PET can also be spun, that is, we often say polyester, so there is a saying that beverage bottles can be recycled for clothing during the Olympic Games. Many sportswear that pursue breathability and portability are made of polyester, and the popular material "polyester" is also made of it. However, due to the backward spinning method at that time, polyester clothes were not comfortable to wear now. In addition, PET has many engineering applications. ?
2.PE and polyethylene (high density polyethylene: HDPE；; Low density polyethylene: LDPE)? Main applications:? At present, PE is the most widely used plastic. Through different modification methods, PE can be applied to all aspects of daily life. Typical are plastic buckets, films, inner walls of paper cups, water pipes, cable sheaths, etc.
3.PVC, polyvinyl chloride? Main applications:? Pvc is now used to make some cheap artificial leather, foot pads, sewer pipes and so on. Because of its good electrical properties and certain flame retardant characteristics, it is widely used to manufacture wire and cable sheaths. In addition, PVC is also widely used in industrial fields, especially in places with high requirements for acid and alkali corrosion resistance. ?
4.PP, polypropylene? Main applications:? PP is also widely used, such as packaging, toys, washbasins, buckets, clothes hangers, cups, bottles and so on. Automobile bumper and other engineering applications. Polypropylene spun into silk is called polypropylene fiber, which is very common in textiles, non-woven fabrics, ropes, fishing nets and other products. ?
5.PS, polystyrene? Main applications:? Cheap transparent products, foam plastics, CD boxes, water cups, fast food boxes, thermal insulation lining, etc.
6.ABS, acrylonitrile-butadiene-styrene * * * polymer main uses:? ABS can be divided into many kinds according to the content of three components and the form of molecular chain, which is widely used in various electrical housings, office supplies components, safety helmets, doors and windows pipes, etc. ABS is commonly used in industry for * * * mixed modification of other plastics. ?
7.PA, polyamide? Main applications:? Mention another name of polyamide: nylon, you must be familiar with it. Polyamide family is very strong, whether it is PA6, PA66, PA 1 1 or PA 12, it has excellent physical and chemical properties. This is also the reason why PA is widely used in electronic appliances and automobile industries. In life, nylon rope and nylon stockings are also common items. The spun PA fiber is called nylon, which is used for fishing line, fishing net, rope and conveyor belt. ?
8.PC, polycarbonate? Main applications:? PC has excellent mechanical properties, toughness, rigidity and good light transmittance, and is often used in transparent cups, milk bottles, drinking buckets, CD substrates, lenses and lampshades.
9.*** mixture (XX-XX alloy)? Because a single plastic is difficult to meet the complex use requirements, different plastics are often mixed together to make plastic alloys in the plastic industry, which can not only give full play to the advantages of different materials, but also save the cost of developing new materials. ? Main applications:? Plastic alloys are widely used in various structural materials. For example, mobile phone cases are mostly PC-ABS alloy; In order to meet the needs of performance and processing, some sewer pipes use two kinds of PE alloys, which are called bimodal polyethylene.
Plastics are macromolecules polymerized from monomers through addition polymerization or polycondensation, commonly known as plastics or resins. The composition and shape can be changed freely, and it is composed of synthetic resin, fillers, plasticizers, stabilizers, lubricants, pigments and other additives.
The main component of plastic is resin. The word resin was originally named after the lipids secreted by animals and plants, such as rosin and shellac. Resin refers to a polymer compound without various additives. Resin accounts for about 40% ~ 100% of the total weight of plastics. The basic properties of plastics mainly depend on the properties of resin, but additives also play an important role. Some plastics are basically composed of synthetic resin with little or no additives, such as plexiglass and polystyrene.
The so-called plastic is actually a synthetic resin. Its shape is similar to turpentine in natural resin. It is artificially synthesized by chemical means, called plastic.
Plastics can be divided into thermosetting and thermoplastic, the former can not be used in plastic, and the latter can be produced repeatedly. The physical elongation of thermoplastics is relatively large, generally 50%~500%. Under different elongation, the force does not change completely linearly.
The different properties of plastics determine their industrial use. With the development of technology, the research on plastic modification has never stopped. It is hoped that in the near future, this modified plastic can be widely used, even replacing steel and other materials without polluting the environment.
There are basically two types: the first is linear structure, and the polymer compound with this structure is called linear polymer compound; The second is the bulk structure, and the polymer compound with this structure is called bulk polymer compound. Some polymers have branched chains, which are called branched polymers and belong to linear structure. Although some polymers are cross-linked between molecules, the degree of cross-linking is low, which is called network structure and belongs to bulk structure.
Two different structures show two opposite properties. Linear structure, melting by heating, less hardness and brittleness. The body structure is hard and brittle. There are two kinds of polymers in plastics, one is thermoplastic made of linear polymer, and the other is thermosetting plastic made of bulk polymer.
biodegradation
"The rapid biodegradation of plastics in Tenebrio molitor intestines reveals the new fate of plastic waste abandoned in the environment." Professor Yang Jun from Beihang University said.
Plastics are difficult to degrade naturally in the environment, and polystyrene is the most. Because of its high molecular weight and high stability, it is generally believed that microorganisms cannot degrade polystyrene plastics. 20 15 authoritative journals in the field of environmental science, such as Professor Yang Jun's research group of Beihang University and Dr. Zhao Jiao of Shenzhen Huada Gene Company &; Technology published two sister research papers, which proved that the larvae of Tenebrio molitor can degrade polystyrene, the most difficult plastic to degrade.
Studies show that Tenebrio molitor larvae can survive for more than 1 month with polystyrene foam as the sole food source, and eventually develop into adults, and the polystyrene they eat is completely degraded and mineralized into CO2 or assimilated into insect body fat. This discovery provides an idea for solving the global plastic pollution problem.
The plastic we usually use is not a single component, but is composed of many materials. Polymer (or synthetic resin) is the main component of plastic. In addition, in order to improve the properties of plastics, various auxiliary materials, such as fillers, plasticizers, lubricants, stabilizers, colorants, antistatic agents, etc. , must be added to polymer compounds to become a plastic with good performance.
Plastic additives, also known as plastic additives, are some compounds that must be added to improve the processability of polymers (synthetic resins) or the properties of resins themselves. For example, adding plasticizer to reduce the molding temperature of PVC resin and make the product soft; Another example is to add foaming agent to prepare lightweight, vibration-resistant, heat-insulating and sound-insulating foam plastics; The thermal decomposition temperature of some plastics is very close to the molding processing temperature, so it can't be molded without heating stabilizers. Therefore, plastic additives play a particularly important role in plastic molding.
When designing the mold, according to the shrinkage range of various plastics, the wall thickness and shape of the plastic parts, the size and distribution of the inlet, the shrinkage rate of each part of the plastic parts is determined according to experience, and then the cavity size is calculated. For high-precision plastic parts, it is difficult to master the shrinkage rate. Generally, the following methods should be adopted to design the mold:
(1) The external diameter of plastic parts shall be smaller and the internal diameter shall be larger, so that there is room for correction after die test.
(2) Try to determine the form, size and molding conditions of the gating system.
(3) The plastic parts to be post-treated should be post-treated to determine the dimensional change (measurement must be made 24 hours after demoulding).
④ Correct the mold according to the actual shrinkage.
⑤ Re-test the mold, appropriately change the process conditions, and slightly correct the shrinkage value to meet the requirements of plastic parts.