Thermal and Thermooxidative Degradation
topic
PET undergoes thermal degradation above 290°C via β-scission (chain scission generating vinyl ester and carboxyl ends), ester exchange (random transesterification reducing MW), and oxidative degradation (in presence of O₂, generating chromophores causing yellowing). Acetaldehyde (AA) is a major volatile by-product. Thermal degradation increases IV loss and DEG content.
Role
Controlling thermal degradation during melt spinning is essential for maintaining fibre quality, colour, and IV. It governs processing temperature windows and residence time limits in the extruder and spin pack.