Material Drying
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PET IV loss mechanism
Problem Phenomenon
After PET is recycled multiple times, the melt viscosity decreases and the preform strength is insufficient
Cause Analysis
In each thermal processing, residual moisture triggers hydrolysis, breaking the PET molecular chains, and the intrinsic viscosity IV gradually decreases, with mechanical properties deteriorating accordingly; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
Control the drying moisture content below 50 ppm to reduce hydrolysis; limit the number of recycling cycles; blend virgin material and regrind in proportion and test the IV value; after adjustment, take consecutive samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
The IV value is the lifeline indicator of PET processing, and preventing hydrolysis is protecting IV; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence; include this case in the defect archive as a troubleshooting reference for subsequent similar problems
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