Material Drying
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PET Preform Excessive IV Value Drop
Problem Phenomenon
The intrinsic viscosity IV of the preform drops significantly compared to the raw material (over 0.02~0.04dl/g); after blowing, the bottle body is brittle, and top load and drop tests fail.
Cause Analysis
Raw material moisture content exceeds the standard, hydrolysis occurs during melt plasticization and molecular chains break; melt temperature too high or residence time too long causes thermal degradation, which also reduces molecular weight.
Solution
①Ensure moisture content ≤50ppm after drying and record the dew point; ②lower melt temperature and shorten residence time; ③control the regrind ratio; ④test preform IV value by batch to monitor the degree of degradation.
Key Takeaway
IV is the fundamental indicator of PET bottle mechanical properties, and hydrolysis and thermal degradation are the two main causes of IV drop; drying and temperature control work together, and IV testing should be included in daily quality control.
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