There are two different types of Plastics: Thermoplastics and thermosetting plastics. Hot melt plastics become soft and flow when heated, and harden when cooled. This process is reversible and can be repeated. Polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyformaldehyde, polycarbonate, polyamide, acrylic plastics, other polyolefins and their copolymers, polysulfone, polyphenylene ether, chlorinated polyether, etc. are thermoplastics. In thermoplastics, the resin molecular chains are linear or branched, and there is no chemical bond between the molecular chains. The process of softening and flowing when heated and hardening when cooled is a physical process of morphological transformation. Thermosetting plastics can soften and flow when heated to a certain temperature, produce chemical reaction, cross chain curing and harden. This change is irreversible. After that, when heated again, they can no longer soften and flow. This material is called thermosetting plastics.

對于熱固性聚合物的這種交聯(lián)反應(yīng)，粘度反映了它的固化程度。借助這種特性可以對熱固性塑料進(jìn)行成型加工，一次加熱時的塑化流動，在壓力下充滿型腔，進(jìn)而固化成為確定形狀和尺寸的制品。熱固性聚合物在成型中不僅有物理狀態(tài)的變化，還有化學(xué)變化，并且是不可逆的。

For this crosslinking reaction of thermosetting polymer, the viscosity reflects its curing degree. With this feature, thermosetting plastics can be shaped and processed. The plasticizing flow during one-time heating will fill the mold cavity under pressure, and then solidify into products with certain shape and size. Thermosetting polymers have not only physical state changes, but also chemical changes, and are irreversible.

熱固性聚合物在未交聯(lián)前與熱塑性聚合物相似，都是線型聚合物。但熱固性聚合物在分子鏈中帶有反應(yīng)基團(tuán)或反應(yīng)活點，成型時分子鏈通過自帶的反應(yīng)基團(tuán)的作用或反應(yīng)活點與交聯(lián)劑（硬化劑）的作用而發(fā)生交聯(lián)，使線型變成體型結(jié)構(gòu)，不僅不能再熔觸，在溶劑中也不能溶解。

Thermosetting polymers are similar to thermoplastic polymers before crosslinking. They are linear polymers. However, thermosetting polymers have reaction groups or reaction active points in the molecular chain. During molding, the molecular chain is crosslinked through the action of its own reaction groups or reaction active points and crosslinking agents (hardeners), so that the linear structure becomes a body structure, which can not be fused and dissolved in the solvent.

酚醛、服醛、三聚氰胺甲醛、環(huán)氧、不飽和聚酯、有機(jī)硅等塑料都是熱固性塑料。熱固性塑料可以用作隔熱、耐磨、絕緣、耐高壓電材料，如炒鍋鍋把手和高低壓電器。

Phenolic, formaldehyde, melamine formaldehyde, epoxy, unsaturated polyester, silicone and other plastics are thermosetting plastics. Thermosetting plastics can be used as heat insulation, wear resistance, insulation and high-voltage electrical materials, such as frying pan handles and high-voltage and low-voltage electrical appliances.

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