Effect of surface modifications on the interfacial properties of luffa fibers for epoxy composites

Purpose The purpose of this study is to investigate the effects of chemical (NaOH) and physical (plasma) surface modifications on the interfacial shear strength (IFSS) and mechanical properties of Luffa cylindrica fiber–reinforced epoxy composites. Design/methodology/approach Luffa cylindrica fibers obtained from Kerman Province, Iran, were treated with 4 Wt.% NaOH solution and low-pressure plasma (argon–oxygen mixture) to improve fiber-matrix adhesion. The fiber diameter, density and tensile properties were measured. The IFSS was assessed using single-fiber pull-out tests. The chemical and structural changes were analyzed using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD). Findings NaOH treatment decreased the fiber diameter and density by removing lignin and hemicellulose, resulting in an enhanced IFSS, but reduced tensile strength and Young’s modulus. Plasma treatment improved the IFSS through surface activation and polar group formation while preserving the structural integrity of the fiber. Both treatments lowered the critical fiber length, with the plasma treatment showing superior adhesion performance. Practical implications The results demonstrate that optimized surface treatments can significantly enhance the performance of Luffa fiber–reinforced epoxy composites, making them suitable for use in lightweight automotive components, eco-friendly construction materials and biodegradable packaging. Originality/value This study provides a novel comparative analysis of the chemical and physical surface modifications of Luffa cylindrica fibers and offers valuable insights for optimizing sustainable fiber reinforcements in epoxy composites. These findings highlight the importance of selecting appropriate surface treatments based on the targeted mechanical properties.