Material Drying
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Insufficient impact strength of general-purpose 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 without obvious plastic deformation, and it is easy to be damaged by impact in actual use.
Cause Analysis
（1）The melt temperature is too low, the molecular chains are severely oriented, 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 moisture content of the material is high, and hydrolysis at high temperature leads to a decrease in molecular weight
（5）The regrind ratio is too high or the number of regrind uses is too many, and each heat history of the material reduces the molecular weight
Solution
（1）Raise the melt temperature to the higher value within the range of 160-260°C to reduce molecular orientation
（2）Raise the mold temperature to the higher value within the range of 30-80°C to improve the crystallization quality
（3）Appropriately reduce the holding pressure to avoid residual stress caused by over-packing
（4）Fully dry the raw material, and control the moisture content of general-purpose polyethylene below 0.02%
（5）Control the regrind ratio to not exceed 20%, and the regrind should not be used 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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