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Classification of Plastics

Classification of Plastics

According to the molecular structure and thermal characteristics of plastic synthetic resin, it can be divided into thermoplastic and thermosetting plastics. This classification method reflects the structure, physical properties, chemical properties and molding properties of the polymers.

Thermoplastic: when heated at a certain temperature range, it softens and melts to become a flowing viscous liquid, which can be formed into products of a certain shape. After cooling, it hardens to maintain the formed shape, and the process can be repeated. This kind of plastic has only physical change but no chemical change in the molding process, and its resin molecular chain is linear or with branched chain structure, there is no chemical bond between the molecular chain. Common thermoplastics are polyethylene, polypropylene, polystyrene, polyvinyl chloride, polymethylpropionate methyl ester (plexiglass), acrylonitrile - butadiene - styrene (ABS), polyamide (nylon), polyformaldehyde, polycarbonate, polyphenyl ether, polysulfone and polytetrafluoroethylene.

Thermosetting plastics: the first time when the heat can soften the flow, heating to a certain temperature, chemical reaction, cross chain solidification and become hard, at this time the resin becomes not melting and hardening, plastic parts shape is fixed no longer change. It is with this characteristic that the molding process is carried out, and the plasticizing flow during the first heating is utilized to fill the shape cavity under pressure, and then solidify into the products with definite shape and size. Thermosetting plastic resin before curing is linear or with a branch chain, after curing the formation of chemical bonds between the molecular chain, into a three-dimensional network structure, not only can not melt, in the solvent can not be dissolved, that is, curing. This process involves both physical and chemical changes, and unlike thermoplastics, these products cannot be recycled once they are damaged. Phenolic plastics, amino plastics, epoxy plastics, silicone plastics, unsaturated polyester plastics are commonly used thermosetting plastics.

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