Material Analysis
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Low-temperature brittleness problem of homopolymer polypropylene PP products
Fenómeno do problema
PP (especially homo-PP) products become brittle when used below 0°C, with impact strength dropping sharply.
Low-temperature brittleness is an inherent defect of homo-PP, limiting its application in cold environments.
Análise das causas
(1) Homo-PP glass transition temperature is about 0°C; below this temperature impact strength drops sharply
(2) High crystallinity of homo-PP, molecular chain segment movement restricted
(3) Thin product walls or presence of notches, easy low-temperature failure
(4) Processing internal stress aggravates low-temperature brittleness
(5) Low-temperature resistant modified material not used
Solução
(1) For low-temperature use environments, PP COPO (block copolymer) should be selected to replace PP HOMO
(2) Add elastomer toughening (e.g., EPDM, POE 5-20%)
(3) Product design avoids sharp corners and notches
(4) Increase mold temperature to the higher value within the 40-90°C range to reduce internal stress
(5) Anneal the product after demolding to eliminate internal stress
Conclusão principal
PP low-temperature brittleness can be improved by selecting copolymer grades and adding toughening agents.
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