Enhanced Properties of Epoxy Composite Reinforced With Amino-Functionalized Graphene Nanoplatelets
Authors: Hossain Mohammad K. , Chowdhury Md Mahmudur R. , Hosur Mahesh , Jeelani Shaik , Bolden Nydeia W. 
Published: March 2016

A systematic study has been conducted on processing and characterization of epoxy polymer composite to enhance its mechanical, viscoelastic, and thermal properties through optimization of graphene nanoplatelets (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 research has been focused on the reinforcing effect of the amine-functionalized GNP on mechanical, viscoelastic, and thermal properties of the epoxy resin-EPON 828 composite. Amine functionalized GNP was infused in EPON 828 at different loadings including 0, 0.1, 0.2, 0.3, 0.4, and 0.5 wt% as a reinforcing agent. GNP was infused into epoxy resin Epon 828 Part-A using a high intensity ultrasonic liquid processor followed by a three roll milling processor for better dispersion. The GNP/epoxy mixture was then mixed with the curing agent Epikure 3223 according to the stoichiometric ratio (Part A: Part B = 12:1). The mixture was then placed in a vacuum oven at 40 °C for 10 m to ensure the complete removal of entrapped bubbles and thus reduce the chance of void formation. The as-prepared resin mixture was then poured in rubber molds to prepare samples for mechanical, viscoelastic, and thermal characterization according to ASTM standards. Molds containing liquid epoxy nanocomposites were then kept in the vacuum oven at room temperature for seven days to confirm full curing of the samples according to the manufacturer’s suggestion. Similarly, neat epoxy samples were fabricated to obtain its baseline properties through mechanical, viscoelastic, and thermal characterization and compare these properties with those of nanophased ones. The reinforcing effect of the amine-functionalized GNP on the epoxy was characterized through mechanical, viscoelastic, and thermal analyses. Fracture morphology of mechanically tested samples was evaluated through scanning electronic microscopy (SEM) study. The mechanical properties were determined through flexure test according to the ASTM standard. Dynamic mechanical analysis (DMA) and thermo-mechanical analysis (TMA) were performed to analyze viscoelastic and thermal performances of the composite. In all cases, the 0.4 wt% GNP infused epoxy nanocomposite exhibited the best properties. The 0.4 wt% GNP-loaded epoxy sample showed 20% and 40% improvement in flexure strength and modulus, respectively. Moreover, 16% improvement in the storage modulus and 37% decrease in the coefficient of thermal expansion were observed due to the integration of GNP reinforcement into the epoxy system. Scanning electronic micrographs exhibited smooth fracture surface for the neat sample, whereas the roughness of surface increased due to the GNP incorporation. This is an indication of change in the crack propagation during loading and a higher energy requirement to fracture the GNP-loaded sample.