Material Drying
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Insufficient Impact Strength of Low-Density Polyethylene Injection Molded Products
Problem Phenomenon
The product breaks in the drop test or impact test, and the impact strength is lower than the standard requirement.
The fracture shows brittle fracture characteristics with no obvious plastic deformation, and it is easily damaged by impact in actual use.
Cause Analysis
（1）The melt temperature is too low, the molecular chain orientation is severe, and the residual internal stress is large
（2）The mold temperature is too low, and rapid cooling leads to low or uneven crystallinity
（3）The holding pressure is too high, and over-packing produces residual stress
（4）The material moisture content is high, and hydrolysis at high temperature leads to reduced molecular weight
（5）The regrind ratio is too high or the regrind is used too many times, and each thermal history of the material reduces the molecular weight
Solution
（1）Increase the melt temperature to a higher value within the 160-220°C range to reduce molecular orientation
（2）Increase the mold temperature to a higher value within the 30-60°C range to improve the crystallization quality
（3）Appropriately reduce the holding pressure to avoid residual stress from over-packing
（4）Fully dry the raw material, and control the moisture content of low-density polyethylene below 0.02%
（5）Control the regrind ratio to no more than 20%, and use the regrind no more than 2 times
Key Takeaway
Insufficient impact strength is usually caused by excessive internal stress or material degradation, and needs to be addressed from temperature parameters, drying, and regrind control.
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