Thermosetting plastics can soften and flow when they are first heated to a certain temperature, resulting in a chemical reaction, cross-linking reaction and hardening. This change is irreversible. Thereafter, when they are heated again, they can no longer soften and flow. It is precisely with this characteristic that the moulding process is carried out, and the moulding flow during the first heating is utilized to fill the cavity under pressure, and then solidify into a product with definite shape and size.
Thermosetting plastics are characterized by chemical reaction and hardening at a certain temperature after heating, pressurizing or adding hardener for a certain time. After hardening, the chemical structure of the plastics changes, the texture is hard, insoluble in solvents, and no longer softens when heated. If the temperature is too high, the plastics will decompose. Resin molecular chains in thermoplastics are linear or branched structures. There are no chemical bonds between the molecular chains, which soften and flow when heated. The process of cooling and hardening is a physical change.
Formaldehyde crosslinking plastics include phenolic plastics and amino plastics (such as urea-formaldehyde-melamine-formaldehyde, etc.). Other cross-linking plastics include unsaturated polyester, epoxy resin, o-phthalenediallyl ester resin and so on.
The commonly used thermosetting plastics are phenolic resin, urea-formaldehyde resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, polyurethane and so on.
How does the Clothes plastic labeling (plastic clothing tag) made?
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