Thermosetting Plastics

Synthetic polymers can be divided into two broad groups according to their behaviour when exposed to heat and pressure. All polymers soften and flow (ie become plastic) under such conditions. One group undergoes only the physical change of softening, and on cooling resumes a solid state. This process of softening and solidifying can be performed repeatedly and the materials in this group are known as thermoplastic polymers. Materials in the second group soften on heating, but in addition undergo an irreversible chemical reaction and ultimately solidify into a form which cannot again be softened by heating. These materials are known as thermosetting polymers.