Utilizing Graphene to Enhance Interfacial Bonding Between Carbon Fiber and Polymer Matrix

Identification and analysis of interfacial failure mechanisms are key for any carbon fiber reinforced polymer (CFRP) as propagation of microcracks at the fiber/matrix interface is a common failure mechanism for these composites. In order to unveil these failure mechanisms, mechanical testing and modeling of interfacial interactions must be conducted in a safe, accurate and consistent manner. In this work, a low-cost, graphene-based surface treatment process was developed and analyzed to deposit graphene nanoparticles (GNPs) onto the surface of carbon fibers increasing surface roughness and interfacial properties. The compatibility between this high surface area GNP coating and the commercial sizings typically used in the carbon fiber industry is discussed and evaluated through mechanical testing, finite element analysis (FEA) modeling and surface characterization. The execution of this work is divided into three phases.
The first phase is surface characterization of GNP self-assembly on the carbon fiber surface. Graphene agglomeration is widely accepted to result in depreciation of its benefits in practical applications, and shear mixing, ultrasonication and hydrogen passivation were utilized in this work to produce few-layer GNPs. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize GNPs deposited on the fiber surface.
The second phase of this thesis pertains to single filament pullout testing used to quantify interfacial properties of single carbon filaments embedded in a fiberglass resin system with and without GNP surface treatment and polymeric commercial sizing. After completion of experimental testing, a linear, contact based cohesive zone model (CZM) with applicable traction separation law was developed using the Ansys FEA program to further understand interfacial failure mechanics in this test.
The third phase applies composite four-point bend testing to study the performance of interfacial properties of composite beams made with 50,000 filament carbon fiber tows and the same fiberglass resin system used in single filament testing. Composite testing specimens were manufactured using a wet lay-up process, and load transfer efficiency was quantified using the modified rule of mixtures equation.
Our results demonstrate that the GNP coating was successful in enhancing interfacial properties in single filaments and 50,000 filament carbon fiber tows embedded in a fiberglasss resin system. Furthermore, it was determined that the GNP coating increased interfacial properties in carbon fibers with and without a commercial sizing applied to the fiber surface, illustrating the compatibility between this GNP coating and other polymeric sizings typically used in the carbon fiber industry and opening the door for the next generation of high surface area nanoparticle surface treatment techniques in CFRPs.