Extrusion & Post
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EVOH extrusion melt fracture
Problem Phenomenon
EVOH shows severe melt fracture at excessive extrusion rate, extrudate twisted in a spiral shape
Cause Analysis
EVOH melt elasticity too high, elastic recovery at the die exit exceeding the critical value; die L/D ratio too short <10 with melt not fully relaxed; extrusion temperature too low
Solution
1) Reduce extrusion rate to 2-3m/min; 2) Increase die L/D ratio to 15-20; 3) Increase extrusion temperature to 190-230°C; 4) Add a small amount of low-elasticity resin to reduce system elasticity; 5) Gradual contraction die inlet design
Key Takeaway
Melt fracture is caused by elastic recovery exceeding the critical value; reducing speed and lengthening the die are core countermeasures
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