Meaning
Thermal liberation of diol monomer fragments during high-temperature polyester processing marks the breakdown of polymer backbone chains under heat and moisture. Excess release of these volatile compounds, termed ethylene glycol evolution, indicates chain scission and intrinsic viscosity reduction inside injection moulding barrels. The boundary of this reaction covers thermal processing temperatures above two hundred degrees Celsius where ester bonds cleave, releasing free glycol into processing vents and dryer exhaust streams.
Polymer Degradation
Melt processing of polyethylene terephthalate requires rigorous drying to prevent hydrolytic degradation during plastication. When moisture levels exceed fifty parts per million, accelerated ethylene glycol evolution occurs, severing ester linkages and dropping molecular weight. Lower intrinsic viscosity reduces melt strength, causing parison sag in blow moulding operations and structural failure in thin-walled containers.
Volatile Emission
Exhaust gas analysis monitors diol gas concentrations escaping from melt degassers and vacuum vents on extrusion lines. Uncontrolled ethylene glycol evolution deposits sticky condensates inside vacuum lines, clogging filtration units and causing process downtime. Continuous vacuum extraction removes liberated diols before they re-enter the polymer melt.
Process Control
Processing temperature management limits thermal scission in high-heat moulding zones. Excessive heat input triggers rapid ethylene glycol evolution, generating acetaldehyde byproducts that alter product clarity and taint food-contact packaging.
