Effect of reduced graphene oxide on vulcanization of polydimethylsiloxane composites

Abstract

AbstractThis research aims to investigate the effect of reduced graphene oxide (rGO) on the kinetics of addition vulcanization in polydimethylsiloxane (PDMS) elastomers. For this purpose, the synthesis of graphene oxide (GO) and silane‐grafted GO followed by chemical reduction of particles was conducted to prepare rGOs with different surface chemistry. Particles were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, x‐ray diffraction, scanning electron microscopy, and energy‐dispersive x‐ray analysis. Composites of PDMS containing these particles were prepared by solution mixing, and vulcanization of composites was investigated using differential scanning calorimetry. Results showed that the rate and degree of vulcanization reaction increase up to a critical concentration of particles and then decrease afterward. This behavior was attributed to the catalytic effect of chemical groups on the surface of rGOs, whereas the reverse behavior above the critical concentration was correlated to the immobilization of trapped rubber in the network of particles. Grafting graphene oxide by a long alkyl‐chain silane covered these chemical groups, suppressed the catalytic effect, improved the dispersion of particles, and shifted the critical concentration lower. The critical concentration was correlated to the electrical percolation threshold of particles and confirmed by the solvent swelling method. It was also shown that rGO can itself act as the catalyst for the vulcanization of PDMS with no need for platinum. As the dynamic‐mechanical‐thermal analysis showed, the PDMS composites containing 0.75 wt% of particles did not vulcanize properly. However, composites containing fewer particles were vulcanized.Highlights Reduced graphene oxide affects additional vulcanization of PDMS. Below a critical loading, rGO accelerates vulcanization by a catalytic effect. Above critical loading, rGO decelerates vulcanization by a networking effect. Surface groups of rGO control catalytic and networking mechanisms. Silane modification of rGO affects interfacial behavior, thus critical loading.