Classification and difference of plastics
(一) Classified according to performance and use Plastics can be classified into general plastics and engineering plastics according to performance and use. General plastic refers to general-purpose plastics. It has a wide range of uses, large output, and low prices. It is a plastic that is used in buildings. Engineering plastics refers to polymers with higher mechanical strength and other special properties.
(二) According to the classification of thermal properties of plastics Plastics can be divided into thermoplastic and thermosetting plastics according to different thermal properties. The changes that occur when they are heated are different, and their heat resistance, strength, and stiffness are also different.
The thermoplastic softens or melts when it is heated, and hardens and sets after cooling. No chemical changes occur in the cold or hot process. This performance is maintained regardless of how many times the heating and cooling are repeated. Therefore, the forming process is simpler and has higher mechanical properties. , but the heat resistance and rigidity are poor. The resins in thermoplastics are all linear molecular structures, including all polymeric resins and partial condensation resins. Typical varieties are polyethylene, polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, ABS plastic, poly. Amide, polyoxymethylene, polycarbonate, polyphenylene oxide, etc.
During the processing of thermosetting plastics, they are softened by heat, then solidified, hardened, and cannot be softened. Chemical changes occur during processing. Adjacent molecules crosslink to form a bulk structure and harden into infusible and insoluble materials. Heat resistance and stiffness are good, but mechanical strength is low. Most of the plastics produced from condensation resins are thermosetting, and plastics such as phenolics, epoxies, amino resins, unsaturated polyesters, and polysilicone resins are among these.
