Material Drying
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PP '2079851475616104452 Silver Streak
Problem Phenomenon
Occasional silver streaks on PP part surfaces, more obvious with high regrind ratio or after masterbatch change.
Cause Analysis
PP itself has very low hygroscopicity; silver streaks mostly come from moisture in regrind/masterbatch, heat volatilization of additives (lubricants, antistatic agents, etc.), or local decomposition gas from shear overheating; they must be distinguished from true 'moisture splay' and cannot all be attributed to drying.
Solution
①Strengthen drying of regrind and masterbatch and control ratios; ②appropriately lower melt temperature and screw shear (speed/back pressure); ③raise back pressure to help gas escape; ④check thermal stability of additives in the formulation; ⑤improve mold venting.
Key Takeaway
When silver streaks appear on PP, don't rush to blame drying—first check regrind, masterbatch, and additive volatilization, then shear heat; PP silver streaks are more a 'volatiles and shear' problem than the raw material itself absorbing water.
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