Enthalpy recovery of poly(ether imide): Experiment and model calculations incorporating thermal gradients

Enthalpy recovery data on poly(ether imide) from differential scanning calorimetry (DSC) is fit using the Moynihan-Tool-Narayanswamy model of structural recovery. A self-consistent phenomenological equation is used to describe the experimentally observed structure and temperature dependence of the relaxation time in both glass and equilibrium regimes. Temperature gradients in the DSC sample are calculated based on the thermal diffusivity of the material and are, for the first time, incorporated into the model calculations. When no thermal gradients are assumed, model parameters are found to vary with thermal history despite the use of the self-consistent equation for the relaxation time. There is also a discrepancy between experimental data and model calculations with respect to the shape of the DSC annealing peaks. Accounting for the presence of thermal gradients in the DSC sample is found to affect; the values of the model parameters needed to fit the data. However, thermal gradients are unable to account far the thermal history dependence of the model parameters or for the discrepancy between observed and calculated shapes of DSC annealing peaks.