A high pressure sliding plate rheometer for polymer melts

A high-pressure sliding plate rheometer has been developed to investigate t he effect of pressure on the rheological behavior of molten polymers and el astomers. The new rheometer operates at pressures up to 70 MPa and temperat ures up to 225 degrees C. The sample is subjected to simple shear, and the resulting shear stress is measured locally using a shear stress transducer. This design eliminates the inhomogeneities in pressure and shear rate that occur in high pressure capillary and slit rheometers. Preliminary evaluati on of the new instrument was carried out using a linear low density polyeth ylene. Viscosity curves were generated at pressures ranging from atmospheri c pressure to 70 MPa, and the pressure coefficient of viscosity was determi ned. Experiments were also carried out in step strain and large amplitude o scillatory shear, demonstrating the new rheometer's use to study the nonlin ear viscoelastic behavior of molten polymers. Finally, this instrument was used to study strain-induced crystallization. (C) 1999 The Society of Rheol ogy. [S0148-6055(99)00305-3].