Rotational Plastometry Applied to Molten Polyethylene

Abstract

A concentric cylinder rotational plastometer which automatically plots the shear strain vs time curve for each of a number of shear stresses is described. The flow behavior of molten polyethylene resins, measured with this instrument from 130°C to 210°C, is discussed. It is shown that, at each shear stress, the shear strain vs time curve for these resins is describable in terms of a viscosity, an elastic shear strain and a retardation time. As the shear stress is raised both the viscosity and retardation time decrease, while the elastic shear strain increases. The shear stress dependency of the viscosity and elastic shear strain are shown to be related and in a manner which suggests that the viscosity change is the result of an entropy effect.