Thermal Transitions: Tg, Tc, Tm
topic
PET thermal transitions by DSC: glass transition Tg ~67°C (amorphous PET), 80–90°C (oriented/crystalline); cold crystallisation exotherm Tc ~130°C (amorphous PET heated above Tg); melting endotherm Tm ~255°C (decreases with comonomer, lower crystallinity). Double melting peaks indicate recrystallisation during heating. Tg depressed by plasticisers, moisture, and low MW.
Role
Understanding PET thermal transitions is essential for designing processing conditions (drawing above Tg, heat-setting below Tm), predicting fabric dimensional stability in laundering and ironing, and interpreting DSC thermograms in fibre analysis.
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