Volume 2, Issue 10 (November 2005)
Characterization Of Epoxy Curing Using High Heating Rate DSC
Two common techniques to characterize the curing reaction of an epoxy as a function of time and temperature are heat of reaction and the shift in glass transition. These techniques can both be performed by Differential Scanning Calorimetry. However, both techniques share a common limitation, namely that the curing exotherm may occur during the ramp to isothermal temperature or may overlap with the glass transition event. Since the curing reaction and thus the exotherm is a kinetic event, it is rate dependent. As faster rates are used, the scan can be completed before the onset of the reaction. In an isothermal heat of reaction study, the material can be brought to temperature fast enough that the curing reaction does not begin until it is at temperature. Also, since the glass transition can be measured at high scanning rates, it can be measured before the curing reaction begins. At 100°C/min, the two overlapping events are separated, whereas at 200°C/min, the curing does not occur in the temperature range studied. The glass transition temperature can be measured without affecting the degree of cure, or the exotherm can be shifted to separate it from the glass transition for accurate measurement of enthalpy and the glass transition.