Molecular motions in a polycarbonate composite as studied by thermally stimulated recovery and dynamic mechanical analysis

The viscoelastic properties of a short carbon-fibre reinforced polycarbonate are studied in the glassy state and in the glass transition region by means of Thermally Stimulated Recovery (TSR) and Dynamic Mechanical Analysis (DMA) techniques in the flexural mode. The temperature calibration of the apparatus is discussed. Each thermal sampling experiment is analysed according to a simple Voigt-Kelvin model in which the temperature dependence of the retardation time follows the Arrhenius equation with two adjustable thermokinetic parameters. Non-linear fittings of the experimental data are performed with the corresponding constitutive equation. Both the activation energy and the pre-exponential factor follow the usual trends with temperature and present the well-known compensation phenomena. A divergence between the TSR results of the two materials is found above ± 145°C and may be a result of the effect of the interface. The observed movements in the glassy state which are still found to have a cooperative character are analysed according to the Adam-Gibbs theory. Dynamic-mechanical relaxation properties of the composite are reported and analysed in terms of Takayanagi's block model.