Glass Transition Temperature

property

The temperature range at which an amorphous polymer transitions from a rigid, glassy state to a flexible, rubbery state, marking a critical thermal property for processing and application performance.

In Simple Terms

Think of glass transition temperature as the point where a plastic changes from being stiff and brittle (like glass) to soft and flexible (like rubber). It's not a sharp melting point, but rather a temperature range where the polymer's molecular chains start moving more freely.

Why It Matters

Tg determines processing conditions, end-use temperature limits, and material selection. Resin traders use Tg data to match materials with applications, ensure proper storage conditions, and verify material quality during lot acceptance procedures.

Technical Details

Measured primarily by DSC analysis, Tg represents the temperature where polymer free volume increases rapidly, allowing segmental motion of molecular chains. For amorphous polymers like GPPS or PC, Tg defines the upper service temperature. Semi-crystalline materials exhibit Tg in their amorphous regions, affecting flexibility below melting point.

Real-World Examples

GPPS resin trading

General purpose polystyrene has a Tg around 100°C, making it suitable for disposable cups but limiting hot beverage applications above this temperature

Polycarbonate material selection

PC's high Tg of 150°C allows automotive interior parts to maintain rigidity in hot climates while remaining processable at molding temperatures

TPE compound verification

Certificate of analysis includes Tg measurements to ensure thermoplastic elastomers maintain flexibility at intended service temperatures