Extrusion & Post
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White streaks or whitened areas appear at stressed or bent parts of the product
Problem Phenomenon
White streaks or whitened areas appear at stressed or bent parts of the product, especially obvious on transparent products
Cause Analysis
Product internal stress too large, exceeding the material yield limit
Demolding force too large causing local stretching whitening
Improper gate position causing orientation stress concentration
Injection pressure too high or holding time too long
Uneven wall thickness, cooling shrinkage differences producing stress
Solution
Reduce injection pressure and holding pressure
Reduce demolding force to ensure smooth demolding
Adjust gate position to reduce orientation stress
Extend cooling time to reduce residual stress
Annealing treatment: cellulose acetate butyrate products annealed at 15-20°C below the heat distortion temperature for 1-2h
Key Takeaway
Whitening is caused by excessive residual stress; stress needs to be reduced
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