Carbon nanotube nano-bridging unlocks high-performance epoxy composites reinforced with unidirectional alkali-treated ramie fibers

The increasing interest in reducing the dependence on fully synthetic reinforcement materials in engineering applications has encouraged the development of natural fiber-reinforced composite systems. This study investigates the effects of alkali treatment of ramie fibers and the addition of carbon nanotubes (CNTs) on the structural integrity and mechanical behavior of epoxy-based unidirectional (UD) ramie fiber hybrid composites. The composites were fabricated via a vacuum-assisted resin infusion process, incorporating different CNT contents of 0.1, 0.3, 0.5, and 1.5 wt%. The results showed that alkali treatment improved the interfacial bonding between ramie fibers and the epoxy matrix, thereby enhancing tensile and flexural properties. The incorporation of CNTs further improved the mechanical performance of the composites, with the optimum properties achieved at 0.5 wt% CNT content. At this concentration, significant improvements were observed in tensile, flexural, impact, and interlaminar shear properties, driven by enhanced stress transfer and CNT-induced interfacial nanobridging. However, excessive CNT incorporation reduced the mechanical performance of the composites. Overall, the findings demonstrate the potential of CNT-assisted unidirectional ramie fiber/epoxy composites for lightweight and structural applications.