Warm Global Customers
With China Plastic Machinery
With China Plastic Machinery
Thermosetting polymers generally form prepolymers first, and when they are molded, they are heated so that the potential functional groups therein continue to react into a cross-linked structure and solidify.
The transformation of thermosetting polymers is irreversible and can only be molded once. They cannot melt and plasticize when heated again, and they are also insoluble in solvents. They are generally three-dimensional polymers, such as phenolic resins, vulcanized rubber, etc.
Thermosetting polymers refer to polymers that become three-dimensional structures through chemical cross-linking between molecules. The cross-linking reaction is irreversible, so its processing characteristic is that it can only be molded once and cannot be processed again in the same way. Thermosetting polymers are insoluble and infusible because of the stable chemical cross-linking. The preparation of thermosetting polymers can be directly synthesized from monomers or using prepolymers.
Prepolymers can be divided into two categories. One is the co-condensation of bifunctional and trifunctional monomers. For ease of processing, the reaction is usually terminated before gelation and formulated into molding materials. During the final molding, one side flows to fill the mold cavity, and the other side is heated and cross-linked into products, such as polyesters generated by the reaction of phthalic anhydride and glycerol, alkali-cured phenolic resins and urea-formaldehyde resins.
The first category is the product of polycondensation between bifunctional monomers. It must be further cross-linked under the action of a catalyst or a cross-linking agent, such as epoxy resins, unsaturated polyesters, linear phenolic resins, various polyether or polyester plastics, etc. Due to the high cross-linking density of thermosetting polymers, the movement and crystallization of chain segments are restricted, resulting in a very high or non-existent T. Generally, it has high hardness, high heat resistance, good dimensional stability, and can be used as structural materials, civilian products, daily necessities and certain engineering materials.
It can soften and flow when heated for the first time. When heated to a certain temperature, a chemical reaction occurs, cross-linking and curing occurs, and it becomes hard. This change is irreversible. After that, it can no longer soften and flow when heated again. It is precisely with the help of this characteristic that molding is carried out. The plasticized flow during the first heating is used to fill the mold cavity under pressure, and then solidify into a product of a certain shape and size. This material is called a thermosetting plastic.
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