Pre-Spinning Drying and Moisture Control
topic
PET must be dried to <50 ppm moisture (preferably <30 ppm) before melt spinning to prevent hydrolytic degradation causing IV loss and chain scission. Drying uses dehumidified hopper dryers (dew point ≤ −40°C) at 160–180°C for 4–6 hours. Crystallisation at 160°C precedes drying to prevent chip agglomeration. Moisture content measured by Karl Fischer titration.
Role
Inadequate drying is the most common cause of IV drop, gel formation, and filament breakage in polyester spinning. Moisture control is a critical first process control point determining downstream fibre quality.