Third, plastic packaging waste recycling
Plastic packaging materials have the advantages of light weight, high strength, good impact resistance, transparency, moisture resistance, aesthetics, stable chemical properties, good toughness, and corrosion resistance, and they have widely replaced a large amount of metals, wood, paper, glass, etc. in the packaging field. Leather, etc. Therefore, plastic packaging has played an irreplaceable role in alleviating China's resources and energy pressure. However, a deadly weakness of plastic packaging materials is that they are naturally degraded for longer periods, some for more than 100 years. The non-degradability of plastics leads to the long-term existence of waste. Moreover, they are often discarded after they are consumed. Therefore, plastic packaging waste has become a more and more prominent environmental issue. The so-called â€œwhite pollutionâ€ has formed, which has caused great pressure on the living environment of human beings. Therefore, plastic packaging waste has become Recycling is imminent.
Plastic packaging waste recycling technology can generally be divided into four kinds of recycling and reuse technology, mechanical processing and recycling, energy recovery incineration and landfill technology.
Recycling is the most active way to promote the recycling of materials. It is an effective recycling method that protects resources and protects the ecological environment. This method can be divided into three methods: recycle recycling, composite recycling, chemical treatment, recycling and recycling.
(1) Recycling cycle reuse
Recycling reuse refers to a process that is no longer processed, but is reused directly after cleaning. This method is mainly for some hard, smooth, clean, easy to clean larger containers, such as trays, turnover boxes, large boxes and large-capacity beverage bottles, barrels containing liquids. These containers can be used after they have been technically processed and passed the hygienic test. The technical treatment process is as follows: First, it is classified and selected, followed by basic requirements, followed by washing â†’ pickling â†’ caustic washing, disinfection â†’ washing â†’ sodium sulfite soaking â†’ washing â†’ distilled water washing â†’ drying at 50Â°C â†’ reuse.
(2) Composite regeneration technology
Discarded plastics are generally mixed with different types. When the separation is difficult or uneconomical, they are directly molded in a mixed state. Flange melting machines and vented extruders are generally used. These methods have been put to practical use. Polyolefin-based mixed plastics, commercial production of piles, wood and other products. Even if selected, incompatible resins are mixed together, their performance will be affected, which is one of the problems of composite regeneration. Therefore, recent studies on the application of compatibilizers are quite popular and practical. When plastics with poor compatibility are mixed together, adding a compatibilizer can achieve the purpose of not reducing the performance. Another problem with the recycling of hybrid plastics is the appearance of recycled materials, which have a low degree of color freedom, and the general colors are gray to black, so their use is limited and only low added value products can be made. To break this limitation, consider using a composite layer molding: the middle layer is a reclaimed material, and the inner and outer layers are new materials, and their quality and appearance are not inferior. For example, a three-layer film, a three-layer sewage pipe or a surface layer of a new resin, and an inner layer of a plastic window frame for a recycled material. These are already under development.
(3) Chemical treatment recycling
The chemical regeneration method converts a polymer into a monomer or polymer short chain through pyrolysis, hydrogenation, or chemical reagents, and converts it into oil, monomers, and chemical raw materials. In addition, it is also possible to use waste plastics in the blast furnace to produce carbides as components required for steelmaking. Compared with the mechanical method, it has the following advantages: The chemical raw material produced by decomposition can be comparable to the new material, and the mechanically recycled polymer has various degrees of degradation; in addition, it has the potential to deal with waste in a large amount and can be realized again. Recycling, in turn, can actually control the pollution of plastic waste to the environment. Although the chemical recovery and regeneration is not novel from the perspective of the reaction mechanism, there are still many engineering and technical problems to be solved before all of them are put into practical use.
With the in-depth study on the recycling and utilization of packaging waste plastics, more and more new technologies will continue to emerge. I have used the recycled packaging waste PE to modify the asphalt in order to improve the weather resistance of the asphalt and make it specialized. Paving on high-grade pavements can not only save energy, protect the environment, alleviate the â€œwhite pollutionâ€ problem that afflicts humanity, but also improve the low-temperature use performance of high-grade highways, taking into account social and economic effects.
2, mechanical processing recycling
Mechanical treatment and reuse include direct regeneration and modified regeneration.
