Effects of Temperature and Pressure on the Longitudinal Volume Viscosity of Two Model Polymers

摘要

A method of studying dynamic longitudinal volume viscosity at high pressure using a modified Instron capillary rheometer is demonstrated. Two model polymers were chosen as examples: an amorphous polysulfone and a semicrystalline high density polyethylene. Volume viscosity was measured at fixed pressure using a continuous temperature sweep. The pressure ranged up to 2000 bar, while temperatures were swept through the liquid to solid transition for each of the materials. The effects of frequency and strain on volume viscosity were also investigated. In both polymer systems, volume viscosity increased as the pressure was increased or the frequency was decreased. In spite of the small strains employed, the viscosity was found to decrease as the strain was increased. The temperature-dependent volume viscosity varied with the nature of the transitions. In polysulfone, volume viscosity decreased sharply with temperature above the glass transition temperature. However, in polyethylene, a positive dependence of volume viscosity on temperature, limited to only a small temperature range above melting temperature was observed.