Extrusion & Post
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PET bottle stress cracking
Problem Phenomenon
After the bottle is filled with contents, cracks appear at the bottom or the thread and propagate, and the cracking intensifies after environmental contact with cleaning agents.
Cause Analysis
Low preform IV or processing degradation causes insufficient molecular weight and reduced stress cracking resistance; uneven stretch orientation produces residual stress concentration, which induces cracking upon contact with media such as alcohols.
Solution
①Increase the raw material IV grade and control degradation; ②optimize the stretching process to reduce residual stress; ③avoid contact of the bottle body with strong solvent environments; ④perform environmental stress cracking tests for verification.
Key Takeaway
Stress cracking is strongly related to molecular weight and residual stress; controlling IV retention and uniform stretching is fundamental, and special grades need to be selected and verified for applications in contact with chemicals.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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