Effect of silane-treated jute/sisal cellulose reinforcement on the mechanical, tribological, and hydrophobic behavior of polyester composites

Natural fiber–reinforced composites are attracting attention as sustainable alternatives to synthetic materials, but improving their strength, wear resistance, and water stability remains challenging. The present study focuses on developing silane-treated jute–sisal hybrid fiber-reinforced polyester composites enhanced with plant-derived cellulose microfillers to improve their mechanical, tribological, and hydrophobic performance. The main objective was to strengthen fiber–matrix interfacial bonding and enhance overall composite durability by combining hybrid natural fibers with chemical surface modification. The novelty of this work lies in the integration of silane surface treatment with cellulose microfiller reinforcement, which establishes strong Si–O–Si and Si–O–C bonds that improve adhesion, reduce voids, and minimize water diffusion—an approach not widely reported for hybrid natural fiber composites. The composites were fabricated by hand lay-up with cellulose contents of 0–6 wt%, followed by curing at 120 °C. Among all configurations, the G3 composite (4 wt% cellulose) exhibited the highest tensile strength (115.5 MPa), flexural strength (137.2 MPa), interlaminar shear strength (28.8 MPa), and impact energy (5.16 J), showing a 51% improvement over the untreated system. The G4 composite (6 wt% cellulose) demonstrated the lowest wear rate (0.38 mm 3 N -1 m -1 ) and coefficient of friction (0.014), while fracture toughness improved by 340% and energy release rate by 224% compared with neat polyester. Water absorption decreased to 23.2%, indicating enhanced interfacial sealing and moisture resistance. The correlation between fiber hybridization, silane bonding, and filler dispersion confirms a strong synergistic effect. The developed composites offer a sustainable, high-strength, and wear-resistant material suitable for lightweight structural and tribological applications in automotive, aerospace, and defense sectors.