Model-free cure kinetics of tetra-functional epoxy reinforced with GO and p-Phenylenediamine modified GO

Abstract

Tetra-functional epoxy was reinforced with graphene oxide (GO) and p-Phenylenediamine functionalized graphene oxide (fGO). FTIR and XPS analysis of fGO confirmed the attachment of amine groups on its surface. Data obtained from nonisothermal DSC scans of neat epoxy and epoxy modified with 0.1 and 0.5 wt.% GO and fGO was studied to evaluate the effect of filler content and chemistry on the curing behavior of epoxy. Cure analysis was performed quantitatively using the integral isoconversional method to identify the dependence of activation energy (Eα) on conversion. Eα for neat epoxy increased with increase in conversion, possibly because at higher conversions, reactions such as etherification and homo-polymerization controlled the reaction kinetics. The addition of GO and fGO both displayed a lower activation energy in the conversion range α = 0.5−0.9 as compared to neat epoxy. The activation energy of fGO reinforced epoxy remained almost constant with change in conversion. This behavior was attributable to the amine groups attached to the surface of the filler, which acted as a secondary hardener and triggered the epoxide ring opening reaction. This fact was supported by the comparative XPS analysis of fGO and curing agent which clearly indicated the compositional similarities between the two. Further the autocatalytic model was used to determine reaction parameters. The overall order of the curing reaction was more than unity throughout, indicative of a complex reaction mechanism.