Optimized Mechanical Performance of Carbon Fiber-Epoxy Composite Using Amino-Functionalized Graphene Nanoplatelets
Authors: Hossain Mohammad K. , Chowdhury Md Mahmudur R. , Bolden Nydeia W. 
Published: March 2016

A systematic study has been conducted on processing and characterizing of carbon fiber reinforced epoxy polymer (CFRP) composites to enhance their properties through the optimization of graphene nanoplatelet (GNP). GNP having a two dimensional structure is composed of several layers of graphite nanocrystals stacked together. GNP is expected to provide better reinforcing effect in polymer matrix composites as a nanofiller along with greatly improved mechanical and thermal properties due to its planar structure and ultrahigh aspect ratio. GNP is also considered to be the novel nanofiller due to its exceptional functionalities, high mechanical strength, chemical stability, abundance in nature, and cost effectiveness. Moreover, it possesses an extremely high-specific surface area which carries a high level of transferring stress across the interface and provides higher reinforcement than carbon nanotubes (CNT) in polymer composites. Hence, this extensive research has been focused on the reinforcing effect of amino-functionalized GNP on mechanical properties of carbon fiber reinforced epoxy composites. Amine functionalized GNP was integrated in EPON 828 at different loadings, including 0.1, 0.2, 0.3, 0.4, and 0.5 wt%, as a reinforcing agent. GNP was infused into Epon 828 resin using a high intensity ultrasonic processor followed by a three roll milling for better dispersion. Epikure 3223 curing agent was then added to the modified resin and mixed using a high-speed mechanical stirrer. The mixture was then placed in a vacuum oven at 40 °C for 10 min to ensure the complete removal of entrapped bubbles and thus reduce the chance of void formation. Finally, both conventional and nanophased carbon fiber reinforced epoxy polymer (CFRP) composites were fabricated by employing a combination of hand lay-up and compression hot press techniques. Carbon woven fabrics were properly stacked into eleven layers while maintaining their parallel orientation. Modified epoxy resin was smeared uniformly on each fabric layer using a brush and a wooden roller. The fabric stack was then wrapped with a bleeder cloth and a nonporous Teflon cloth and placed on the plates of the hot press where pressure and temperature were controlled precisely to ascertain maximum wetting of fibers with matrix and compaction of the layup as well as curing. Temperature was kept at 60 °C for 1 hour to attain enough flow of resin at lower viscosity as compared to room temperature and at the same time not to let it flow out of the layup. Temperature was then increased to 100 °C and maintained for 1 hour to obtain completely cured carbon-epoxy composites. After completion of the curing cycles, the laminate was allowed to cool down slowly to avoid any unwanted shrinkage. The conventional CFRP composite were fabricated in a similar fashion. Mechanical properties were determined through flexure and tensile tests according to ASTM standards. In all cases, 0.4 wt% GNP infused epoxy nanocomposite exhibited the best properties. The 0.4 wt% GNP modified carbon fiber/epoxy composites exhibited 19% improvement in the flexure strength and 15% improvement in the flexure modulus. Tensile test results of CFRP composites showed a maximum improvement in the tensile strength and tensile modulus by about 18% and 19%, respectively, for the 0.4 wt% GNP-infused samples over the control sample. Both flexural and tensile properties were observed to reach the highest at the 0.4 wt% loading due to the better interfacial interaction and effective load transfer between the NH2-GNP and the epoxy resin. Furthermore, morphological analysis ensured better dispersion and improved interfacial adhesion between the matrix and the fiber for GNP reinforced composites.