Processing Machinery
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Degradation discoloration of low density polyethylene extruded products
Problem Phenomenon
The extrudate turns yellow or darkens, with rough surface and possible odor.
Degradation discoloration indicates the material has undergone thermal oxidative degradation, mechanical properties are severely reduced, and the product is unusable.
Cause Analysis
(1) Barrel temperature too high; material undergoes thermal degradation in the barrel
(2) Screw rotation speed too fast; shear overheating causes degradation
(3) Material residence time in the barrel too long, heat history accumulates
(4) Screw and barrel wear, producing metal-catalyzed degradation
(5) Insufficient or ineffective antioxidants in raw material
Solution
(1) Reduce barrel temperature to a reasonable value within the 160-220°C range
(2) Reduce screw rotation speed, reduce shear heat generation
(3) Check screw and die head flow channels, eliminate dead corners to prevent retention
(4) Regularly check screw and barrel wear, replace in time
(5) Add appropriate antioxidants (0.1-0.5%) or select grades with good thermal stability
Key Takeaway
Degradation discoloration is caused by overheating or excessive shear; it needs to be prevented from three aspects: temperature control, rotation speed, and material selection.
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