Interface Interactions between In Situ Mechanically Exfoliated Graphene with Wrinkles and Edge Carboxyl Groups and Natural Rubber: Experimental and Modeling Investigations

Abstract

Enhancing interactions between graphene (GE) reinforcements and the rubber matrix can effectively improve the overall performance of rubber composites. In this work, a new method was developed to prepare in situ mechanically exfoliated graphene (IS-GE) with wrinkles and edge carboxyl groups by ball-milling graphite and natural rubber (NR) powder. Subsequently, IS-GE/carbon black/NR (IS-GE/CB/NR) composites were fabricated via mechanical mixing and vulcanization. The results indicated that the wrinkle degree and the oxygen content of the IS-GE could be controlled by the ball-milling time. The highest mechanical properties and thermal conductivity of the IS-GE/CB/NR composite were achieved by adding 10 phr (parts per hundred rubber) IS-GE that had undergone ball-milling for 24 h. By integrating experimental characterization with molecular dynamics (MD) simulations, this research quantified microstructure–property correlations in the IS-GE/NR composites by taking into account the wrinkles and edge carboxyl groups of the GE. The interfacial interactions between IS-GE and NR increased with an increasing wrinkle degree and edge carboxyl group content. The MD simulations showed that the NR in the IS-GE/NR composite with 8.01% oxygen content from edge carboxyl groups on the IS-GE had the lowest mean square displacement (MSD) and fractional free volume (FFV), which indicated that the IS-GE presented a strong adsorption effect on the NR molecular chains and reduced GE agglomeration. Young’s modulus of the NR composites was significantly enhanced with increasing GE wrinkle degree. This research provides new molecular-level insights into the design of GE/NR composites with high mechanical and thermal properties, as well as low fatigue temperature rise.