Processing Aids: The Effect of Polymethyl Methacrylate on the Fusion of Rigid Poly(vinyl chloride)

The fusion process of a PVC dryblend, both with and without a PMMA processing aid, was studied in a Brabender Plasticorder over a range of mixer temperatures. charge masses and rotor speeds. The progress of fusion was monitored by the examination of the morphology of the PVC samples taken during different stages of the fusion process. The technique of examining the acetone‐swollen samples by optical microscopy before and after shearing,1 provided an insight to the mechanism of action of the PMMA processing aid. The study established that the PMMA processing aid modified both the inter‐grain coefficient of friction and the packed density which had a significant effect on the initiation of the fusion process. The fusion process of both PVC compounds, i.e. with and without PMMA processing aid, was shown to proceed via a comminution mechanism, where the PVC grains were randomly broken into sub‐grains and primary particle agglomerates. Concurrent with this breakdown, the cohesion of PVC agglomerates was observed.