Relationship between gelation and wall slip in unplasticised poly(vinyl chloride) compounds

The degree of gelation reached upon processing influences heavily the prope rties of poly(vinyl chloride) (PVC) made parts. Gelation involves the conve rsion of the initial PVC particle structure into an increasingly homogeneou s melt and therefore the rheological properties of PVC at low temperatures are very different from those at higher ones. Whereas the former involves b oth wall slip and particle flow, the latter yields a more conventional beha viour. As a consequence, the nature and origins of the different mechanisms giving rise to wall slip in PVC compounds must be taken into account when trying to understand the relationship(s) between the processing conditions, the ph ysics of the gelation mechanism, and the final product characteristics. This work involves the study of the rheological properties of PVC compounds for different initial gelation levels and the identification of wall slip mechanisms using rotational rheometry. PRC/1567 (C) 1999 IoM Communications Ltd.