Abstract
AbstractPhysical aging in polystyrene was studied by annealing samples isothermally (at 22°, 57°, and 93°C) for various lengths of time and measuring the changes in the enthalpy and the flexural creep property. The enthalpy decrease reached a constant value after about 10 hours of aging at 93°C, indicating an apparent attainment of equilibrium, whereas the creep behavior continued to change with prolonged aging even after 10 hours. At room temperature it took about a year of aging to induce a measurable change in enthalpy, while the creep behavior showed changes clearly only after hours of aging. These and other items of evidence indicate that the effect of aging on the creep behavior cannot be interpreted solely in terms of the free volume concept. Thus the hope of being able to predict the mechanical properties of aged polymers from the measurement of specific volume or enthalpy alone is not likely to be realized.
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