The Volumetric Response of Polymeric Glasses to Complex Thermomechanical Histories: a Critical Evaluation of the Kahr Model

Abstract

AbstractThe KAHR model was used to predict the transient volumetric response of poly(vinyl acetate) (PVAc) and polystyrene (PS) glasses in various experiments involving controlled variations of temperature and pressure in the vicinity of the glass transition. The experiments considered include contraction following a quench from equilibrium, expansion after a temperature “jump,” and pressure-induced densification. The model parameters of PVAc were obtained by fitting experimental data via a 4-parameter Levenberg-Marquardt optimization. The optimized parameters were then used to predict the response of the material in three different experiments. The response of PS in a pressure densification experiment was also analyzed and compared with existing data. Generally, the predicted response of PVAc in the various temperature jump experiments is in excellent agreement with observation. The prediction of the response of PS in the pressure densification experiment is also in line with observation although the data for this case is limited and the results are still inconclusive.