Development of eco friendly hybrid nanocomposites with improved antibacterial and mechanical properties through NaOH treated natural fibers

• NaOH-treated coir and hemp fibers combined with SiO₂ and Al₂O₃ nanofillers significantly enhance mechanical and antibacterial properties in hybrid nanocomposites. • 7.5 wt. % nanofiller addition improves bending strength, hardness, and antibacterial effectiveness, while excess filler (>7.5 wt. %) causes agglomeration, reducing performance. • NaOH treatment increases fiber-matrix bonding, leading to a 16 % improvement in mechanical properties over untreated fibers. • Hybrid nanocomposites exhibit strong antibacterial activity against Staphylococcus aureus, Streptococcus mutans, Escherichia coli , and Klebsiella pneumoniae. • The findings support the development of sustainable, high-performance antibacterial composite materials for diverse applications. Nanoparticles have emerged as effective enhancers of polymer composite properties, particularly in improving mechanical strength and antibacterial resistance. However, challenges remain in optimizing natural fiber–matrix interfacial bonding and filler dispersion, which affect the overall performance of hybrid composites. This study addresses the research gap by combining NaOH-treated coir and hemp fibers with SiO₂ and Al₂O₃ nanofillers to develop eco-friendly hybrid nanocomposites with superior mechanical and antibacterial properties. Natural fibers were alkali-treated with 5 wt. % NaOH for 4 h to enhance fiber–matrix adhesion, while nanoparticles were incorporated at varying loadings (0 to 10 wt. %) into the epoxy matrix. The composites were fabricated using compression molding. Mechanical characterization included flexural testing (ASTM D790 ) and hardness testing (ASTM E10 ), while antibacterial activity was evaluated using the well diffusion method against Staphylococcus aureus, Streptococcus mutans, Escherichia coli , and Klebsiella pneumoniae. The results demonstrated that 7.5 wt. % nanofiller addition yielded maximum performance, with a 240 % increase in flexural modulus and up to 41 % improvement in hardness for NaOH-treated fiber composites. Compared to untreated fibers, alkali-treated fibers showed a 16 % improvement in mechanical properties. Antibacterial testing revealed inhibition zones as high as 18 mm, confirming strong effectiveness against gram-positive and gram-negative bacteria. This study establishes a novel approach to hybrid nanocomposite design by integrating fiber surface treatment and dual nanofiller reinforcement, supporting the development of sustainable materials for protective, structural, and biomedical surface applications.