Effects of Functionalized Graphene Nanoplatelets on the Morphology and Properties of Phenolic Resins

Hindawi Publishing Corporation Journal of Nanomaterials Volume 2016, Article ID 3485167, 7 pages http://dx.doi.org/10.1155/2016/3485167 Research Article Effects of Functionalized Graphene Nanoplatelets on the Morphology and Properties of Phenolic Resins Jing Dai,1 Chao Peng,2 Fuzhong Wang,1 Guangwu Zhang,1 and Zhixiong Huang1 1 Key Laboratory of Advanced Technology for Special Functional Materials of Ministry of Education, Wuhan University of Technology, Wuhan 430070, China 2 Faculty of Engineering, China University of Geosciences, Wuhan 430074, China Correspondence should be addressed to Chao Peng; Received 13 April 2016; Accepted 3 August 2016 Academic Editor: Alessandro Pegoretti Copyright © 2016 Jing Dai et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Graphene nanoplatelets (Gnps) were covalently functionalized by 3-aminopropyltriethoxysilane (KH550) and noncovalently functionalized by Triton X-100, respectively. The morphology and structure of KH550 modified graphene (K-Gnp) and Triton X-100 modified graphene (T-Gnp) were characterized by Fourier transform infrared spectroscopy, scanning electron micrograph, and Raman spectrometer. The influences of K-Gnp and T-Gnp on thermal conductivity, fracture toughness, and thermal stability of the boron phenolic resin (BPR) were investigated. Both covalently functionalized K-Gnp and noncovalently functionalized TGnp not only improve the dispersion of Gnp in the polymer matrix but also increase interfacial bonding strength between the BPR matrix and Gnp, thus leading to the enhanced mechanical property and thermal stability of nanocomposites. Besides this, mechanical property and thermal stability of the BPR containing K-Gnp are superior to those of BPR containing T-Gnp. 1. Introduction Phenolic resin (PR) is usually used as a resin matrix for ablative composites because of its excellent thermal stability, mechanical strength, and dielectric properties [1, 2]. Due to the introduction of boric acid (BA), boron phenolic resin (BPR) possesses enhanced thermal stability, especially the high thermal decomposition temperature and charring yield [3]. BPR and PR are both important resin matrixes of ablation resistant material for thermal protection system (TPS). In order to satisfy the requirements of the ablative materials, most of researchers have focused on incorporating carbon materials into PR. These carbon materials are including carbon nanofibers, carbon nanotubes, and graphite [4–6]. However, there were relatively few reports about the effect of carbon materials on the properties of BPR. In recent years, carbon nanomaterials have attracted considerable attention from many researchers because of the excellent performance, low density, low cost, and a large number of potential applications. Graphene [7–12] has been widely used as an ideal filler for polymers, due to its unique physical property, high specific area, and relatively low price. Many researchers have selected Gnp/graphene as a novel filler for polymer composites. Wang et al. [13] investigated the factors of Gnp sizes and dispersion on the mechanical and thermal properties of epoxy nanocomposites. The result showed that larger nanoplatelets (Gnp-5) not only exhibit greater reinforcement of the composites modulus than Gnp-C750 but also improve thermal conductivity of epoxy more effectively. Chandrasekaran et al. [14] studied the effect of Gnp on the electrical and thermal conductivity, fracture toughness, and storage modulus of the nanocomposite. The results revealed that the Gnp is an effective reinforcement of epoxies for their mechanical properties. Liu et al. [15] investigated the effect of graphene nanosheets on morphology, thermal stability, and flame retardancy of epoxy resin (ER) and found that graphene nanosheets change the decomposition pathway of ER at a high temperature, enhance the thermal stability, and promote the formation of carbon residue. Chatterjee et al. [16] studied the influence of Gnps and carbon nanotubes (CNTs) on the mechanical properties of epoxybased nanocomposites and the results indicated that the 2 nanocomposites containing Gnps have superior tensile and compressive strength compared to nanocomposite containing CNTs. Due to large surface area and strong van der Waals force, graphene tends to form irreversible agglomerates in polymer matrix and uniform dispersion of Gnp in the polymer matrix. In order to ensure a good dispersion of Gnp in the polymer matrix, functionalization process of Gnp is conducted. Two approaches, including covalent functionalization and noncovalent modification with various organic molecules, are usually used for modifying Gnp surface. Covalent functionalization can be achieved by yielding covalent linkages at the Gnp-polymer interface through the reaction between the carboxyl or hydroxyl groups of Gnp surface and surfactants’ groups. Lee et al. [17] prepared silanefunctionalized graphene oxides (Go) with four different selfassembled monolayers and found that functionalized Go can strengthen the interfacial bonding between the carbon fibers and epoxy adhesive. Ma et al. [18] covalently modified graphene platelets by the reaction of the Gnps’ epoxide groups and the end-amine groups of a commercial longchain surfactant and found that the modified Gnps (m-Gnps) increase Young’s modulus, fracture energy release rate, and glass transition temperature of epoxy by 14%, 387%, and 13%, respectively. In addition, noncovalent functionalization can be achieved by polymer wrapping, adsorption of surfactants, or small molecules via p–p stacking interactions. Li et al. [19] noncovalently functionalized graphene with poly(sodium 4-styrenesulfonate) (PSS) and found that functionalization process improves interfacial bonding between matrix and graphene. Teng et al. [20] noncovalently functionalized graphene nanosheets (GNS) by a functional segmented polymer chain (Py-PGMA) and found that thermal conductivity of Py-PGMA–GNS/epoxy composites increases remarkably owing to the well dispersion of GNS and interfacial interaction between GNS and resin. Although polymers modified by Gnp have been investigated by many researchers, the application of Gnp in BPR was rarely reported previously. In this study, Gnp/BPR composite was prepared by adding functionalized Gnp to BPR resin. Firstly, we modified the surface of Gnp to obtain functionalized Gnp by two different approaches. The first one is covalent functionalization method of bonding 3-Triethoxysilylpropylamine (KH550) coupling agent containing epoxy ended groups on the surface of the Gnp. The second one is noncovalent functionalization method of attaching electrostatic repulsion of the hydrophilic group of nonionic organic surfactant Triton X-100 to the surface of Gnp. Then we mixed modified Gnp with BPR res (...truncated)