Tg explained.
Plastic stiffness.
Material behavior.
Glass transition temperature (Tg) reference. Plastic stiffness changes at Tg. Below: rigid. Above: flexible. Critical for service temperature.
Key principles.
Stiffness change
Temperature where amorphous plastic transitions stiff to flexible.
Rigid
Below Tg, plastic glassy and rigid. Standard service.
Rubbery
Above Tg, plastic rubbery. Generally avoid.
Tm matters more
Crystalline plastics melting point (Tm) more relevant.
Various Tg
PC 150°C. ABS 105°C. Nylon 50-60°C. PEEK 143°C.
Below Tg
Service temperature below Tg. Safety margin 20-30°C.
FAQ
Why does Tg matter?
Plastic loses stiffness above Tg. Service must stay below for structural applications.
Tg vs melting point?
Tg: amorphous transition (gradual). Tm: crystalline melting (sharp). Different mechanisms.
Common plastic Tgs?
PC 150°C. ABS 105°C. Nylon (PA66) 60°C. PEEK 143°C. PVC 80°C. PS 100°C.
Service temperature?
Continuous service ≤ Tg minus 20-30°C safety margin. Structural applications.
Glass-filled effects?
Glass fiber raises effective service temperature, less Tg dependent.
Specifying for design?
Specify continuous service temperature. Material/process select per Tg.
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