Mechanical properties of polybutadiene reinforced with octadecylamine modified graphene oxide Yan Zhang a , James E. Mark a, * , Yanwu Zhu b , Rodney S. Ruoff c , Dale W. Schaefer d, ** a Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221-0172, USA b Department of Materials Science and Engineering and CAS Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, Hefei, Anhui 230026, China c Department of Mechanical Engineering and The Texas Materials Institute, University of Texas at Austin, Austin, TX 78712-0292, USA d Department of Biomedical, Chemical and Environmental Engineering, College of Engineering and Applied Science, University of Cincinnati, Cincinnati, OH 45221-0012, USA article info Article history: Received 26 June 2014 Received in revised form 18 August 2014 Accepted 24 August 2014 Available online 3 September 2014 Keywords: Polybutadiene Graphene oxide Mechanical property abstract Octadecylamine-modified graphene-oxide (OMGO) polybutadiene nanocomposites with different OMGO loadings were prepared by solution mixing. The dispersion of OMGO in chloroform is greatly improved compared to GO. Toughness and elongation of PBDeOMGO nanocomposites increase by 332% and 191% respectively compared with pure PBD. However, Young's modulus of PBDeOMGO nanocomposite de- creases by 10% at 2-wt% loading. Graphene sheet crumpling accounts for the increased toughness, the absence of modulus reinforcement and the absence of a Payne effect for PBDeOMGO. The oxidation susceptibility of PBD is greatly reduced after the addition of OMGO, which is particularly desirable in the tire industry. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Rubbers (elastomers) are an important class of commercial polymers. Classic elastomers, such as polybutadiene and poly- isoprene are used as general purpose rubbers in high volume products such as tires, hoses, belting, and flexible automotive parts [1]. Rubber materials have been extensively studied because of easy processing, flexibility and excellent thermal properties [2e4]. However, rubber is commonly used in form of composites since pure rubber lacks the required mechanical properties such as wear resistance and strength. Rubber nanocomposites are the class of filled rubbers in which at least one dimension of the fillers is on the nanometer scale. Most commonly used fillers are silica, carbon black, clay and carbon nanotubes [5e7]. Increased modulus is achieved at relative high filler loading such as 20e50 per hundred rubbers (phr), which can reduce toughness due to defects caused by the fillers [8]. However, the incorporation of small-size fillers in cross-linked elastomers results in specific nonlinear mechanical behaviors including Payne effect and Mullins effect. The Payne effect is typically observed at small strain. The dynamic storage modulus decreases strongly with increasing strain amplitude [9]. Mullins et al. first reported that the degree of softening increases with increasing stiffening ability of the fillers [10]. Some Mullins softening is observed in carbon black and silica filled rubber composites systems [11]. Polybutadiene (PBD), a synthetic rubber, has a higher resistance to wear over styrene-butadiene rubber and natural rubber, which are its main competitors in rubber-industry applications due to their lower glass transition temperatures [12]. PBD is a low cost rubber used for soles, gasket, seals and belts [13]. PBD is normally formulated with fillers, such as silica or carbon black. Graphene is an emerging filler candidate that has been widely studied in thermoplastics, but not in elastomers. Graphene shows high thermal conductivity (5000 W m 1 K 1 ) [14e16], highest Young's modulus ever measured (1 TPa) [17] and large theoretical surface area (2675 m 2 g 1 ) [18]. High modulus and large surface area promise dramatic improvement in mechanical properties, which as yet has not been realized. Within the few published paper on elastomers filed with graphene materials, Araby et al. [19] re- ported that tensile strength of styrene butadiene rubber filled with graphene increases by 230% using melt compounding. However, in order to obtain such improvement, a large amount of graphene (24%) was incorporated into rubber, which causes defects in products and increases cost. * Corresponding author. Tel.: þ1 513 556 9292; fax: þ1 513 556 9239. ** Corresponding author. Tel.: þ1 513 556 5431; fax: þ1 206 600 3191. E-mail addresses: markje@ucmail.uc.edu (J.E. Mark), dale.schaefer@uc.edu, schaefdw@ucmail.uc.edu (D.W. Schaefer). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2014.08.065 0032-3861/© 2014 Elsevier Ltd. All rights reserved. Polymer 55 (2014) 5389e5395