Tensile and flexural strength enhancement in carbon‐fiber epoxy composites using a novel method of particle type electrophoretic deposition of carboxyl functionalized graphene on carbon fiber

Polymer composites reinforced with carbon fiber (CF) are strong, light weight and corrosion‐resistant, and have a wide range of applications in automobile, sports, aerospace, wind energy etc. but are prone to fail at the interface of epoxy and fiber due to weak interfacial adhesion between the fiber and epoxy. Formation of an interphase region with a continuous gradation of properties between fiber and the epoxy can potentially delay failure. Development of a larger interphase can be facilitated by the inclusion of graphene platelets on carbon fiber surface through various deposition processes. The present investigation utilizes a unique combination of magnesium nitrate hexahydrate and carboxyl graphene (G‐COOH) to create a colloidal solution for the particulate type deposition of G‐COOH onto carbon fibers through electrophoretic deposition (EPD). Four layers of EPD deposited carbon fibers have been used to make the composite using vacuum assisted resin transfer molding technique. Tensile and flexural tests have been conducted on the pristine and 0.45 wt% of G‐COOH deposited carbon fiber (0.45G‐COOH CF) epoxy composite. G‐COOH addition leads to thickening of the interphase which has been confirmed through energy‐dispersive x‐ray spectroscopy line scanning. The tensile and flexural strength properties of the carboxyl graphene deposited composites exhibited an increase of 62% and 12% respectively. These improvements can be ascribed to the deposition of carboxyl graphene particles on the fiber and an enhancement in interphase thickness. Moreover, the addition of G‐COOH in composites resulted in a 38% increase in tensile strain. The interlaminar shear strength (ILSS) and void content measured in 0.45G‐COOH CF have been compared with pristine carbon fiber composite as well as 1.3 wt% of carboxyl graphene (1.3G‐COOH) deposited carbon fiber fabric composite that had a film type morphology of G‐COOH deposition. There is only a slight decrease in ILSS of 0.45G‐COOH carbon fiber composites occurred compared to pristine carbon fiber composites. The film type morphology of carbon fiber composite showed the highest void content and lowest ILSS compared to other composites. The fracture surfaces of the failed composites were thoroughly examined through scanning electron microscope and they showed that the failure mechanisms in both tension and flexural loading were severely affected by the presence of G‐COOH. Highlights Optimization of electrophoretic deposition process