Optimized <i>Bombax ceiba</i> /jute hybrid epoxy composites for enhanced thermal insulation performance

Abstract The development of sustainable hybrid natural-fiber composites provides a practical way toward lightweight materials with tailored mechanical and thermal performance. In this study, Bombax ceiba (BC)/jute hybrid epoxy composites were fabricated using a stacked preform followed by compression molding, and the effect of fiber blending ratio on mechanical, thermal, and microstructural properties was systematically investigated. Three compositions-40/60, 50/50, and 60/40 BC/jute by weight-were evaluated. Mechanical testing showed that the J50 composite, with a balanced fiber ratio, exhibited superior flexural strength and impact resistance, indicating effective hybrid synergy and improved stress transfer between fibers and the matrix. Thermogravimetric analysis showed that hybrid systems exhibit varying thermal stability, characterized by distinct degradation stages linked to moisture evaporation, cellulose decomposition, and char formation. Steady-state thermal measurements demonstrated a non-linear dependence on fiber ratio; the J50 composite achieved the lowest thermal conductivity (0.044 ± 0.001 85 W · m −1 · K −1 ) and the highest thermal resistance (0.0916 ± 0.001 20 m 2 · K · W −1 ), highlighting its potential for thermal insulation applications. Fractographic analysis using scanning electron microscopy correlated the observed mechanical behavior with fiber pullout, fracture, and interfacial bonding characteristics. Overall, this study demonstrates that the hybridization of BC with jute fibers allows for the development of sustainable epoxy composites exhibiting balanced mechanical integrity and significantly enhanced thermal insulation, making them highly suitable for building envelopes and thermal insulation applications.