Classification of plastics

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The classification system for plastics is quite complex, and various classification methods overlap with one another. The main classification methods, according to conventional practices, are as follows: the first is classification based on usage characteristics； The second is classification by physicochemical properties ； Third is classification by processing method. 1. Classification by application characteristics: Based on the different application characteristics of various plastics, they are generally divided into three categories: general-purpose plastics, engineering plastics, and specialty plastics. (1) General-purpose plastics generally refer to plastics that are produced in large quantities, have a wide range of applications, good formability, and low costs, such as polyethylene, polypropylene, and phenol-formaldehyde resins. (2) Engineering plastics generally refer to plastics that can withstand certain external forces, possess good mechanical properties as well as resistance to high and low temperatures, and have good dimensional stability; they can be used in engineering structures, such as polyamides and polysulfones. Among engineering plastics, they are further divided into two main categories: general-purpose engineering plastics and special engineering plastics. Common engineering plastics include: polyamides, polyoxymethylenes, polycarbonates, modified polyphenylene ethers, thermoplastic polyesters, ultra-high molecular weight polyethylene, methylpentene polymers, vinyl alcohol copolymers, and others. Special engineering plastics are further divided into cross-linked and non-cross-linked types. Cross-linked types include polyamino-bismaleimide, polytriazine, cross-linked polyimide, and heat-resistant epoxy resins. Non-crosslinked types include: polysulfone, polyethersulfone, polyphenylene sulfide, polyimide, polyether ether ketone (PEEK), etc. (3) Specialty plastics generally refer to plastics with special functions that can be used in specialized fields such as aviation and aerospace. Plastics such as fluoroplastics and silicones possess outstanding special properties like high temperature resistance and self-lubrication, while reinforced plastics and foam plastics have special characteristics such as high strength and high cushioning capacity; all of these plastics fall under the category of specialty plastics. •　Reinforced plastic. In terms of shape, reinforced plastic raw materials can be divided into three types: granular (such as calcium-plastic reinforced plastics), fibrous (such as glass fiber or glass cloth reinforced plastics), and flaky (such as mica reinforced plastics). Based on the material, they can be divided into three types: fabric-reinforced plastics (such as those reinforced with chopped fabric or asbestos), inorganic mineral-filled plastics (such as those filled with quartz or mica), and fiber-reinforced plastics (such as carbon fiber-reinforced plastics). •　Foam plastic. Foam plastics can be divided into three types: rigid, semi-rigid, and soft foam plastics. Rigid foam plastics lack flexibility and have a high compressive stiffness; they only deform when a certain stress level is reached, and they cannot return to their original shape once the stress is removed ； Soft foam plastics are highly flexible, have very low compressive stiffness, can be easily deformed, and return to their original shape once the stress is removed, with minimal residual deformation ； The flexibility and other properties of semi-rigid foam plastics lie between those of rigid and soft foam plastics. 2. Classification by physical and chemical properties: Based on the various physical and chemical properties of different plastics, they can be divided into two types: thermosetting plastics and thermoplastic plastics. (1) Thermosetting plastics: Thermosetting plastics are those that can be cured under heat or other conditions, or that possess insoluble (non-melting) properties, such as phenolic plastics and epoxy plastics. Thermosetting plastics are further divided into formaldehyde-crosslinked types and other crosslinked types. Formaldehyde-crosslinked plastics include phenolic plastics and amino plastics (such as urea-formaldehyde-melamine-formaldehyde, etc.). Other cross-linked plastics include unsaturated polyesters, epoxy resins, phthalaldehyde diallyl resin, and others. (2) Thermoplastic plastics: Thermoplastic plastics are those that can be repeatedly heated to soften and cooled to harden within a specific temperature range, such as polyethylene and polytetrafluoroethylene. Thermoplastic plastics are further divided into various types such as hydrocarbons, vinyl-based plastics containing polar groups, engineering plastics, and cellulose-based plastics. •　Hydrocarbon plastics. They belong to non-polar plastics and can be divided into crystalline and amorphous types. Crystalline hydrocarbon plastics include polyethylene, polypropylene, etc., while amorphous hydrocarbon plastics include polystyrene, etc. •　Vinyl plastics containing polar genes. With the exception of fluoroplastic materials, most are amorphous transparent substances, including polyvinyl chloride, polytetrafluoroethylene, polyvinyl acetate, and others. Most vinyl monomers can be polymerized using free-radical catalysts. •　Thermoplastic engineering plastics. These mainly include polyoxymethylene, polyamides, polycarbonates, ABS, polyphenylene ethers, polyethylene terephthalate, polysulfones, polyethersulfones, polyimides, and polyphenylene sulfides. Polytetrafluoroethylene. Modified polypropylene and the like are also included in this category. #8226; Thermoplastic cellulose plastics. They mainly include cellulose acetate, cellulose acetate butyrate, celloidine, cellophane, etc. 3. Classification of processing methods: Based on the different molding methods for various plastics, they can be divided into various types such as film pressing, laminating, injection molding, extrusion, blow molding, casting plastics, and reactive injection molding. Membrane-pressure plastics are mostly plastics whose processing properties are similar to those of ordinary solid plastics ； Laminated plastic refers to a material formed by combining fiber fabrics impregnated with resin through layering and heat pressing ； Injection molding, extrusion, and blow molding are mostly used for plastics whose physical properties and processing characteristics are similar to those of ordinary thermoplastics ； Cast plastic refers to a liquid resin mixture that can be poured into molds under zero pressure or slight pressure and hardened into products of specific shapes, such as MC nylon ； Reactive injection molding is a type of plastic manufacturing process in which liquid raw materials are injected under pressure into a mold cavity, where they react and solidify to form products of specific shapes, such as polyurethanes.