Over the past 10-15 years, plastic materials have formed a wide range of areas in which products of their processing can be used. Synthetic material itself is currently undergoing a period of radical technological changes, as a result of which the building materials market is filled with new offers. Suffice it to note the family of composites that displace both metals and wood.
In turn, plastic processing as a way to obtain a fundamentally new and, most importantly, more advanced material in terms of performance, is not so interesting. Using the technology of this type, you can recreate the old synthetic structure. Nevertheless, this area of activity of processing plants is justified for many other reasons, including environmental and financial ones.
Types of plastic waste
Technologists distinguish 4 categories of plastic waste that can be recycled. First of all, these are single-grade plastics in the form of scrap and directly waste, which can be added to masses that are similar in chemical composition. The second category is contaminated single-grade plastics, the processing of which requires the initial implementation of treatment technological measures. The third group is represented by mixed plastic waste containing foreign impurities.
In fact, third-party particles are the same contaminants, metal or cement elements that require pre-treatment. Also, the theoretical foundations of plastic processing include the allocation of a group of different - grade plastic materials. In this case, not only plastic and third-party particles of other industrial or building materials are mixed, but also different structures of the plastics themselves.
Classification of processing methods
The main classification provides for the allocation of technology for direct molding of products and molding of semi-finished products. As for direct processing, this group includes polymerization methods, contact molding, broaching and wet winding, as well as spraying. Methods of molding plastic products from semi-finished products are also popular. In this area of technological development of processing include injection methods, extrusion, molding from prepregs and premixes. Plastic processing is also physicochemical and mechanical.
Almost all mechanical processing methods are focused on grinding treated waste, followed by obtaining a homogeneous mass. An important difference between this group of methods is the fact that the resulting product does not differ in its physicochemical properties from primary raw materials. On the contrary, physicochemical methods are based on technologies for the destruction of the structure of the primary material, during which the operational qualities of the obtained substance also change.
Shredding plastics as preparation technology
This is a common operation in the processing industry, which is used not only in plastics. Depending on the requirements for the final fraction, the corresponding units are connected to the work. Universal grinder can be called compactors with auger organs of mechanical impact.
In the process of work, the loaded plastic mass is compacted with the help of disk granulator plates with friction mechanisms. As a rule, two plates are used, one of which remains stationary. Shredding processing of plastic waste largely depends on the characteristics of the material itself.
For hard raw materials, crushers and aggregates equipped with cutters of various shapes are used. Work with plastic waste in the form of a film is performed by more delicate methods. For example, on a complex line, which includes units of compaction, grinding and granulation. In this case, the knife elements directly perform the mechanical grinding task.
Waste separation technologies
In part, this stage is associated with preparatory treatment activities, which were mentioned above. But the separation process as such is more extensive and is not limited only to cleaning from dirt. It is also important to carry out separation after grinding, since small granules are easier to separate from foreign particles. So, the primary separation still involves the separation of pieces of plastics from metal. For this, magnetic and electromagnetic coils are used inside the drum rotating structures into which the target material is loaded.
During rotation, small elements of non-ferrous and ferrous metal lag behind plastic and are discharged through special channels. It turns out the initial processing of plastics, increasing the uniformity of their composition. However, with such separation, some of the plastics themselves are lost. As a rule, the share of loss does not exceed 1%. Industrial containers for washing are used to remove impurities. Shredded particles are washed under a stream of water, which is supplied under high pressure. Sometimes to increase the effectiveness of the procedure, solvents are added to the water.
Individual processing
The individuality of processing is due to the fact that only sorted plastic gets into the working area, including those ready to be mixed with suitable masses in structure. Processing itself is carried out in different ways, but extruder is considered the main one. A special installation with screws and a loading hopper receives crushed plastic, melts it and feeds it through an extruder to the production line. At the final stage of release, depending on the machine, the operator can change the parameters of the release of plastic. The degree of compression of the raw material is also regulated, which also makes it possible to choose the optimal length of the worm in order to ensure sufficient homogenization.
Such plastics processing is considered sparing, from the point of view of maintaining the operational properties of the material, but this does not mean that it can be repeated endlessly. The fact is that the same plastic substance using this technology can be processed no more than 3-4 times depending on the conditions of use. Subsequently, the mass is sent to recycling lines with deeper chemical processing.
Plastics processing technology without separation
The exclusion of the stage of separation and treatment of plastic wastes led to the specifics of the technology for their further processing. Usually, melting machines with additional equipment for calendaring the material are used for this. As a result, ready-to-use panels, plates and sheets of plastic are fed to the exit . This is a coarse material with a rigid structure, which contains a large coefficient of impurities. Due to the content of third-party particles, the quality of the plastic and the environmental cleanliness are reduced. On the other hand, the processing of plastics without separation is not expensive and in some areas provides a material that is optimal in terms of technical characteristics.
Cast processing
In order to optimize the processing process, another way to reduce the cost of production was developed. Multicomponent casting technology is an option for manufacturing combined products. Its essence is that through several levels of molding a three-component product is created. It is based on cheap plastic based on the same unpurified substances, and then comes the level of average quality mass. In turn, the outer layers are a completely clean environmentally friendly composition for which extruder processing of plastic was used.
The production of plastic materials based on multicomponent molding is carried out by a technique that ensures the passage of waste through several channels. By the way, plastics are not always used for internal layers. They are often replaced by cheaper material, which includes barium sulfate, talc, ceramics, etc.
Plastic waste modification
It is not at all necessary that processing should be oriented towards obtaining the same operational and structural properties that the product was previously characterized. This stage opens up wide possibilities for modifying the structure by introducing special additives. For example, the recycling of plastics with the addition of an ethylene copolymer helps to increase resistance to mechanical stress and elasticity. If such an inclusion is introduced into the structure of polyvinyl chloride, then it is possible to count on an increase in impact resistance.
Processing equipment
There are not so many specialized machines designed to perform full cycle processing. In Russia, for example, the Reverzer installation from the Japanese company Mitsubishi is known. This is an example of the same extruder machine equipped with screws and a degassing device. The English plastic processing equipment is also well known to domestic enterprises, the advantages of which are demonstrated by EPG installations. This is a company that offers innovative ways to recycle blown waste.
How to choose the best processing method?
To begin with, the tasks that will already be facing the released products should be evaluated. This will initially determine the need for separation, and with the possible use of modifiers. The simplest and cheapest method is the undivided processing of plastic products, which allows you to get high-quality fencing, flooring materials, insulation panels, etc. The technology for processing cleaned plastics is usually oriented to the subsequent release of plastic containers.
Conclusion
The synthetic waste processing industry today is especially relevant and in demand in various industries. Getting inexpensive and practical raw materials at low cost is the main motive that guides the participants in this market. At the same time, in Russia this sector of industry is not yet as developed as in Europe. Of the most developed, it is possible to distinguish only the Plarus plastic processing plant, which has been operating since 2009. The technological features of this enterprise include the use of the modern method of processing PET bottles. At the same time, other enterprises are also gaining momentum, each year increasing the output of recycled plastic in various forms.