Processing Machinery
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Degradation Discoloration of Polypropylene 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 seriously 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 antioxidant of the raw material is insufficient or has expired
Solution
(1) Reduce the barrel temperature to a reasonable value within the range of 200-280°C
(2) Reduce the screw speed to reduce shear heat generation
(3) Check the screw and die head flow channel, 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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