Review on the recycling process of the hottest pla

2022-09-23
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Summary of recycling and regeneration process of plastic packaging waste

the increase of commodities also brings about the increase of packaging waste, in which plastic materials occupy the first place. Only by recycling or reusing these plastic packaging wastes can we solve the pollution problem brought by these wastes to the surrounding environment

with the development of economy, people pay more and more attention to packaging. Now the packaging of products has become an indispensable part of commodities. Plastic has good physical and chemical properties, good mechanical properties, easy modeling, good printability and other advantages, and has become the first choice of packaged goods. At present, the annual output of plastic manufacturers in the world exceeds 100 million tons, and packaging accounts for more than 30% of the whole market

the key to the rapid development of plastic packaging is that it exceeds all materials today in the performance price ratio of materials, but after the use of goods, the packaging is discarded. From the perspective of its recycling, this material is not easy to recycle and decompose, and a large number of waste plastics will cause serious pollution to the social environment, which will also lead to many serious social problems. Plastic packaging waste has accounted for more than 85% of waste plastics. Therefore, recycling and recycling technology has also attracted more and more attention

the treatment methods of plastic packaging waste can be basically divided into landfilling, incineration and recycling

landfilling

landfilling method is simple, does not need investment, does not need any equipment, and will not pollute the surface or harm the surface vegetation after deep burial, which can solve the environmental pollution of this material as soon as possible. It calls on the state to strengthen the construction of the utilization standard system, but this method will occupy a lot of land for a long time. After being deeply buried, due to the isolation of air and sunlight, plastic is not easy to be weathered and decomposed, and more will cause groundwater pollution and hinder the infiltration of groundwater flow. Before landfilling, these wastes can be crushed into small fragments to accelerate their decomposition and weathering underground. Nowadays, the so-called environmental friendly plastic packaging also uses this principle to integrate some biodegradable materials into plastic materials to facilitate their decomposition underground

incineration

incineration method can incinerate the unusable mixed plastic paper in the incinerator, and the large amount of heat generated by it can be fully utilized again. After incineration, the volume of plastic can be reduced to less than 10% of the previous volume, and it is easy to decompose. However, it should be noted that a large number of harmful gases will be generated during the incineration process, which will cause harm to the environment and human body. Therefore, the treatment of waste gas and residues should meet certain standards

recycling

recycling is the most active way to promote the recycling of materials and the most effective treatment method to protect resources and the ecological environment

recycling can be recycled (reused)

this method is mainly aimed at large containers that are hard, smooth, clean and easy to clean, including large capacity liquid bottles, plastic barrels, etc

the process is roughly as follows:

split screening water washing sodium bisulfite soaking water washing distillation water washing

drying at 50 degrees corresponding to the hygiene inspection recycling

regeneration technology (secondary utilization)

mechanical treatment recycling: including direct recycling and modified recycling

the principle of direct recycling is simple, but the screening process is more complex. It is divided into closed and non closed. The so-called closure (for example, HDPE milk bottles are recycled and processed to be made back into cow milk bottles), that is, a large number of fresh similar resins are added during regeneration processing, about 90%. The products produced by this method are not significantly different from fresh resin products in use and mechanical operation characteristics, and have excellent regeneration performance

non closed (for example, HDPE milk bottles are recycled and made into HDPE detergent bottles for laundry, and then recycled and made into plastic boxes), that is, direct processing and cleaning, without or less use of fresh resin, and some additives are added in the mixing project to adjust the physical and chemical properties of the resin. Due to the aging of the material in the last use and in the reprocessing process, Therefore, the mechanical properties of this kind of recycled plastic products are lower than that of fresh resin

direct recycling and the sources and ways of waste plastics can be divided into three methods

1 There is no need to separate inspection, cleaning and other treatment. It is directly broken and plasticized. This method is used in the use of plastic packaging waste for some used but very clean plastic containers without any pollution

2. It should be treated by separation, cleaning, drying, crushing, etc. For containers without pollution, clean them to prevent damage to the instrument. The objects of this method are generally packaging waste collected from different channels after commodity circulation and consumption, packaging containers and films of various ways and shapes, etc

3. It needs special pretreatment. For example, PS plastic buffer materials should be treated with defoaming and volume reduction in advance, and then input into the machine for treatment

the purpose of modified recycling is to improve the basic mechanical properties of recycled materials to meet the quality needs of recycled special products. Modified regeneration is mainly divided into two categories, physical modification and chemical modification

physical modification with the help of mixing process, a certain amount of inorganic fillers should be added after the activation of plastic waste. At the same time, better surfactants should be added to increase the affinity between fillers and recycled plastic materials. However, in the processing process, the filler surface and resin surface are easy to form an interface layer, which has a great impact on the properties of recycled materials. The filler can be activated and then compounded

there is a big problem after the regeneration of waste plastics, that is, the mechanical properties are poor. The recycled materials can be toughened and modified at the same time of processing, that is, adding elastomers or blending thermoplastic elastomers to improve the toughness of the materials through blending. Reinforcement modification can also be used to enhance its mechanical properties. This kind of reinforcement often uses fibers to strengthen plastics. The properties of recycled materials will be greatly improved, and the strength and modulus will exceed the value of the original waste plastics. Its heat resistance, creep resistance and fatigue resistance are improved, but the brittleness of the product will increase, that is, its tensile breaking force will increase, and the fracture depth and length ratio will be greatly reduced

in the process of recovery and regeneration, several polymers can be mixed under the action of phase solvents to change their structure and intermolecular force and alloy them. This method can make recycled materials and many have excellent properties. The expected mechanical effect can be achieved by purposefully adding some characteristic main recycled materials in the processing process. If 25% LLDPE is blended with LDPE and blown into a film, the thickness will be reduced by 33% compared with the general film, and its tensile strength will increase by more than 45%, and the right angle tear strength will also increase by more than 50%. This can greatly extend the service life of agricultural film, reduce the amount of use and reduce the cost

the chemical modification of plastic packaging waste is to modify the material by means of chemical reaction to change its molecular structure, so as to obtain better special properties

there are many methods of chemical modification, but their essence is to play a chemical reaction on the old macromolecular chain or between chains, rely on the reactive groups at the molecular chain or the end of the chain to react again, connect a characteristic group to the chain, connect a characteristic branch chain, or in large part, the fund will obtain industry support for the reaction of the interchain reactive groups to form a bonding structure, which will lead to the change of material properties

there are two kinds of gluing modification: chemical gluing and radiation gluing. Chemical gluing usually makes the material fully plasticized above the softening point of the material, and then adds peroxide gluing agent to make the material molecules glued. Radiation bonding refers to the application of various high-energy rays of radiation sources to radiation bonding of materials with bonding agents

in reproduction application, physical and chemical modification can be carried out at the same time. Many equipment applying computer skills do not choose PC to be used on the same material. In a specific screw extruder, multiple materials are physically modified on one side for chemical modification, and then the two are blended. This technical method can not only shorten the time and production cycle of the improvement process, achieve continuous production, but also obtain better modification effect

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