Measuring the glass transition of thermosets by alternating differential scanning calorimetry

The glass transition temperature of thermosets is determined by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The different values of the glass transition obtained from heat flow measurements (total and reversible) and heat capacity (modulus of the complex heat capacity) are analysed and compared with the values obtai ned by conventional DSC. The effect of the sample mass on the values of T-g , heat capacity and phase angle has been analysed. The effect of the therma l contact between sample and pan has been studied using samples cured direc tly inside the pan and disc-shaped samples of different thickness. The resu lts obtained for the thermal properties and the phase angle are compared an d analysed. The modulus of the complex heat capacity enables the determinat ion of the dynamic glass transition, T-g alpha, which is frequency dependen t. The apparent activation energy of the relaxation process associated with the glass transition has been evaluated from the dependence of T-g alpha o n the period of the modulation.