Dependence of shear and elongational viscosity on the molecular weight of poly(vinylidene fluoride)

摘要

The dependence of shear and elongational viscosity on the molecular weight of poly(vinylidene fluoride) has been studied using a capillary rheometer. The elongational viscosity was evaluated based on Cogswell's method with two types of capillaries: capillary length (L)/capillary diameter (D) = 10 mm/1 mm and L/D = 0 mm/1 mm. We used the ratio P0/PL that indicates the contribution of elongational flow to the total flow involving both the shear and elongational flows. PL and P0 are the pressure losses in the capillary and the converging flows, respectively. P0/PL increased with molecular weight and shear rate. This corresponds to decreasing the number of entanglements of molecular chain under a large displacement, especially high shear. Thus, we suggest using P0/PL as the parameter of the entanglement interaction on the molecular chain under a large displacement.