"Material knowledge" Five common plastics

Text "Material knowledge" Five common plastics

Plastic is a high molecular weight mixture polymerized by addition polymerization or polycondensation reaction with a monomer as a raw material, commonly known as plastic or resin, whose composition and shape can be freely changed. , lubricants, pigments and other additives. The main component of plastic is resin. Resin makes up 40% to 100% of total weight of plastic. The basic properties of plastics are mainly determined by nature of resin, but additives also play an important role. Some plastics are mainly composed of synthetic resins without additives or with a small amount of additives such as plexiglass, polystyrene, etc.

PE

Polyethylene is most productive grade in plastics industry. Polyethylene is a thermoplastic resin obtained by polymerization of ethylene. In industry, it also includes ethylene copolymers and a small amount of α-olefins. PE is odorless, non-toxic, feels like wax, has excellent low temperature resistance (the lowest operating temperature can reach -100~-70°C), good chemical stability, and can withstand most acids and alkalis (not oxidation resistant). ). ) nature of the acid). Insoluble in common solvents at room temperature, low water absorption, excellent electrical insulation. Polyethylene is commonly used in PE film, PE vest bags, PE food bags, baby bottles, buckets, kettles, etc.

"Material knowledge" Five common plastics

Polyethylene products

PP

Polypropylene is a thermoplastic resin obtained by polymerization of propylene. Polypropylene is a non-toxic, tasteless, odorless, highly crystalline milky polymer with a density of only 0.90-0.91 g/cm3, which is one of lightest types of all plastics. It is especially resistant to water with a water absorption rate of only 0.01% and a molecular weight of 80,000 to 150,000. Good moldability, but due to large shrinkage rate (1% ~ 2.5%), thick-walled products are easy to sag, and it is difficult to meet requirements for some parts with high dimensional accuracy and surface gloss of the product. good. Polypropylene is commonly used in microwave utensils, pots, plastic buckets, thermoses, woven bags, etc.

"Material knowledge" Five common plastics

Polypropylene products

PVC

PVC is a polymer formed by polymerization of vinyl chloride monomer in peroxide, azo compound and other initiators or by exposure to light and heat by free radical polymerization mechanism. PVC materials are often added with stabilizers, lubricants, auxiliary processing agents, dyes, impact agents, and other additives in actual use. Possesses incombustibility, high durability, resistance to climatic changes and excellent geometrical stability. Polyvinyl chloride is commonly used in plastic film, plastic shoes and leather goods, films, cables, and plastic bags.

Special attention: when PVC is made into soft plastics such as cling film and plastic bags, a large amount of auxiliary materials must be added, some of which are toxic, and harmful substances in this material can cause cancer after release.

"Material knowledge" Five common plastics

PVC products

PS

Polystyrene is a polymer synthesized by free radical addition polymerization of styrene monomer. It is a colorless and transparent thermoplastic with a glass transition temperature above 100°C, so it can often withstand boiling water temperatures, as well as disposable foam lunch boxes. In addition, polystyrene is also used in combs, boxes, ballpoint pen holders, children's toys, plastic shopping bags, etc.

Special attention: in production of disposable tableware, a large number of prohibited additives are used, such as heavy metals, which dissolve with water, vinegar, oil, etc. .

"Material knowledge" Five common plastics

PS Products

ABS

ABS is a copolymer of acrylonitrile, butadiene and styrene. ABS is a thermoplastic polymer material structure with high strength, good toughness and easy processing. ABS resin is a terpolymer of acrylonitrile, 1,3-butadiene and styrene. It can work normally at -25°C to 60°C and has good formability. The processed products have a smooth surface and are easy to paint and electroplate. And it can be mixed with various resins to form a mixture. ABS is mainly used in alloys, plastics and ABS grades.

"Material knowledge" Five common plastics

ABS plastic product

Source for this article: micro injection molding, mechanical engineer

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