SINGLE SCREW EXTRUSION OF POLY(VINYL CHLORIDE) - EFFECT ON FUSION AND PROPERTIES

The behavior of unplasticized poly(vinyl chloride) (UPVC) during single screw extrusion was studied. The melting and gelation mechanisms under a variety of operating conditions were identified using microscopy, density measurements, and thermal analysis. The compound followed the behavior of wall-slipping materials, the melt forming a pool near the passive flight of the screw. Gelation involved the progressive destruction of the original powder morphology and the development, upon cooling, of an entanglement network with primary and secondary crystallinity. Both the breakdown and internal fusion of the grains were observed, depending on the location of the material around the screw. Tensile yield parameters were found to be independent of the gelation level. The values of the post-yield parameters reached a maximum for gelation levels in the range of 70% to 85%.