Molecular-level dispersion of graphene into epoxidized natural rubber: Morphology, interfacial interaction and mechanical reinforcement Xiaodong She a, b , Canzhong He a, b, * , Zheng Peng a, b, * , Lingxue Kong b a Chinese Agricultural Ministry Key Laboratory of Tropical Crop Product Processing, Agricultural Product Processing Research Institute, Chinese Academy of Tropical Agricultural Sciences, Zhanjiang 524001, PR China b Institute for Frontier Materials, Deakin University, Waurn Ponds, Geelong, VIC 3216, Australia article info Article history: Received 23 August 2014 Received in revised form 4 October 2014 Accepted 26 October 2014 Available online 1 November 2014 Keywords: Epoxidized natural rubber Graphene oxide Interfacial interaction abstract The interfacial interaction of composites dominates the properties of polymeric/inorganic nano- composites. Herein, epoxy and hydroxyl groups are introduced into the natural rubber (NR) molecular chains to anchor oxygenous functional groups on the surface of graphene oxide (GO) sheets and therefore enhance the interfacial interaction between GO and rubber. From the morphological obser- vation and interaction analysis, it is found that epoxidized natural rubber (ENR) latex particles are assembled onto the surfaces of GO sheets by employing hydrogen bonding interaction as driving force. This self-assembly depresses restacking and agglomeration of GO sheets and leads to homogenous dispersion of GO within ENR matrix. The formation of hydrogen bonding interface between ENR and GO demonstrates a significant reinforcement for the ENR host. Compared with those of pure ENR, the composite with 0.7 wt% GO loading receives 87% increase in tensile strength and 8.7 fold increase in modulus at 200% elongation after static in-situ vulcanization. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Due to its significant nature of carbonic monolayer in atomic level, graphene with outstanding mechanical, chemical, and elec- tronic properties finds great potential in many applications, such as electrodes [1], photovoltaic devices [2], energy storages [3], flexible electronics [4] and nanocomposites. Perfect graphene is not naturally available and usually devel- oped from a precursor, graphene oxide (GO), by treating graphite flakes with oxidizing agents. After oxidation process, oxygenous functional groups including hydroxyls, epoxides, diols, ketones, and carboxyls are introduced onto the graphite surface [5e7]. These polar groups significantly alter the van der Waals interactions be- tween GO sheets which can therefore be easily exfoliated to monolayer, and then further reduced to graphene with reducing agents [8]. The unique monolayer structure of graphene has been attracting tremendous attention on developing graphene-filled polymer nanocomposites (PGNs) with solution mixing, melt blending and in situ polymerization method [9]. Nevertheless, the manufacturing of PGNs faces a number of challenges in terms of dispersion and interfacial interaction. Solution mixing has been demonstrated to be an effective way to obtain desired dispersion [10e12]. For example, Ozbas et al. [10] prepared natural rubber (NR)/GO nanocomposites using solution mixing technique, where both functionalized gra- phene sheet and NR were well dispersed in tetrahydrofuran (THF) solution. After completely mixed, THF was removed to obtain the composite. Similarly, Huang and co-worker [11,12] successfully prepared few-layer graphene (FG)/thermoplastic polyurethane (TPU) composites with improved mechanical and self-healing properties by solution mixing method. However, the use of large amounts of solvent and the associated environmental pollution poses a persistent problem for the fabrication of composites. In situ polymerization is an efficient method to prepare GNPs, where the monomer is polymerized in the presence of the filler [13e18]. However, a lot of electrical energy is needed to disperse the filler in * Corresponding authors. Chinese Agricultural Ministry Key Laboratory of Trop- ical Crop Product Processing, Agricultural Product Processing Research Institute, Chinese Academy of Tropical Agricultural Sciences, Zhanjiang 524001, PR China. Tel.: þ61 416 462 459. E-mail addresses: hecanzhong088@163.com (C. He), zpengcatas@126.com (Z. Peng). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2014.10.054 0032-3861/© 2014 Elsevier Ltd. All rights reserved. Polymer 55 (2014) 6803e6810