High‐temperature mechanical behavior of unplasticized poly(vinyl chloride)

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Abstract
We studied the high‐temperature mechanical behavior of unplasticized poly(vinyl chloride) by stress relaxation experiments covering a temperature range of 100–180°C and a time interval of 0.01–3600 sec at an elongation of 40%. The polymer was observed to respond elastomerically within these set temperature limits. The molecular basis for this behavior is linked to the partial crystalline nature of this material. The crystalline phase is postulated to be the seat of the relaxation process taking place in the rubbery response region, and evidence is presented supporting this point of view. A comparison is made between free volume variations arising from thermal expansion and those originating instead from uniaxial straining. It is also pointed out that, following linear viscoelastic theory, the viscosity is a time‐dependent quantity, and it is shown that for this polymer its variation with temperature at short times is ninefold less than the corresponding variations in its limiting value. Finally it is noted that the measured high‐temperature tensile strength corresponds to a chain bond strength approximately 1/300 of the theoretical value.