From Growing Conditions to Composite Performance: Acid‐Engineered Algerian Sisal Fibers for Sustainable Bio‐Epoxy Composites

ABSTRACT In pursuit of sustainable and high‐performance materials, this work investigates the potential of Algerian sisal fibers as renewable reinforcements in bio‐epoxy composites. It is proposed that controlled sulfuric acid treatments can alter the fibers' chemical composition and supramolecular structure, thereby enhancing interfacial adhesion and mechanical performance in the resulting composites. Untreated and sulfuric acid‐treated fibers (2, 5, and 8 wt%) were characterized for cellulose, hemicellulose, and lignin contents, crystallinity index, and surface morphology using X‐ray diffraction and scanning electron microscopy. The 5% sulfuric acid treatment gave the best outcome, increasing crystallinity and reducing surface impurities without introducing micro‐cracks. Before composite fabrication, tensile tests on the fibers revealed that untreated sisal exhibited 226.5 MPa and 6.1 GPa for tensile strength and Young's modulus, respectively. The 5% sulfuric acid‐treated fibers reached 421.9 MPa for strength (+86%) and 13.1 GPa for modulus (+115%). Fibers were then incorporated at 10 wt% into a bio‐epoxy matrix to make specimens for tensile, flexural, and Charpy impact tests. The composites reinforced with 5 wt% treated fibers exhibited superior mechanical properties, including higher tensile strength (67.3 MPa, +86%), Young's modulus (2.2 GPa, +115%), flexural strength (109.3 MPa, +156%), and impact resistance (7.6 kJ·m ⁻² , +138%) relative to neat bio‐epoxy. Scanning electron microscopy analysis of fracture surfaces of the composites after impact testing indicated fiber‐matrix cohesion, which would enhance load transfer and give a more homogeneous stress distribution.