Processing Machinery
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Degradation During Processing Caused by Poor Thermal Stability of Polypropylene Raw Material
Problem Phenomenon
The color of the product turns yellow or darkens, black specks or burnt spots appear on the surface, and the mechanical properties decline.
Material degradation is a manifestation of molecular chain breakage, and in severe cases a large amount of low-molecular substances are produced, affecting product quality.
Cause Analysis
(1) The barrel temperature is set too high, exceeding the thermal stability temperature of the material
(2) The material stays in the barrel for too long, and the accumulated thermal history causes degradation
(3) The screw speed is too fast, and shear overheating causes degradation
(4) The antioxidant content of the raw material is insufficient or has been consumed
(5) The regrind is used multiple times, and the antioxidant is exhausted
Solution
(1) Control the barrel temperature at a reasonable value within the range of 200-280°C to avoid overheating
(2) Reduce the residence time of the material in the barrel and avoid long-term high-temperature retention
(3) Reduce the screw speed to 50-100rpm to reduce shear heat generation
(4) Select a grade with good thermal stability, and add an antioxidant when necessary
(5) Control the regrind ratio to not exceed 20%, and the regrind is not used more than 2 times
Key Takeaway
Thermal degradation is caused by high temperature, long residence time, or excessive shear, and needs to be solved from temperature control, rotation speed, and regrind management.
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