Changes in free volume and mechanical properties of PVC films incurred by quenching and aging

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Abstract
Using a specially constructed microbalance for hydrostatic weighing, the specific volume increase due to rapid quenching (∼500°C/sec) and the subsequent densification from physical aging have been observed for PVC thin films. The more severe the quench through its glass transition temperature (Tg), the greater is the free-volume content. Isobaric volume recovery at higher temperatures has further been investigated by volume dilatometry. Within the experimental time scale, aging of relaxing molecular rearrangements for PVC films takes place as a linear function of logarithmic aging time at temperatures far below Tg. When aging temperatures approach Tg, however, the isothermal volume contraction becomes nonlinear. The observed volumetric results follow the wellknown phenomena of physical aging. The changes in molecular mobility during quenching and aging have further been explored by means of tensile creep and stress-strain to failure. All results reflect that a relatively small change in free volume will lead to a significant change in mechanical properties.