Recycling of Waste Plastics to Reduce Environmental Pollution

2021-11-04 14:29:47

Plastic products have brought convenience to the people but also caused a tremendous negative impact. As the output of plastics increases year by year, the prevention and control of waste plastic pollution have become an environmental issue of global concern. Plastic products are difficult to degrade, and the generated plastic fragments and plastic microbeads cause severe environmental pollution, thereby endangering human health. In the natural environment, waste plastic will be broken down into smaller pieces, which seriously threatens fish reproduction and the environment they depend on. Microplastics themselves contain plasticizers and other additives, many of which are toxic and harmful substances. The ingestion of plankton, fish, shellfish and other trophic organisms will seriously affect their growth, development, and reproduction. After fish accidentally eat the microplastics, humans consuming these fish products will severely impact human health.

 

International Actions for the Prevention and Control of Waste Plastic Pollution

At the first United Nations Environment Conference held in Nairobi on June 23-27, 2014, the resolution on "Marine Plastic Waste and Microplastics" was passed, and plastic waste pollution was listed as one of the top ten environmental problems in the world that need to be solved urgently. Two reports released on the same day pointed out that a large amount of plastic garbage in the ocean is increasingly threatening the survival of marine life. At the second United Nations Environment Conference held on May 23-27, 2016, the resolution of "Marine Plastic Garbage and Microplastics" was again passed, and microplastics pollution was listed as the second-largest scientific issue in the field of environmental and ecological science research. . At the 3rd United Nations Environment Assembly held on December 4-6, 2017, the resolution of "Marine Plastic Garbage and Microplastics" was also passed, which mentioned that the amount of marine plastic garbage is significant and increasing rapidly. , Ecosystems, animal welfare, fisheries, marine transportation, leisure, and tourism, local social and economic adverse impacts will increase, and there is an urgent need to strengthen the number of microplastics and Nano plastics and their effects on marine ecosystems and oceans. Understanding of product and human health effects. The resolution encourages all member states to formulate and implement action plans to reduce marine litter and microplastics, and promote resource efficiency, including improving the collection and recycling of plastic waste, as well as redesigning and reusing products and materials, and avoiding unnecessary plastics And the use of plastic products containing particular chemical components.

Reuse of Waste Plastic

The Norwegian government is actively advancing the prevention and control of marine plastic pollution, proposing to explicitly include plastic waste in the scope of the Basel Convention and include it on the agenda of the eleventh meeting of the Open-ended Working Group of the Geneva Basel Convention held in September 2018. Proposed the establishment of a new partnership in plastic waste and its possible terms of reference to reclassify plastic waste. Austria also supports work in this area. Uruguay proposed to implement the plastic limit order within one year. Kenya also announced a ban on plastic bags in the packaging industry in 2017 and completely stopped importing, manufacturing, and using them.

On June 19, 2012, in Rio, led by the United Nations Environment Programme, governments, industry representatives, and United Nations agencies initiated the establishment of the Global Partnership for Marine Litter (GPML) to address the impact of marine debris on the environment, livelihoods and humans. Damage to health. The US government has banned microplastics in cosmetics and toiletries; the European Union plans to invest 550 million euros in remediation of marine pollution; the UK has decided to ban the use of microplastics in cosmetics and toiletries from 2017. The Canadian Federal Government issued an official gazette prohibiting the sale of cosmetics such as shower gel, toothpaste, and massage cream containing plastic microbeads. South Korea and other countries have also banned plastic microbeads in cosmetics and personal care products.

 

Waste Plastic Recycling Technology

There are three standard methods for waste plastic treatment: recycling, co-incinerating with domestic waste, and sanitary landfill.
There are two main technical approaches for recycling:
①. Single-type plastic polymer recycling technology. Regenerate waste plastics into the same kind of raw materials.
Single plastic polymer recycling technology means that different types of plastics such as polyethylene (PE), polypropylene (PP), polyester (PET), polystyrene (PS), polyvinyl chloride (PVC), etc., are processed in different ways. Process, separate recycling, and reuse, including regeneration technology, physical modification technology, chemical modification technology, etc.

②. Multi-type plastics are generally made into other raw materials that can be used comprehensively or recycled energy.
Multi-category plastic polymer utilization technology comprehensively disposes of plastic product waste with complex components. It is difficult to separate to maximize the overall effect, including degraded utilization, fueling, and cracking technologies.

