Sustainable Development of Multifunctional Jute Fiber-Reinforced Epoxy Composites Enhanced with Agricultural Bran Fillers for Sustainable Structural and Antimicrobial Applications

This study investigates multifunctional jute fiber-reinforced epoxy composites incorporating agricultural bran filler (0–4 wt.%) fabricated by hand lay-up. The composite containing 3 wt.% bran exhibited optimum performance, achieving tensile, flexural, and impact strengths of 76.16 MPa, 81.27 MPa, and 17.19 kJ/m2, respectively. Shore D hardness increased from 58 to 69, while thermal conductivity and coefficient of linear thermal expansion decreased from 0.86 to 0.62 W/mK and 1.16 × 10−5 °C−1 to 0.96 × 10−5 °C−1, respectively. Heat deflection temperature increased from 79°C to 104 °C, while thermogravimetric analysis indicated improved thermal stability and char formation. Under cyclic loading initiated at 70% of the respective ultimate tensile strength, the 3 wt.% composite retained a fatigue strength of 42.86 MPa at 20,000 cycles, 15.4% higher than the unfilled composite. SEM examination of fatigue-fractured specimens revealed matrix cracking, fiber pull-out, fiber fracture, and interfacial debonding, indicating progressive cyclic damage mechanisms. Antibacterial evaluation against Klebsiella pneumoniae showed a concentration-dependent response, with the 3 wt.% bran composite extract producing inhibition zones of 16 mm and 24 mm at extract dosages of 50 μg and 100 μg, respectively. Therefore, 3 wt.% bran provided the most favorable balance of mechanical, fatigue, thermal, and antibacterial properties.