Thermoplastic
A
thermoplastic, also called a
thermosoftening plastic is a polymer which becomes pliable or moldable above a specific temperature and returns to a solid state upon cooling. Most thermoplastics have a high molecular weight. The polymolecules chains associate through intermolecular forces, which permits thermoplastics to be remolded because the intermolecular interactions increase upon cooling and restore the bulk properties. In this way, thermoplastics differ from thermosetting polymers, which form irreversible chemical bonds during the curing process. Thermosets often do not melt, but break down and do not reform upon cooling. Stress strain graph of thermoplastic material. Above its glass transition temperature,
Tg, and below its melting point,
Tm, the physical properties of a thermoplastic change drastically without an associated phase change. Within this temperature range, most thermoplastics are rubbery due to alternating rigid crystalline and elastic amorphous regions, approximating random coils. Some thermoplastics do not fully crystallize above glass transition temperature
Tg, retaining some, or all of their amorphous characteristics.