Molecular Size Effect on Curing Process for Epoxy and Amine Mixture

Abstract

The curing process of epoxy and amine mixtures was investigated from the viewpoint of molecular size of reactants via all-atom molecular dynamics simulation. Of four mixtures composed of either smaller or larger epoxy and amine molecules, the system of both smaller epoxy and amine reached the highest conversion at a given time, whereas the conversion for the combination of both larger epoxy and amine was the lowest. These can be explained in terms of their diffusion coefficients. In addition, the size effect on the reaction kinetics was more striking for epoxy than amine in the curing process. This was because epoxy reacted only once but amine did twice. When the primary amine reacted with epoxy, the resultant secondary amine was incorporated into the three-dimensional network. Hence, even if the primary amine had a higher mobility, the movement of the part after the reaction slowed down, making the further reaction to be the tertiary amine slow. Finally, it was shown that although the smaller epoxy reacted faster than the larger one in the mixed system of larger/smaller epoxy and amine, there was no difference in the reaction progress depending on the molecular size of amine.