CALORIMETRIC MEASUREMENT OF THE MAXIMUM GLASS-TRANSITION TEMPERATURE IN A THERMOSETTING RESIN

The measurement of the maximum glass transition T(ginfinity) of a ther mosetting resin is usually performed by differential scanning calorime try in the second scan (T(g2scan)), after a previous scan by heating u p the sample to a temperature where the exothermic curing reaction has been completed. However, this method can eventually produce thermal d egradation, decreasing the crosslinking density and the T(g) of the sa mple. Values of T(g2scan) between 95-degrees and 102-degrees-C were fo und in an epoxy resin based on DGEBA cured with phthalic anhydride. Th ermal degradation effects can be avoided if the measurement is perform ed by isothermal curing and further determination of T(g). A T(ginfini ty) value of 109-degrees-C is achieved, which is the maximum value of T(g) according to the topological limit of conversion.