A mechanistic approach on the curing kinetics of benzoxazine-filled oxygen plasma treated graphene nanosheets

The present study aims to improve the understanding of the role of plasma treated graphene nanosheets on the curing characteristics of benzoxazine nanocomposites. As-synthesized benzoxazine monomers were well characterized by Nuclear Magnetic Resonance (NMR) as well as Fourier-transform infrared (FT-IR) spectroscopy. Also, the plasma treatment was utilized to alter the surface chemistry of graphene nanosheets (GNSs). Differential Scanning Calorimetry (DSC) revealed that the incorporation of GNSs into benzoxazine resin drastically reduces the curing peak temperature (Tc) and hence the enthalpy of curing reaction (∆H_c) to about 43 °C and 91 J g⁻¹, respectively. It was found that GNSs act differently below and above 1 wt% due to their percolation threshold. The obtained activation energies (E_a) by Kissinger and Ozawa model were lower than those calculated by other researchers yet, not significantly different with each other. Then the iso-conversional model of Freidman showed that E_a of the nanocomposite varies during benzoxazine polymerization and these changes directly attributed to the evolutional rearrangement of polybenzoxazine network in the presence of GNSs and were differentiated by three regions through which the mechanistic interpretations of various phenomena can be highlighted. (paper)