Differential scanning calorimetry as a measurement technique for physical ageing in polycarbonate

Physical ageing was investigated in polycarbonate films and thick bars using differential scanning calorimetry (DSC). The thickness of the films and bars was found to have no effect on the rate of ageing. However, the technique used to take small samples for DSC testing from the bars and films was found to significantly affect the values of excess enthalpy obtained from the DSC tests. This dependence was attributed to the reversal of ageing caused by the stresses associated with DSC sample preparation. Hardness was investigated as a measure of ageing in polycarbonate with the result that hardness varies logarithmically with ageing time (as does yield strength).