Development and Characterization of Jute Fiber–Reinforced Unsaturated Polyester Composites: Effect of Biochar Derived From Textile Sludge

Biochar was synthesized from textile industry solid effluents (sludge) via pyrolysis and incorporated as a sustainable submicron filler (median ∼262 nm) into 1 × 1 plain weave jute–reinforced polyester composites at loadings of 0.00–1.00 wt.% using compression molding. Microstructure was characterized by FTIR and FESEM‐EDS, while mechanical properties were assessed via tensile, three‐point flexural, and Barcol hardness tests. Optimal reinforcement occurred at 0.50 wt.% biochar, delivering peak tensile strength of 29.22 ± 1.22 MPa (+5.2% vs. control 27.77 ± 2.84 MPa), tensile modulus of 2543.58 ± 57.44 MPa (+2.4% vs. 2483.18 ± 187.94 MPa), and flexural strength of 56.83 ± 4.23 MPa (+9.5% vs. 51.89 ± 1.55 MPa). Barcol hardness increased modestly from 96.33 ± 0.58 (unfilled) to 97.67 ± 0.58 at 0.75–1.00 wt.%. Beyond 0.50 wt.%, microstructural analysis revealed biochar agglomeration, leading to stress concentrations, microvoids, and reduced tensile and flexural properties. These findings demonstrate that low‐level biochar incorporation enhances matrix–filler interactions, load transfer, and overall mechanical performance in an eco‐friendly, low‐cost manner. The resulting composites offer a promising sustainable alternative for lightweight structural components, packaging, and automotive interiors, balancing strength, cost‐effectiveness, and environmental benefits. Future work should explore dispersion aids, hybrid fillers, or optimized processing to mitigate agglomeration at higher loadings and further improve properties.