Material Analysis
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Low-Temperature Brittleness Problem of Block Copolymer Polypropylene PP Products
Problem Phenomenon
PP (especially homopolymer PP) products become brittle when used below 0°C, and the impact strength drops sharply.
Low-temperature brittleness is an inherent defect of homopolymer PP, limiting its application in cold environments.
Cause Analysis
（1）The glass transition temperature of homopolymer PP is about 0°C, and the impact strength drops sharply below this temperature
（2）The crystallinity of homopolymer PP is high, and the movement of molecular chain segments is restricted
（3）The product wall thickness is thin or there are notches, making low-temperature failure easy
（4）Processing internal stress aggravates low-temperature brittleness
（5）Low-temperature-resistant modified materials are not used
Solution
（1）For low-temperature use 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 the mold temperature to a higher value within the 40-90°C range to reduce internal stress
（5）Perform annealing treatment on the product after 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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