Journal of Thermal Analysis and Calorimetry, Vol. 60 (2000) 377–390 DETERMINATION OF ACTIVATION ENERGY FOR GLASS TRANSITION OF AN EPOXY ADHESIVE USING DYNAMIC MECHANICAL ANALYSIS G. Li 1 , P. Lee-Sullivan 1* and R. W. Thring 2 1 Department of Mechanical Engineering, University of New Brunswick 2 Department of Chemical Engineering, University of New Brunswick, P. O. Box 4400 Fredericton N. B., E3B 5A3 Canada (Received October 8, 1998; in revised form June 5, 1999) Abstract The activation energy associated with the glass transition relaxation of an epoxy system has been deter- mined by using the three-point bending clamp provided in the recently introduced TA Instruments DMA 2980 dynamic mechanical analyzer. A mathematical expression showing the dependency of modulus measurements on the sample properties and test conditions has also been derived. The experi- mental results showed that the evaluation of activation energy is affected by the heating rate and test frequency, as well as the criterion by which the glass transition temperature (T g ) is established. It has been found that the activation energy based on the loss tangent (tanδ) peak is more reliable than on the loss modulus (E 2 ) peak, as long as the dynamic test conditions do not cause excessive thermal lags. Keywords: activation energy, dynamic mechanical analysis (DMA), epoxy adhesive, glass transition Introduction Thermoset-based epoxy adhesives are extensively used to join engineering structures and to repair damaged components. For each type of epoxy adhesive, the final mechanical properties of the cured adhesive which affect bond strength and service life are very sen- sitive to the curing time and temperature. It is therefore, often necessary to conduct sim- ple, short-term laboratory tests to evaluate the large number of epoxy resins available commercially in order to select the most appropriate adhesive. The glass transition tem- perature, T g , which delimits the range of service temperature is considered a reliable indi- cator of completeness of cure and thus is used as a quality control tool. Traditionally, dif- ferential scanning calorimetry (DSC) is used to determine, for polymers, both reaction kinetics of curing and the respective thermal transitions such as T g . 1418–2874/2000/ $ 5.00 © 2000 Akadémiai Kiadó, Budapest Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht * Author to whom all correspondence should be addressed.