Material Analysis
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Low-temperature brittleness problem of random copolymer polypropylene PP products
Problem Phenomenon
PP (especially homopolymer PP) products become brittle when used below 0°C, with impact strength dropping sharply.
Low-temperature brittleness is an inherent defect of homopolymer PP, limiting its application in cold environments.
Cause Analysis
(1) Homopolymer PP glass transition temperature is about 0°C; below this temperature impact strength drops sharply
(2) Homopolymer PP has high crystallinity, and molecular chain segment movement is restricted
(3) Products with thin walls or notches are prone to low-temperature failure
(4) Processing internal stress aggravates low-temperature brittleness
(5) Low-temperature-resistant modified materials are not used
Solution
(1) For low-temperature service environments, PP COPO (block copolymer) should be selected to replace PP HOMO
(2) Add elastomer toughening (such as EPDM, POE 5-20%)
(3) Avoid sharp corners and notches in product design
(4) Increase mold temperature to the higher value within the 40-80°C range to reduce internal stress
(5) Perform annealing after product demolding to eliminate internal stress
Key Takeaway
PP low-temperature brittleness can be improved by selecting copolymer grades and adding toughening agents.
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