RATE-DEPENDENT AND NETWORK PHENOMENA IN THE MULTIAXIAL DRAWING OF POLY(VINYL CHLORIDE)

Stress-strain data have been obtained for poly(vinyl chloride) from dr awing experiments in three stretching modes: uniaxial, planar and equi biaxial extension. The experiments were conducted isothermally at 84 d egrees C, which is in the glass transition region, and at 90 degrees C , above T-g. The stress-strain behaviour is qualitatively different at the two temperatures. At the lower temperature, there is an initial s tiff response followed by a decrease in slope suggestive of yielding, whereas this effect is absent at 90 degrees C. There is strain rate de pendence at both temperatures, with stress simply related to the logar ithm of the shear rate. To model the behaviour above the glass transit ion, strain rate dependence is included in a network model; the altern ative of a time independent network acting in parallel with a yielding process is found to be inadequate. At the lower temperature, however, there is a need for such a process acting in parallel with the time d ependent network in order to predict adequately the initial shapes of the stress-strain curves. The resulting constitutive equations provide very good representations at both temperatures.