Cooling thermosetting resins

Plastics are subidivided into two types thermoplastic and thermosetting. The thermoplastics can be softened by heat and hardened again by subsequent cooling. This process is reversible and can be repeated many times. By contrast, the thermosetting resins are first softened and melted and, at subsequent heating to a definite temperature, they are irreversibly hardened, becoming insoluble [53]. 

Common to all reinforced plastics are two ingredients, resin and reinforcement. Resin is an oiganic material, usually of high molecular weight, that can be molded and set into a final shape. Resins are of two basic types. Thermoplastic resins soften upon heating, are shaped in a mold, and retain that shape when cooled. Common examples are nylon, polyethylene, polypropylene, and polycarbonate. Thermosetting resins are placed in a mold and cured by the use of a catalyst, heat, or both, until they harden in the shape of the mold. Common examples are polyester, vinyl ester, epoxies, phenolics, and p olyure thanes. 

Unlike the thermosetting resins, the thermoplastic resins will soften on heating or on contact with solvents. They will then harden on cooling or on evaporation of the solvent from the material. This is a result of the noncrosslinked chemical structure of thermoplastic molecules. The following are important characteristics of thermoplastic resins that can affect their joining capability. 

Thermosetting Resin Any hydrocarbon polymer that hardens when cooled after being heated for plasticity. 

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