Mechanical properties of carbon nanofiber/fiber-reinforced hierarchical polymer composites manufactured with multiscale-reinforcement fabrics

[Display omitted] ► Practical and scalable process to manufacture hierarchical polymer composites. ► Increase in interlaminar shear strength and compressive strength of hierarchical composites. ► Carboxylated-CNFs slide from the matrix whereas amidized-CNFs attach to the matrix. Hierarchical polymer composites – defined as carbon nanofiber/fiber-reinforced polymer composites – were manufactured using multiscale-reinforcement fabrics (MRFs) and they were characterized for their mechanical properties. The MRFs were fabricated by electrophoretic deposition of carboxylic acid- or amine-functionalized carbon nanofibers (CNFs) on the surface of sized or unsized carbon fiber layers. Compared to the base composite (not containing CNFs), the hierarchical composites containing the functionalized CNFs showed an increase in interlaminar shear strength (ILSS) and compressive strength. Panels containing amine-functionalized CNFs had the highest increase in properties: 12% in ILSS and 13% in compressive strength. The reinforcement mechanism was also investigated with emphasis placed on the fiber/matrix interface and the load transfer between matrix, CNFs, and carbon fiber.