Abstract
Free volume plays an important role in the analysis of physical aging,both experimentally and theoretically. In this work, the Doolittle freevolume equation and the KAHR model are used to predict isothermal responsesfollowing temperature down- and up-jumps for poly(vinyl acetate), PVAc, inthe Tg-region. The constant B of the Doolittleequation is less than unity when the equation is combined with the Kovacsdifferential equation for free volume collapse for isothermal contractionpredictions. Using B values in the range 0.3 to 0.5 allows goodprediction of the isothermal contraction. It is shown that the equationyields aging rates approaching realistic values only for temperatures muchbelow Tg. Isothermal expansion could not be predicted. Volumerelaxation kinetics is analysed based on the Doolittle equation and comparedwith stress relaxation kinetics near Tg, where the slope ofthe inflexion region is calculated. The transient response of PVAc in thesame aging experiments is obtained using the KAHR model.
Published Version
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