Fabrication and characterization of acacia leucophloea bark fiber-reinforced epoxy composites with lotus seed shell powder as a sustainable bio-filler

• This work examines the production and analysis of Acacia leucophloea (AL) fibers reinforced with epoxy resin and Lotus Seed shell powder (LSSP) as a filler. • FTIR spectroscopy verified the existence of C-H bond vibrations associated with cellulose in AL fiber reinforcement, and XRD shows the crystallinity index of 30.44%. • The optimized composite exhibited increases of 24.47% in tensile strength (TS), 16.33% in flexural strength (FS), 36.52% in impact strength (IS) and 19.23% in Shore D hardness. • Thermal conductivity increased by 27.26%, while the coefficient of linear thermal expansion decreased by 54.12, indicating enhanced thermal stability. • The thermal stability of the composites, varied from 235 to 445°C, indicating a notable enhancement compared to unaltered natural fiber composites. The growing global demand for sustainable materials has driven the shift toward bio-based fiber composites to replace synthetic polymers. However, limited studies have addressed the poor thermal stability and interfacial adhesion of natural fibers, particularly the unexplored Acacia leucophloea bark fiber and Lotus Seed Shell Powder combination. This study develops Acacia leucophloea bark fiber (ALF) reinforced epoxy composites with Lotus Seed Shell Powder (LSSP) as a bio-filler, constant fiber content at 30 wt% and LSSP from 1–3 wt% at an interval of 0.5wt%. The fibers were alkali-treated (5% NaOH, 45 min, room temperature), cut to 20 mm, and dried, while LSSP was mechanically and ultrasonically dispersed in the epoxy prior to hand layup casting. Seven composite specimens were fabricated without and with fiber and differing weight ratios of LSSP filler to evaluate their effects on the mechanical and thermal properties of the composite materials. The integration of LSSP fillers markedly enhanced the mechanical and thermal performance. Compared to the control sample (pure epoxy), the optimized composite (A30L3) exhibited significant improvements with increases of 47.29% in tensile strength (TS), 33.66% in flexural strength (FS), 39.71% in impact strength (IS) and 28.28% in Shore D hardness. Thermal conductivity increased by 30.28%, while the coefficient of linear thermal expansion (CLTE) decreased by 35.49, indicating enhanced thermal stability. The thermal stability of the composites, as determined by thermogravimetric analysis (TGA), varied from 235 to 445°C, indicating a notable enhancement compared to unaltered natural fiber composites. Dynamic mechanical analysis demonstrated the improved viscoelastic properties, signifying superior thermal durability and dimensional stability under dynamic heating conditions. One-way ANOVA and Tukey’s HSD test revealed statistically significant differences (p < 0.0001) across all composite groups. Fourier-transform infrared (FTIR)spectroscopy verified the existence of C-H bond vibrations associated with cellulose in AL fiber reinforcement, and XRD shows the crystallinity index of 30.44%. These composites demonstrated robust antibacterial characteristics, thereby improving functional value. Surface morphological and elemental analysis demonstrated the strong bonding at the interface between AL fibers and the matrix reinforced with LSSP filler, hence reinforcing the structural integrity of the materials. The A30L3 composites consistently exhibited superior mechanical and thermal properties. This work is novel in demonstrating that the combination of ALF and LSSP produces sustainable, multifunctional composites with enhanced mechanical and thermal properties, highlighting their potential for lightweight structural applications.