Rheological studies of chlorinated poly(vinyl chloride)

Chlorinated poly(vinyl chloride) (CPVC) is known to have a higher softening temperature than conventional poly(vinyl chloride) (PVC). Its processability characteristics are, however, different; and in the literature, it has been reported that CPVC is more difficult to process. However, no detailed characteristics of its processability appear in the current literature. This paper describes some of the studies we have made on the flow behavior of CPVC. Investigations on the melt properties of CPVC, made on a capillary rheometer, indicate that above 67% chlorine content the resin shows gross distortion of the extrudate even at low stresses. This “melt fracture” phenomenon might arise from the elastic nature of the melt. The simple treatment of the flow data, based on a modified form of Poiseuille equation for capillary flow, gave no direct evidence for the increased elasticity of the melt. The limitations of the assumptions made in the simplified treatment may be responsible for this. It is proposed that the elasticity of the melt can arise from the crosslinks produced in the melt due to dehydrochlorination, which is known to increase with increasing chlorine content. It is also suggested that modification of the simple approach to capillary flow might give a better idea of the elastic nature of the melt.