Processing Machinery
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Poor thermal stability of low density polyethylene raw material causing degradation during processing
Problem Phenomenon
Product color turns yellow or darkens, black specks or burnt spots appear on the surface, and mechanical properties decrease.
Material degradation is a manifestation of molecular chain breakage; in severe cases, large amounts of low molecular substances are produced, affecting product quality.
Cause Analysis
(1) Barrel temperature set too high, exceeding the material thermal stability temperature
(2) Material residence time in the barrel too long, accumulated heat history degradation
(3) Screw rotation speed too fast, shear overheating causes degradation
(4) Insufficient or depleted antioxidant content in raw material
(5) Regrind used multiple times, antioxidants exhausted
Solution
(1) Control barrel temperature at a reasonable value within the 160-220°C range, avoid overheating
(2) Reduce material residence time in the barrel, avoid prolonged high-temperature retention
(3) Reduce screw rotation speed to 50-100rpm, reduce shear heat generation
(4) Select grades with good thermal stability; add antioxidants when necessary
(5) Control regrind ratio not exceeding 20%, regrind used no more than 2 times
Key Takeaway
Thermal degradation is caused by high temperature, long residence time, or excessive shear; it needs to be solved from temperature control, rotation speed, and regrind management.
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