There are many kinds of plastics, including dozens of main ones. Plastics are classified in the following ways:
（1） Classification by application scope
1. General plastic
General purpose plastics refer to a kind of commonly used plastics with large output, wide uses, low cost and various properties. Polyvinyl chloride, polyethylene, polypropylene, polystyrene and phenolic plastics are the five general plastics. Other polyolefins, vinyl plastics, acrylic plastics and amino plastics also belong to general plastics. Their output accounts for more than half of the total plastic output and constitutes the main body of the plastic industry.
2. Engineering plastics
Engineering plastics refer to a kind of plastics with excellent performance and can be used as engineering materials or structural materials. For example, polyamide, polyformaldehyde, polycarbonate, polysulfone and acrylonitrile butadiene styrene copolymer (ABS copolymer or ABS) are engineering plastics with excellent mechanical properties or heat resistance, corrosion resistance and wear resistance.
3. Special plastics
Special plastics, also known as functional plastics, refer to plastics with certain special functions. For example, it is used for conductive, magnetic, photosensitive, anti radiation, optical fiber, liquid crystal, polymer separation membrane and other plastics. Special plastics are generally obtained by special treatment or modification of resins for general plastics or engineering plastics, but some are made of special resins specially synthesized.
（2） Classification by heating property
1. Thermoplastic
Thermoplastics soften when heated, and even become viscous substances with certain fluidity. At this time, it has plasticity, which can be made into products with a certain shape, which can be hardened and shaped after cooling; If it is reheated, it becomes soft again, and can be processed into products of another shape. After cooling, it will harden and set. This can be repeated many times. Plastics with this property are called thermoplastics. Polyvinyl chloride, polypropylene, polystyrene, polymethylmethacrylate, polyformaldehyde, polyamide and polycarbonate are all thermoplastics.
Thermoplastics are developing rapidly. In recent years, a number of thermoplastics with special properties have been developed, such as polysulfone, fluoroplastics and so on.
2. Thermosetting plastics
During processing, thermosetting plastics will also change at first and have certain plasticity. They can be made into parts with certain shape. However, after continuous heating or adding curing agent, they will harden (cure) with the occurrence of chemical reaction, so that the shape will be fixed and will not change (set). The cured plastic is hard and insoluble in solvent. If it is reheated, it will not soften and has no plasticity. If the temperature is too high, it will decompose. Plastics with this property are called thermosetting plastics. Phenolic plastics (bakelite), urea formaldehyde plastics (Dianyu), epoxy resin and unsaturated polyester are thermosetting plastics.
（3） Classification according to the synthetic route of raw resin
1. Plastics based on polymerized resin
The addition polymerization resin is the synthetic resin obtained by the addition polymerization reaction. Common are polyvinyl chloride, polyolefin, polystyrene, polymethylmethacrylate, polytetrafluoroethylene, etc.
2. Plastics based on polycondensation resin
Phenolic resin is common.
3. Plastics with natural polymer compounds as raw materials
Based on natural polymer compounds, plastics must be made through chemical processing. Nitrocellulose and cellulose acetate are common.