Термореактивті полимерлер: қасиеттері мен қолданылуы

Polymer obtained by irreversibly hardening (curing) a resin

In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure or mixing with a catalyst. Heat is not necessarily applied externally, and is often generated by the reaction of the resin with a curing agent (catalyst, hardener). Curing results in chemical reactions that create extensive cross linking between polymer chains to produce an infusible and insoluble polymer network. The starting material for making thermosets is usually malleable or liquid prior to curing, and is often designed to be molded into the final shape. It may also be used as an adhesive. Once hardened, a thermoset cannot be melted for reshaping, in contrast to thermoplastic polymers which are commonly produced and distributed in the form of pellets, and shaped into the final product form by melting, pressing, or injection molding.

Thermosetting plastics are generally stronger than thermoplastic materials due to the three dimensional network of bonds (crosslinking), and are also better suited to high temperature applications up to the decomposition temperature since they keep their shape as strong covalent bonds between polymer chains cannot be broken easily. The higher the crosslink density and aromatic content of a thermoset polymer, the higher the resistance to heat degradation and chemical attack. Mechanical strength and hardness also improve with crosslink density, although at the expense of brittleness. They normally decompose before melting. Hard, plastic thermosets may undergo permanent or plastic deformation under load. Elastomers, which are soft and springy or rubbery and can be deformed and revert to their original shape on loading release. Conventional thermoset plastics or elastomers cannot be melted and re shaped after they are cured. This usually prevents recycling for the same purpose, except as filler material. New developments involving thermoset epoxy resins which on controlled and contained heating form crosslinked networks permit repeatedly reshaping, like silica glass by reversible covalent bond exchange reactions on reheating above the glass transition temperature. There are also thermoset polyurethanes shown to have transient properties and which can thus be reprocessed or recycled.

When compounded with fibers, thermosetting resins form fiber reinforced polymer composites, which are used in the fabrication of factory finished structural composite OEM or replacement parts, and as site applied, cured and finished composite repair and protection materials. When used as the binder for aggregates and other solid fillers, they form particulate reinforced polymer composites, which are used for factory applied protective coating or component manufacture, and for site applied and cured construction, or maintenance purposes.