How does an increase in glass transition temperature (Tg) affect the thermal stability and processing conditions of a polymer during manufacturing?

When a polymer’s glass transition temperature rises, the material stays in a hard, glassy state up to a higher temperature, so it can withstand more heat before becoming soft or deforming. This higher Tg improves the polymer’s thermal stability during use, but it also means that during manufacturing the material must be heated to a higher temperature to reach the melt or flow regime. As a result, extrusion, injection molding or other processing steps need stronger heating elements, longer dwell times, or higher pressure to compensate for the increased viscosity. For example, polycarbonate has a Tg of about 150 °C, so it is processed at temperatures above 200 °C, whereas PET with a Tg of roughly 70 °C can be molded at lower temperatures. Thus, a higher Tg polymer requires more energy and careful temperature control to avoid overheating while still achieving proper flow.