Enhanced mechanical performance of bi-directional woven hemp fiber/epoxy composites via multi-walled carbon nanotube reinforcement

This study aims to optimize multi-walled carbon nanotubes reinforcement in bi-directional woven hemp fiber/epoxy composites and establish a correlation between nanoparticle loading, interfacial behavior, and mechanical-durability performance. The work provides an integrated evaluation of mechanical and moisture absorption characteristics. Composites were fabricated via hand lay-up with multi-walled carbon nanotube loadings of 0.5–1.5 wt.% and characterized using tensile, flexural, hardness, and impact tests, supported by scanning electron microscopy analysis. Density and void fraction analysis revealed that 1 wt.% multi-walled carbon nanotubes achieved optimal densification with minimal porosity due to uniform nanoparticle dispersion and improved fiber–matrix packing. At this loading, tensile strength increased by 37%, flexural strength by 96.5%, flexural modulus by 52%, and impact strength by 28.2%. These improvements are attributed to crack-bridging, efficient stress transfer, and energy dissipation mechanisms. Scanning electron microscopy analysis confirmed cohesive fractures and improved interfacial bonding, whereas higher concentrations exhibited fiber pull-out, delamination, and microvoids. Moisture absorption decreased from 2.2% for the pure composite to 1.45% at 1 wt.% multi-walled carbon nanotubes due to reduced voids and tortuous diffusion pathways. However, higher loading (1.5 wt.%) resulted in agglomeration and performance deterioration. The developed composites demonstrate strong potential for lightweight structural applications in automotive and sustainable engineering sectors.