Cure kinetics of epoxy/graphene oxide (GO) nanocomposites: Effect of starch functionalization of GO nanosheets

Graphene oxide (GO) nanoflakes are reactive towards both epoxy resin and amine curing agent, but their inevitable agglomeration worsens resin/hardener/nanoflake interfacial interactions. In this work, starch was used to functionalize GO nanoflakes. Isoconversional cure kinetics of low concentration epoxy/GO and epoxy/starch-functionalized GO (GO-St) nanocomposites was then studied based on nonisothermal differential scanning calorimetry (DSC) analyses to evaluate the effect of starch-aided epoxy/amine/GO curing reactions. Qualitative analysis of epoxy network formation governed by GO and GO-St was done in terms of Cure Index, where Good and Excellent cure were interestingly observed as a result of starch functionalization. Quantitative cure analyses based on integral and differential isoconversional methods were also allowed for understanding conversion-dependent cure kinetics in terms of activation energy (E-alpha) alteration. The activation energy increased for neat epoxy system at later stage of curing reaction. However, an almost constant trend was seen for the activation energy of GO incorporated epoxy nanocomposites. Observation of a decline in E-alpha values for epoxy/GO-St system with respect to epoxy/GO was due to the autocatalytic curing reaction, which was attributed to facile epoxide ring opening by OH groups of starch. A good confidence was observed between calculated and observed calorimetric data.