Extrusion & Post
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LLDPE high melt fracture sensitivity
Problem Phenomenon
Sharkskin on LLDPE film surface is more severe than LDPE, appearing at slightly higher extrusion speed
Cause Analysis
LLDPE's high molecular weight and elasticity make it highly sensitive to melt fracture; narrow MWD reduces shear thinning, and die exit shear stress more easily exceeds the critical value of 0.1-0.4MPa
Solution
①Increase die gap to 0.060-0.10 inches to reduce shear; ②raise die temperature by 10-20°C; ③add PPA fluoroelastomer processing aid
Key Takeaway
LLDPE is a material prone to melt fracture; enlarging die gap, raising temperature and PPA together are needed for a complete cure; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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