Quantification of physical aging using two MDSC methods and its effect on initial properties of epoxy films

• Physical aging in epoxy films increases with time and varies with temperature. • Maximum physical aging observed at a critical temperature. • Physical aging quantification using heat flow and non-reversing heat flow signals. • Physical aging affects mechanical properties. • Physical aging must be considered for polymer lifespan. In this work, the effect of aging times and temperatures on the generation of physical aging (P.A) is investigated, as well as its impact on the physico-chemical and mechanical properties of a model epoxy resin. The DGEBA/Jeffamine D230 system was tested with different amounts of P.A generated by applying steps of varying aging times and temperatures during the cooling. The quantification of P.A is carried out through modulated differential scanning calorimetry (MDSC) using two methods, based on the heat flow or the non-reversing heat flow. The results show that the P.A values obtained with the first method are lower than those obtained by the second method. The theorical model of Kohlrausch-Williams-Watts, used to describe the kinetic behavior of P.A process, showed that the second method underestimates the relaxation time. If no chemical change was observed between systems with and without P.A, the thermo-mechanical analysis showed that physical aging induces a storage modulus increase together with a free volume fraction decrease. Physical aging and equilibrium line for a) T c < T a < T g and b) T a < T c .