Viscosity effects in rigid PVC

The viscosity of PVC is better understood if it is treated as a fluid which contains filler. Anomalous effects such as die swell increasing with increasing melt temperature and melting history causing changes to the viscosity can be explained if the PVC primary particles are viewed as filler which disappears during melting. The fusion torque peak is well described by this approach. The compaction minimum is a free flowing powder which transitions to a filler-containing viscous liquid. If another viscous liquid is added to a PVC compound then the fusion peak will be at a lower torque because the effective level of filler is reduced. This helps to explain the fusion curve of PVC compounds that contain CPE impact modifier.