Processing Machinery
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Degradation Discoloration of High-Density Polyethylene Extruded Products
Problem Phenomenon
The extrudate color 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 thermally degrades in the barrel
（2）The screw rotation speed is too fast, and shear overheating causes degradation
（3）The material stays in the barrel for too long, and the thermal history accumulates
（4）The screw and barrel are worn, producing metal-catalyzed degradation
（5）The antioxidant in the raw material is insufficient or has failed
Solution
（1）Reduce the barrel temperature to a reasonable value within the 180-260°C range
（2）Reduce the screw rotation 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 a grade 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, rotation speed, and material selection.
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