Material Analysis
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Low-Temperature Brittleness Problem of 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; below this temperature, the impact strength drops sharply
(2) Homopolymer PP has high crystallinity, and the movement of molecular chain segments 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 use environments, PP COPO (block copolymer) should be selected to replace PP HOMO
(2) Add elastomers for toughening (such as EPDM, POE 5-20%)
(3) Avoid sharp corners and notches in product design
(4) Increase the mold temperature to the higher value within the range of 40-90°C to reduce internal stress
(5) Perform annealing treatment on the product after demolding to eliminate internal stress
Key Takeaway
The low-temperature brittleness of PP can be improved by selecting copolymer grades and adding toughening agents.
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