According to the molecular structure and thermal properties of synthetic resin in plastics, there are four kinds of plastics, one is thermoplastic and the other is thermosetting. [1] Characteristics of thermoplastics 1) The molecules of the resin are linear or chain-shaped. 2) Softening when heating, melting when reaching a certain humidity, becoming a flowable viscous silo, which can be molded into a certain shape under a certain pressure, and can keep the molded shape after cooling. If heated again, it can be softened, melted and molded repeatedly. 3) In the process of heating and cooling, there are only physical changes and no chemical changes. (2) Characteristics of thermosetting plastics. The molecular structure of 1) resin. 2) At the beginning of heating, the molecules in the shade are still linear in structure and still have the plasticity of thermoplastic. When heating is continued, the main chain of linear molecules breaks into chemical chains (i.e. cross-linking). Molecules have a network structure. When the temperature reaches a certain value, the molecules become a bulk structure, and the tree crispness becomes an insoluble shape. Repeated heating will not soften or be plastic. 3) There are both physical and chemical changes in the formation process. Thermoplastics mainly include polyethylene, polyvinyl chloride, ABS, polypropylene polystyrene, nylon, formaldehyde and so on. Tools: complete cookbooks, Chinese dictionary, Chinese dictionary, complete idioms, complete allegorical sayings, complete riddles and free naming.