Direct Reuse of Waste Plastic
After the waste polyurethane foam is crushed according to a specific size requirement, it is used as the packaging container's cushioning filler and carpet lining material; or the waste polyvinyl chloride products are crushed or directly extruded used for the wire protection tube in the building.
Different types of plastics have other recycling methods and use (see Table 1).

plasticRecovery methoduse
PE polyethyleneMelt granulation and regeneration; catalytic cracking to produce fuel oil; processing into wood-like composite materials
Melting, granulation
PE recycled pellets can be used to produce agricultural films, plastic greenhouse materials, industrial packaging films, lactic acid beverage bottles, etc., and can also be used to make fertilizer packaging bags, garbage bags, agricultural reclaimed water pipes, and trees.
Wooden supports, barrels, geotechnical materials, etc.
PVC polyvinyl chlorideMelting, granulation
Pyrolysis and recovery of vinyl chloride
Plastic door and window profiles, pipes, building materials, etc.
PP polypropyleneExtrusion; Catalytic cracking to produce fuel oil
Thermal decomposition to produce benzene, toluene and xylene
According to the quality, it can be used to make water buckets, trash cans, baskets and food containers for microwave ovens, woven bags, packing belts, ropes, etc.
PS polystyreneCrushing, pelletizing, regeneration; modified production of adhesives, quick-drying paints, and waterproof coatings
Pyrolysis to prepare styrene monomer
Used to make building materials, stationery, rollers, and cup boxes or disposable tableware for fast-food stores
PET polyethylene terephthalateGranulation, regeneration; ethylene glycol/methanol decomposition to produce dimethyl terephthalateCoke, Sprite and other tea beverage bottles; used as pillow cores, mattresses, sleeping bags, felts, etc.; glass fiber reinforced materials, with good heat resistance and mechanical strength, can be used to make auto parts

Table 1 Recycling methods and uses of different types of plastics

 

Waste Plastic Modification and Recycling Technology

Thermoplastics are plastics that can be softened by heating and hardened by cooling within a fixed temperature range and processed repeatedly, such as polyvinyl chloride, polyethylene, polypropylene, polystyrene, ABS plastic, etc. Such waste plastics can be recycled if they can be sorted and recycled, and the quality of their products can basically reach the level of the original products, and the performance of their recycled products can be improved through physical and chemical modifications.

Physical modification refers to the mechanical blending of recycled materials, other polymers or additives, so that the mechanical properties of recycled products are improved, as a higher-grade recycled product.

The Physical Modification Includes:
①. Filling modification, adding fillers to recycle waste plastics, increasing the shrinkage of products, improving heat resistance, etc. The essence is to mix waste plastics with fillers so that the mixed system has good performance;
②. Strengthening modification, adding glass fibers, synthetic fibers, and natural fibers to enhance the strength and other properties of recycled plastic waste products;
③ Toughening modification, using elastomers or blended thermoplastic elastomers and recycled materials for toughening modification, shortening the cycle of plastic material preparation and product production, and improving the comprehensive mechanical properties of recycled plastics.

 

The Chemical Modification Includes:

①. The chlorinated modification that is, chlorinating polyolefin resins to obtain chlorinated polyolefins with different characteristics due to different chlorine content, which can be made into products with good characteristics such as flame retardant and oil resistance;
② Cross-linking modification, by cross-linking polyolefin waste, can improve its tensile properties, heat resistance, environmental resistance, dimensional stability, abrasion resistance, chemical resistance, etc.;
③. Graft copolymerization modification, including grafting, block copolymerization, etc., grafting monomer can be used to graft polypropylene through a certain grafting method, and its basic properties are similar to polypropylene. The purpose of graft-modified polypropylene is to improve the adhesion or compatibilization between polypropylene and metals, polar plastics, and inorganic fillers.

 

Comprehensive Utilization

Thermosetting plastics cannot be softened or cured under certain conditions when exposed to heat and then cannot be recovered into plastic products. Phenolic plastics are often used in construction materials. They have excellent electrical insulation and mechanical properties, sturdiness, and durability, and the molding size is not easy to change. They are suitable for the production of various laminates, glass fiber reinforced plastic products, and coatings.
This type of waste plastic is often regenerated through degradation, or made into low-quality plates, or used as fuel.

This type of waste plastic is often regenerated through degradation, or made of low-quality sheets, or used as fuel. Plastic recycling line has become the first choice. In developed countries, due to its advanced heat recovery equipment and technology, high combustion efficiency, and better pollution control, The recycling of waste plastic thermal energy has become an important utilization method, reaching the level of large-scale commercial application. The use of thermal energy to treat waste plastics can save complicated work such as preliminary sorting and can process waste plastics and household garbage in large quantities, but the operating costs are relatively high, and the equipment costs are also high.

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