Glastillståndstemperatur

Glastillståndstemperatur, often abbreviated as Tg, refers to the temperature range at which an amorphous solid transitions from a hard, brittle state to a more pliable, rubbery state. This phenomenon is characteristic of glassy polymers, but it can also be observed in other amorphous materials like some ceramics and metals. Unlike a true melting point, which is a sharp, defined temperature for crystalline solids, the glass transition is a gradual process that occurs over a range of temperatures.

Below the glastillståndstemperatur, polymer chains have very limited mobility. The material behaves like a rigid, glassy solid. As the temperature increases and reaches the glass transition range, kinetic energy is imparted to the polymer segments. This allows for increased segmental motion and rotation, leading to a significant decrease in the material's stiffness and a corresponding increase in its ductility and impact resistance. Above the glass transition temperature, the polymer is considered to be in a rubbery state.

The glastillståndstemperatur is an important parameter in material science and engineering as it dictates the service temperature and mechanical properties of many polymeric materials. For example, a plastic used in outdoor applications needs to have a Tg significantly below the expected ambient temperature to maintain its structural integrity and prevent embrittlement in cold conditions, while a material intended for high-temperature use would require a higher Tg. Factors such as molecular weight, cross-linking, and the presence of plasticizers can influence the Tg of a polymer.