Thermoplastics can be further divided into three categories: general-purpose plastics, general-purpose engineering plastics, and high-performance engineering plastics.
1. Good elasticity and compression deformation resistance, environmental resistance and aging resistance are equivalent to EPDM rubber, and its oil resistance and solvent resistance are comparable to general-purpose neoprene rubber.
2. Wide application temperature range (-60~150℃), wide application range of softness and hardness (25A~54D), and the advantage of easy dyeing greatly improves the freedom of product design.
3. Excellent processing performance: It can be processed by injection, extrusion and other thermoplastic processing methods, which is efficient, simple and easy, without additional equipment, high fluidity and small shrinkage.
4. Green and environmental protection, recyclable, and repeated use for six times without significant performance degradation, in line with EU environmental protection requirements.
5. Light specific gravity (0.90~0.97), uniform appearance quality, high surface grade and good hand feeling.
It becomes soft and fluid when heated, and hardens when cooled. This process is reversible and can be repeated. Such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic plastics, other polyolefins and their copolymers, polysulfone, polyphenylene ether, chlorinated polyether, etc. are thermoplastics.
The resin molecular chains in thermoplastics are all linear or branched structures. There is no chemical bond between the molecular chains. It softens and flows when heated, and the process of cooling and hardening is a physical change.
2. Thermosetting plastics
When it is heated for the first time, it can soften and flow. When it is heated to a certain temperature, a chemical reaction occurs to cross-link and solidify to harden. This change is irreversible. After that, when it is heated again, it can no longer become soft and flow.
It is by virtue of this characteristic that the molding process is carried out, and the plasticized flow during the first heating is used to fill the cavity under pressure, and then solidify into a product of a determined shape and size. This material is called a thermoset.
The resin of thermosetting plastics is linear or branched before curing. After curing, chemical bonds are formed between molecular chains to form a three-dimensional network structure. Not only can it not be melted again, but it cannot be dissolved in solvents. Phenolic, urea-formaldehyde, melamine-formaldehyde, epoxy, unsaturated polyester, silicone and other plastics are all thermosetting plastics.
It is mainly used for heat insulation, wear resistance, insulation, high voltage resistance and other plastics used in harsh environments. Most of them are thermosetting plastics. The most commonly used ones should be wok handles and high and low voltage electrical appliances.