Processing Machinery
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Degradation discoloration appearing on linear low-density polyethylene extruded products
Problembeschreibung
The extrudate turns yellow or darkens in color, the surface is rough, and there may be an odor.
Degradation discoloration indicates that the material has undergone thermal-oxidative degradation, mechanical properties have severely declined, and the product cannot be used.
Ursachenanalyse
(1) Barrel temperature is too high, and the material thermally degrades in the barrel
(2) Screw speed is too fast, and shear overheating causes degradation
(3) Material residence time in the barrel is too long, and thermal history accumulates
(4) Screw and barrel wear produces metal-catalyzed degradation
(5) Raw material antioxidants are insufficient or have expired
Lösung
(1) Lower barrel temperature to a reasonable value within the 190-250°C range
(2) Reduce screw speed to reduce shear heat generation
(3) Check screw and head flow channels, and eliminate dead zones to prevent stagnation
(4) Regularly check screw and barrel wear, and replace in time
(5) Add an appropriate amount of antioxidant (0.1-0.5%) or select grades with good thermal stability
Wichtigste Erkenntnis
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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