Experimental investigation of polymer composites reinforced with nanocellulose fibers isolated from Eichhornia crassipes stems and Citrus grandis fruit peel biochar

Biocomposite material is recently gaining more prominent attention among research scientist due to their immense contribution on strength, economically viable and environment friendly. This study focuses on developing sustainable composite materials using vinyl ester resin reinforced with alkali-oxalic acid-treated nanocellulose fibers and biochar particles. Nanocellulose fibers were isolated from Eichhornia crassipes stems, and biochar was derived from Citrus grandis fruit peels, both underutilized and renewable resources. The alkali-oxalic acid treatment enhanced interfacial bonding between the fibers and the matrix, improving the mechanical properties of the composites, which makes the novelty to this study. Nanocellulose fibers offer high mechanical strength and effective load transfer, while biochar contributes to thermal stability and wear resistance, making this combination suitable for eco-friendly, high-performance composites. These materials are viable substitutes for synthetic counterparts in industries such as aerospace, automotive, marine and infrastructure. Among the composites, specimen VNB2 (40 vol.% nanocellulose fibers and 3 vol.% biochar) showed superior mechanical performance with a tensile strength of 135 MPa, flexural strength of 180 MPa and impact strength of 4.8 J due to enhanced stress transfer and matrix reinforcement. Specimen VNB3 (40 vol.% nanocellulose fibers and 5 vol.% biochar) exhibited the best wear resistance with a specific wear rate of 0.009 mm³/Nm, the lowest coefficient of friction of 0.26 and the highest thermal stability with a TG% of 94 and a decomposition temperature of 385 °C. SEM analysis confirmed improved fiber–matrix bonding in VNB2 and VNB3, with minor agglomeration observed at higher biochar contents. These findings highlight the composites’ potential as sustainable, high-performance materials.