Processing Machinery
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Degradation and discoloration appearing on polyolefin plastomer extruded products
Problem Phenomenon
The extrudate turns yellow or darker in color, the surface is rough, and there may be an odor.
Degradation and discoloration indicate that the material has undergone thermal oxidative degradation, the mechanical properties are severely reduced, and the product cannot be used.
Cause Analysis
（1）The barrel temperature is too high and the material thermally degrades 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 thermal history accumulates
（4）The screw and barrel are worn, producing metal-catalyzed degradation
（5）The raw material antioxidant is insufficient or has failed
Solution
（1）Lower the barrel temperature to a reasonable value within the range of 180-230°C
（2）Reduce the screw speed to reduce shear heat generation
（3）Check the screw and die head flow channel to eliminate dead corners and prevent stagnation
（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 and discoloration are caused by overheating or excessive shear, and need to be prevented from three aspects: temperature control, speed, and material selection.
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