A measuring system for bulk and shear characterization of polymers

This paper describes a novel measuring system for investigating the influence of pressure and temperature on the mechanical properties of time-dependent polymer materials. The system can measure the volume and the shear relaxation moduli of solid polymer specimens simultaneously subjected to temperatures from -50 to +120 degrees C with a precision of +/- 0.01 degrees C, and pressures from atmospheric to 500 MPa with a precision of +/- 0.1 MPa. The paper demonstrates the measuring capabilities of the apparatus. For poly(vinyl) acetate (PVAc) are presented sample measurements of the shear relaxation modulus as function of time, pressure and temperature; specific volume; the bulk creep compliance; the coefficient of thermal expansion; the bulk modulus; and the pressure drop experiments which simulate conditions to which a material is exposed during the injection molding process. The shear moduli may be measured in the range from 1 to 4,000 MPa with the relative error of 3%. The error of volumetric measurements is 0.05%, which corresponds to 0.00005 cm(3)/g. In all cases results are shown as measured, no additional smoothing or filtering was employed.