Bio-derived bran particle inclusion for tailoring the thermo-mechanical behaviour of Kevlar fiber-reinforced sustainable composites

This research presents a comprehensive evaluation of the thermo-mechanical behavior of Kevlar fiber-reinforced epoxy composites modified with bio-derived bran particle fillers. Composite laminates were fabricated using a hand lay-up technique with a constant Kevlar fiber content (200 g) and bran filler incorporated at varying loadings from 0 to 4 wt% (samples S0-S4). The 3 wt% bran-filled composite (S3) exhibited the most balanced and enhanced performance across all evaluated properties. Tensile strength, flexural strength, and impact energy reached peak values of 161.39 MPa, 172.43 MPa, and 33.94 kJ/m², respectively, while Shore D surface hardness improved to 63. Fatigue testing demonstrated superior cyclic durability for S3, maintaining a stress resistance of 104 MPa after 30,000 cycles. Thermal analysis revealed a significant reduction in thermal conductivity from 0.98 W/mK (S0) to 0.74 W/mK (S3), alongside a decrease in the coefficient of linear thermal expansion from 1.29 × 10⁻⁵ /°C to 1.12 × 10⁻⁵ /°C. The heat deflection temperature increased notably from 91 °C (S0) to 116 °C (S3), indicating improved dimensional stability under thermal stress. Thermogravimetric analysis confirmed enhanced thermal resistance, with S3 showing a delayed onset of decomposition temperature at ~ 357 °C, a DTG peak at 482 °C, and a maximum residual char yield of 23.5% at 700 °C. Scanning electron microscopy of fractured specimens revealed uniform bran dispersion and strong interfacial adhesion in S3, contributing to reduced void formation and improved stress transfer. While water absorption increased with filler content due to the hydrophilic nature of bran, the uptake remained moderate, rising from 0.67% (S0) to 3.84% (S3). Overall, the strategic inclusion of 3 wt% bran filler effectively enhanced the thermal and mechanical performance of Kevlar/epoxy composites, offering a sustainable and high-performance material solution for structural applications operating under thermal and cyclic mechanical loads.