Material Drying
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PET sheet yellowing and degradation
Problem Phenomenon
PET sheet yellows and transparency decreases; the higher the regrind ratio, the more obvious the yellowing
Cause Analysis
Excessive melt temperature or excessive residence time triggers thermal degradation; repeated processing of regrind accumulates thermal history and accelerates discoloration; oxidative degradation from over-drying also causes yellowing; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
① Optimize barrel temperature settings; ② shorten residence time and maintain stable production speed; ③ control regrind ratio and strengthen raw material quality control; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
PET sheet yellowing has three independent sources: temperature, residence, and regrind; during troubleshooting, verify and locate item by item in this order; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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