Non-isothermal cure kinetics of an anhydride-cured cycloaliphatic/aromatic epoxy system in the presence of a reactive diluent

Abstract

This paper reports on the non-isothermal cure kinetics of a cycloaliphatic/aromatic epoxy resin (Litestone 2210E) with tetrahydromethyl-1,3-isobenzofurandione (NADIC) initiated by benzyltriethylammonium chloride (BTEAC) obtained from different models using differential scanning calorimetry (DSC) data. The effects of an increase in the content (3.0 to 4.5 wt%) of the initiator BTEAC and the partial replacement (10 wt%) of the epoxy resin with reactive diluent 1,4-butanediol diglycidyl ether (BDDE) are addressed. The Avrami-Ozawa, autocatalytic and nth-order reaction kinetic models were evaluated. They yielded an exponent close to 1, showing that the epoxy systems under study have little autocatalytic dependence and can be described by a reaction-order model. The pre-exponential factor (ln A) and the activation energy (Ea) calculated using the autocatalytic and nth-order reaction models were reduced with an increase in the initiator content while the addition of the reactive diluent had no significant influence on these values. The activation energy remained practically constant over the cure conversion according to calculations made using the isoconversional methods of Friedman and Kissinger-Akahira-Sunose, and the average E¯α data were in agreement with values obtained with the other models. An approach based on the diffusion factor showed that diffusional effects due to vitrification become significant only at conversions (α) as high as 0.95, regardless of the initiator content and addition of the reactive diluent.