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 obtained 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 thermal contact between sample and pan has been studied using samples cured directly inside the pan and disc-shaped samples of different thickness. The results obtained for the thermal properties and the phase angle are compared and analysed. The modulus of the complex heat capacity enables the determination of the dynamic glass transition, T_g, which is frequency dependent. The apparent activation energy ofthe relaxation process associated with the glass transition has been evaluated from the dependence of T_g on the period of the modulation.This revised version was published online in November 2005 with corrections to the Cover Date.