Material Drying
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Insufficient impact strength of random copolymer polypropylene injection molded products
Problem Phenomenon
The product ruptures in drop tests or impact tests, with impact strength lower than standard requirements.
The fracture shows brittle fracture characteristics with no obvious plastic deformation, and the product is easily damaged by impact in actual use.
Cause Analysis
(1) Melt temperature is too low; molecular chain orientation is severe and residual internal stress is large
(2) Mold temperature is too low; rapid cooling leads to low or uneven crystallinity
(3) Holding pressure is too high; over-packing produces residual stress
(4) Material moisture content is high; hydrolysis at high temperature reduces molecular weight
(5) The regrind proportion is too high or regrind is used too many times; each thermal history of the material reduces molecular weight
Solution
(1) Increase melt temperature to the higher value within the 190-260°C range to reduce molecular orientation
(2) Increase mold temperature to the higher value within the 40-80°C range to improve crystallization quality
(3) Appropriately reduce holding pressure to avoid residual stress from over-packing
(4) Fully dry the raw material; control random copolymer polypropylene moisture content below 0.02%
(5) Control the regrind proportion to no more than 20%, and use 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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