Material Drying
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PEI Insufficient Drying Bubbles and Silver Streaks
Problem Phenomenon
Bubbles, silver streaks, surface pitting, and delamination appear on the surface of PEI products; defects are obvious on transparent amber parts, and mechanical properties decline simultaneously.
Cause Analysis
PEI molecules contain ether bonds and imide groups and are extremely hygroscopic, with an equilibrium water absorption of about 0.5%; moisture content exceeding 0.02% causes appearance problems, brittle parts, and abnormal melt flow; at high temperatures, moisture vaporizes and triggers degradation.
Solution
①Dehumidifying dryer at 150℃×4 hours (6 hours for reinforced grades), dew point -29~-40℃; ②verify moisture content ≤0.02%; ③store in a sealed hopper after drying; if exposed to air for more than 10 minutes, re-drying is required; ④when silver streaks appear, verify drying first.
Key Takeaway
PEI's 0.02% moisture content red line is stricter than most engineering plastics; a dehumidifying dryer is an essential configuration; the 10-minute rule for secondary moisture absorption must be enforced on site.
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