Interfacial engineering of flax/epoxy composites via graphene fiber surface modification: Mechanical enhancement and marine durability

The structural application of flax fiber reinforced epoxy composites is constrained by poor fiber–matrix interfacial bonding and high moisture absorption. This study investigates graphene oxide (GO) fiber surface coating to enhance the mechanical performance, thermal stability, and marine durability, demonstrated from laminate to full-scale structural level. GO was deposited onto flax fibers via a scalable coating process at concentrations of 0.75, 1.5, and 2.5 wt.%. The modified fibers were used to fabricate composite laminates and a full-scale marine hatch demonstrator using vacuum infusion moulding. The results revealed significant improvements in flexural strength and interlaminar shear strength, while a reduction in tensile strength was observed, attributed to fiber surface modification during the coating process. Thermal analysis revealed enhanced thermal stability and rigidity at moderate GO loadings. Water resistance improved significantly, with moisture uptake reduced by approximately 25% at the laminate level and by up to 40% in the hatch demonstrator when 1.5 wt.% GO-coated fibers were employed. The findings demonstrate that controlled GO fiber surface modification is an effective approach for durable natural fiber composites in marine environments.