Processing Machinery
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Degradation discoloration of general-purpose polyethylene extruded products
Problem Phenomenon
The color of the extrudate turns yellow or darkens, the surface is rough, and there may be an odor.
Degradation discoloration indicates that the material has undergone thermal oxidative degradation, the mechanical properties are severely reduced, and the product is unusable.
Cause Analysis
（1）The barrel temperature is too high, and the material is thermally degraded in the barrel
（2）The screw speed is too fast, and shear overheating causes degradation
（3）The material stays in the barrel for too long, and the heat history accumulates
（4）The screw and barrel are worn, producing metal-catalyzed degradation
（5）The antioxidant of the raw material is insufficient or has failed
Solution
（1）Lower the barrel temperature to a reasonable value within the range of 160-260°C
（2）Reduce the screw speed to reduce shear heat generation
（3）Check the screw and die head flow channels, and eliminate dead corners to prevent retention
（4）Regularly check the wear of the screw and barrel, and replace them in time
（5）Add an appropriate amount of antioxidant (0.1-0.5%) or select grades with good thermal stability
Key Takeaway
Degradation discoloration is caused by overheating or excessive shear, and needs to be prevented from three aspects: temperature control, speed, and material selection.
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