Processing, thermosets terms Links

Unlike thermoplastics, which are simply melted, thermoset resins chemically react from low-viscosity liquids to solid materials during processing, a process termed curing. Structurally, thermosets differ from thermoplastics because of the presence of cross-links in the former, which means that thermosets cannot be reshaped or recycled once the chemical reaction occurs. One advantage of thermosets vs. thermoplastics is that wetting the filler becomes much easier with a low-viscosity material. By far the most common thermoset composite is automobile tires, which consist of a polymer made from styrene and butadiene monomers and carbon-black filler. The actual recipe used is much more complicated, and can include other monomers or polymers, as well as other fillers. In the absence of filler, the cured resin is rubbery at room temperature, which makes tires a... 

If we return to our structural classifications and isolate the two ends of the spectrum— linear and highly cross-linked polymers—we find that we can establish still another method of classification based on processibility. Linear polymers can be melted or thermally softened and as such can be termed thermoplastic. On the other hand, the highly cross-linked material cannot be melted or appreciably softened. In fact, such a polymer will thermally decompose or bum before it melts. The highly cross-linked polymers are classified as thermosetting polymers, or thermosets. One further distinction between thermoplastics and thermosets is that the former are generally somewhat soluble whereas the latter are insoluble. Table 1-1 summarizes the two classes. 

The layman s term for the time/lemperature related molecular cross-linking process - known more correctly as polymerisation - which occurs when a thermoset resin changes from the typically viscous liquid to the solid state. This cure process is normally also promoted following chemical activation by a catalyst - or often called, hardener -addition. Other chemical accelerators may be added by the resin manufacturer, or alternatively added to the resin immediately prior to the catalyst addition. Cure can also be activated in other ways, such as by the influence of ultra-violet radiation. No by-products are formed during the formation of these long molecular cross-linked chain links. 

---