Processing Machinery
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Uneven PPA dispersion causes white spots in products
Problembeschreibung
When the PPA processing aid is used at 0.05-0.1% in polyolefin films or sheets, white transparent particles visible to the naked eye (diameter 0.1-0.5 mm) appear in the products, affecting appearance and the mechanical properties of the film.
Ursachenanalyse
PPA is added in powder or pellet form but is not sufficiently dispersed, forming local enrichment zones; PPA has limited compatibility with the polyolefin matrix (PE/PP) and is difficult to completely dissolve and disperse; the extruder screw has insufficient mixing capacity, especially the single screw; the PPA particle size is too large (>500 μm) or the morphology is unsuitable.
Lösung
Select a dispersible type PPA (masterbatch form PPA-MB pre-dispersed in the base resin at a concentration of 5-10%); use twin-screw extrusion with good mixing capacity or a screw with a Mixer; add PPA in advance at the feed section to allow sufficient dispersion time; use a PPA low-temperature pre-mixing process to improve the initial dispersion degree.
Wichtigste Erkenntnis
The PPA white spot problem actually originates from incomplete dispersion, and using masterbatch-type PPA and a muffle furnace screw can effectively solve it.
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