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What Is Plastic?

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Author : Guangzhou Lefeng Plastic Bags Co.,Ltd
Update time : 2022-12-16 10:48:46
People get access to plastic like plastic bags almost every day, but what exactly is plastic?

Plastics are polymers whose main components are synthetic resins. In addition, according to the need to add additives with certain specific uses, such as plasticizer can improve plasticity, prevent plastic aging agent and so on.

Although the relative molecular weight of the polymer is very large, the composition is not complicated, and the structure has certain rules. They are made by the polymerization of small molecules, such as polyethylene, which is made by the polymerization of ethylene molecules.

When polyethylene plastic is heated to a certain temperature range, it begins to soften until it melts into a flowing liquid. When melted polyethylene plastic cools, it becomes a solid again, and when heated, it melts back into a liquid, a phenomenon called thermoplasticity. Polyethylene, polyvinyl chloride and polypropylene are all thermoplastics. Some plastics can only be softened when they are heated in the manufacturing process, and can be molded into a certain shape. After processing, they will not be reheated and melted, and have thermosetting properties, such as phenolic resin.

Why does this happen? This is because thermoplastics have a long, chain-like, linear structure. For example, the long chains of polyethylene and polyvinyl chloride are connected by C-C bonds, and these long chains are held together by intermolecular forces. When heated, these long chains vibrate more quickly, weakening the intermolecular forces between the chains and causing them to slide accordingly, so that the plastic melts into a liquid. As they cool, the longer chains hold less energy, draw closer together, and become more attractive to each other, so they reharden.

And thermosetting plastics at the beginning of the formation of long chains, heat will soften, can be molded into a certain shape. However, when thermosetting plastics are further heated, covalent bonds will be formed between chains, resulting in some cross-linking, forming a network structure and hardening. When they are reheated, the chain molecules are restricted from sliding and not melting.

There are many types of plastic and many different uses. For example, polyethylene, with good electrical insulation, chemical corrosion resistance, cold resistance and non-toxic, can be made into thin film, as packaging materials for food and medicine, as well as daily necessities, insulation materials, pipes and so on; Polyvinyl chloride has good electrical insulation, chemical corrosion resistance, organic solvent resistance, wear resistance, but poor thermal stability, poor air permeability, hardening when cold, it can be made into films, hoses, daily necessities, pipes, insulation materials, film can not be used to package food; Polypropylene has good mechanical strength, good electrical insulation, chemical corrosion resistance, light weight, non-toxic, but poor oil resistance, low temperature brittle, easy aging, it can be made into film, daily necessities, pipes, packaging materials, etc.

Polystyrene has good electrical insulation, good transmittance, chemical corrosion resistance, non-toxic, hard and brittle at room temperature, soft when the temperature is higher, poor oil resistance, it can be made into high frequency insulation materials, TV, radar parts, medical and health appliances, but also can be made into foam for shock proof, moisture proof, sound insulation, packaging pad material; Urea-formaldehyde plastic has good insulation, heat resistance, water resistance, easy coloring, can be made into electrical equipment, auto parts, daily necessities, etc. Polytetrafluoroethylene low temperature, high temperature, chemical corrosion resistance, solvent resistance, good electrical insulation, but the processing is difficult, it can be made into electrical, aviation, chemical, pharmaceutical, freezing and other industrial corrosion resistance, high temperature, low temperature products.

 
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