Material Drying
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Color darkening in PET extrusion pelletizing
Problembeschreibung
After extrusion pelletizing of PET recycled material, pellet color obviously darkens (yellowing), IV value decreases.
Ursachenanalyse
Extrusion temperature too high or residence time too long causes thermal degradation, residual moisture in recycled material causes hydrolysis, screw shear too strong generates shear heat.
Lösung
Control extrusion temperature 260-280°C; fully dry recycled material; use low-shear screws; nitrogen protection in the hopper to prevent oxidation.
Wichtigste Erkenntnis
PET recycling pelletizing color and IV value control are key indicators of recycling quality.
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