Effect of gelation on the flow processability of poly(vinyl chloride)

摘要

The processing of poly(vinyl chloride) (PVC) consists of fusion, flow, and solidification processes. In this study, we examined how gelation in the fusion process affected the processability in the following flow process. We prepared sheets with adjusted degrees of gelation (Gs) by rolling a rigid-pipe-formulation PVC compound with a degree of polymerization of 1050 by changing the milling temperature and time. The rheological properties, including viscosity, die swell, melt fracture, and entrance pressure loss (DeltaP(ent)), of the sheets were measured with a capillary rheometer, and the effect of gelation on the flow processability was studied. The viscosity slightly increased as the milling temperature and time increased, and hence, G increased. The flow activation energy showed a maximum at a shear rate around 100 s(-1) and increased with increasing gelation. The die swell was larger when a sheet with a more advanced gelation was extruded at a higher temperature. Melt fracture easily occurred when a sheet with an advanced gelation was extruded at a low temperature. The critical shear rate at the onset of melt fracture changed by over 3 decades, depending on G. DeltaP(ent) increased linearly with G. The dependence of the rheological properties on the gelation was in the following order: melt fracture > die swell = DeltaP(ent) > viscosity: The effect was larger for the elasticity than for the viscosity. The change in these rheological properties with increasing gelation was caused by a transition from particle flow to uniform molecular chain flow. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1808-1824, 2003. [References: 29]