forms that play the role of a resonator. Vibration may be superficial or bulk. At the same time, different vibrational frequencies can be used at different stages of the process: at the filling stage, to create resonant vibrations of the form elements, then to degass the mixture and accelerate the hardening process, the oscillation frequency is increased to hundreds of hertz. If external heating is carried out in the manufacture of large parts, this is accompanied by uneven temperature by mass, which worsens the environmental conditions of the process.

The greatest intensification of production in the manufacture of powder parts is achieved by cold extrusion of the part from sintered powder blanks and cold forming of the powder in a closed matrix, followed by sintering.

The first technological process requires first the preparation of powder batch (from plasticizer, alloying elements), from which in a closed die a blank of a simple form with a porous structure is formed. Then this billet is sintered in a reducing atmosphere (hydrogen, ammonia) or an atmosphere that does not allow oxidation (argon, nitrogen). After sintering, this billet became a solid, which is subjected to subsequent cold stamping by extrusion (similar to a conventional billet, cut from a cylindrical rod). Now the part is subjected to heat treatment in a protective atmosphere (annealing, quenching).

The second type of technological process for the production of high-density powder parts consists in forming a part of the required shape immediately from the prepared powder mixture in a closed matrix, which is subsequently subjected to sintering in a protective atmosphere and, if necessary, quenching.

Plastics are materials based on natural or synthetic polymers that can be molded into products of complex configuration under the influence of heat or pressure and then stably maintain their shape. Depending on the technological process of production, the filler used and the binder (resin), plastics can be composite, layered or cast, and by the nature of the resin used – thermosetting or thermoplastic.

In the production of plastics in the processing of polymeric materials, gaseous products, organic acids, phenol, styrene are released. To localize the released substances it is necessary to provide local suction from the equipment with their connection to exhaust ventilation systems. During the processing of thermoplastic materials, solid waste accumulates (ingots and pieces of polymers, sprues, trimming, products with defects), which can be completely recycled on the crushing equipment and reused as secondary raw materials in the form of additives to the main production. But this produces almost the same amount of waste that cannot be used. Plastics are little used as secondary raw materials due to the diversity of their types and the complexity of their compositions. The production of plastics is not associated with pollution of wastewater, as the technology must be provided with recycled water supply.

The main directions of recycling and disposal of plastic waste are as follows:

– burial at landfills and dumps;

– processing them by factory technology;

– incineration together with MSW and industrial waste;

– pyrolysis or separate burning in special furnaces; ;

– the use of waste plastics as a finished material in other technological processes.

The best way to use waste plastics is to recycle them using factory technology. With a variety of recycling methods, the overall process can be represented as shown in the figure below.

The first stage involves the separation of non-plastic components and the sorting of waste by appearance. At the second stage, the grinding of plastic waste (in several stages) to a size sufficient for further processing is performed. The third stage provides washing of the crushed waste from pollution of organic and mineral character. The fourth stage is determined by the method of separation of waste by types of plastics: if it is a wet method, then the waste is first classified, and then dried; using dry methods, the first shredded waste is dried and then classified.

Dried crushed waste is mixed, if necessary, with stabilizers, dyes, fillers and granulated. Sometimes at this stage the waste is mixed with the product. At the final stage of the process, the granulate is processed into products. This stage is similar to the initial processing process, but sometimes requires a specific approach to the choice of operating modes of the equipment.

With high-quality pre-sorting of plastics by type, achieving a high degree of purification and isolation of individual waste from mixtures, their processing practically does not differ from the processing of primary plastics. At the same time, it is necessary to take into account the ability of polymers to preserve or change properties in the process of multiple processing, which generally determines the feasibility of processing waste. The change in the physicochemical properties of most polymers during repeated processing is associated with a decrease in the molecular weight of plastics and the branching of their structure. A decrease in the molecular weight of plastics leads to a change in their strength properties.

For the processing of waste by injection molding, machines using the type of intrusion with a constantly rotating auger are usually used, which ensures the spontaneous capture and homogenization of waste.

A feature of the recycling of polyvinyl chloride (PVC) is the need for its additional stabilization. Soft PVC waste is used to produce household products, film coatings and films. In this case, 20% of the waste is crushed on the mixing rollers, mixed with commercial PVC, dyes, lubricants and a stabilizer, and then passed through a system of heating and finishing rollers. Waste bags, pipes, household buckets, sealing profiles and gaskets are produced from high-pressure polyethylene waste. Polypropylene waste is processed into textile spools, plumbing parts, door handles, plant boxes.

Disposal of waste mixtures without prior separation of their components makes the recycling process cheaper, but the physical and mechanical properties of the resulting products are much worse.

Multicomponent casting is used more and more widely for the use of waste plastics, in which the product has an outer and an inner layer of various materials. The outer layer of the product is made of high quality plastics and has an excellent presentation, and the inner layer is usually not subject to high requirements even for physico-mechanical parameters, so this layer includes cheap fillers (talc, barium sulfate, glass and ceramic beads ). This significantly reduces the cost of products (usually furniture and household items).

Promising is the use of waste plastics as a finished material in a number of industries:

– waste synthetic fibers and nonwovens are used for sorption treatment of industrial wastewater;

– bitumens are used in construction, asphalting, and the use of waste polyolefins in a composition with bitumen is a direction that allows to modify the properties of coatings.

There is a mass of modern effective ways of utilization and recycling. But it is still difficult to talk about any fundamental changes taking place in this area in our country. As for European countries and the United States, people there have long concluded that the resource potential of MSW should not be destroyed, but used. All progressive humanity is aware that it is impossible to approach the problem of MSW as a fight against garbage, setting the task at all costs to get rid of it.

D.S. Lipchansky
VI All-Russian Scientific and Practical Conference
“Progressive technologies and economics in mechanical engineering”