1 Direct recycling
Direct recycling refers mainly to waste plastics, which are directly plasticized after crushing in the early stage, followed by molding and granulation. Direct regeneration can be divided into three types based on the source and use of waste plastics: 1 It is not necessary to perform the preliminary treatment such as delivery, cleaning, and direct plasticization after crushing. This method is mainly used in the production of packaging products scraps and residues, they can be directly sent to the hopper and the new material at the same time, without any pre-treatment; can be used although it is used, but very clean, without any pollution Plastic containers and so on. 2 It must be separated and washed, dried, broken and other pre-processing. In particular, for contaminated products, first coarse washing, removing sand, stones, metals and other impurities to prevent damage to the machine; then centrifugal dehydration, and then sent to the crusher, and then finely washed to remove the internal impurities of the package. After washing, it is dried and directly plasticized or granulated. Its object is generally a variety of uses and shapes of packaging containers, pockets, films and the like. 3 to be specially pre-treated. If PS foam is bulky and difficult to put into processing machinery, it is necessary to perform defoaming and volume reduction beforehand.
2 modified regeneration
The purpose of modification and reuse is to improve the basic mechanical properties of recycled materials to meet the needs of the quality of recycled products. The methods of modification are divided into three categories: one is physical modification, that is, through the mixing process, it is usually possible to carry out the modification and modification of activated inorganic particles, the toughening modification of waste plastics, the reinforced modification of waste plastics, and the recycling of plastics. Alloying and other processes to prepare composites and multi-component copolymers; the other is chemical modification, that is, through chemical crosslinking, grafting, blocking and other means to make changes in its molecular structure, change the material properties, so as to obtain better The special properties. There are many chemical modification methods, but the most essential one is to chemically react on the old macromolecular chain or between chains, that is to say, rely on reactive groups on the molecular chain or chain ends to react again, or on the chain. Attaching a certain characteristic group or connecting to a characteristic branch or reacting between the macromolecular chains to form a crosslinked structure results in the structural degeneration of the old polymer, which leads to the change and improvement of its properties. The third category is physical chemical modification. Its technological process and characteristics are in a specific screw extruder, so that a variety of components of the material in the physical blending modification at the same time, chemical graft modification; after the modification is further strengthened Mix and granulate or shape directly at a specific temperature. This is an integrated system that integrates grafting, cross-linking and blending. Its advantages can shorten the time and production cycle of the modification process, make the production continuous, and can obtain more effective modification effects.
3, energy recovery incineration
Incineration is the simplest and most convenient way to dispose of waste plastics and waste. It uses the mixture of miscellaneous plastics and other waste that cannot be used for recycling as a fuel, incinerates it in an incinerator, and then makes full use of the heat generated by combustion. The most important feature of this method is to convert the material that has been identified as waste into energy. Its heat output can reach 5 234-6 987 kJ/ton, which is basically the same as other fuel oils. It is much higher than that of paper and wood burning, and it has obvious capacity-reducing effect. Its quality can be reduced by about 85%, and its volume can be reduced by about 95%. The residue after combustion is small
Due to its high density, landfills are very small and easy to use, stable at the same time, and easy to disintegrate in the soil.
The incineration process is very simple and no pre-treatment is required. Waste can be transported directly to the furnace, saving manpower resources and obtaining high-value energy, effectively protecting the ecological environment.
Landfill is one of the simplest ways to dispose of waste plastics. It is to dispose of waste plastics in wastelands or hollows in the outer suburbs to decompose them. The disadvantages of landfilling are obvious: (1) Landfilling means losing all available resources; (2) Due to the small specific gravity and large volume of plastic waste, the space and area occupied by landfilling are large; (3) Plastic waste is difficult to degrade, and it will hinder the reuse of landfills (for example, all kinds of plants cannot grow); (4) Precipitation of additives in plastics can also contaminate soil and water resources.
Although the landfill method is the last resort method, it still has a certain role. Because this method does not require equipment, do not invest, the method is relatively simple. Moreover, after the waste is buried deep, it will not cause damage to the plants on the surface in the short term, and the state of pollution can be suspended. At present, many research institutes abroad have been working on the research and development of microorganisms or enzymes that can break down plastics. According to reports, the Institute of Life Science and Industry of Japanâ€™s Ministry of International Trade and Industry discovered two new strains of bacteria that can decompose plastics, which can degrade 0.2% of polyvinyl alcohol in four days and degrade polyurea formaldehyde resin by 30% in two weeks. Therefore, if a certain microorganism can be introduced into a landfill to degrade plastic, it will be an effective way to solve the plastic waste.
(Author/Fang Changqing Tang Wang)
Source of information "Guangdong packaging"
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