The present study investigates a two-stage reinforcement strategy to enhance the tensile performance and reliability of sisal fiber-reinforced bio-based epoxy composites, aligning material development with sustainability-driven design principles. In the first stage, sisal fiber mats were treated with 4 wt% and 5 wt% NaOH to improve fiber-matrix interfacial efficiency, while in the second stage, multi-walled carbon nanotubes (MWCNTs) were incorporated into the epoxy matrix at low weight fractions of 0.15, 0.25, and 0.35 wt% using a combined mechanical stirring and ultrasonication approach. Tensile testing conducted in accordance with ASTM D3039 revealed a systematic increase in ultimate tensile strength (UTS) from 71.24 MPa for untreated composites to 103.32 MPa for 5 wt% NaOH-treated composites, corresponding to an improvement of approximately 45% due to enhanced interfacial bonding. Subsequent CNT modification further improved tensile performance, with an optimum response observed at 0.25 wt% MWCNT, achieving a maximum UTS of 129.36 MPa and an elastic modulus of 8.1 GPa. Regression-based mathematical modelling captured the near-linear strengthening behavior induced by alkali treatment and the non-linear saturation-dominated response associated with CNT addition, with model predictions remaining within experimental scatter. Statistical reliability assessment using Weibull analysis demonstrated reduced strength variability for alkali-treated and optimally CNT-modified composites. Fracture surface analysis using scanning electron microscopy revealed a clear transition from interfacial debonding and fiber pull-out to cohesive fracture, crack bridging, and crack deflection mechanisms at optimized reinforcement levels. This study quantifies the combined effect of alkali treatment and low-loading CNTs on sisal bio-epoxy tensile behavior, achieving ~ 82% strength improvement with an optimum at 0.25 wt% CNT, while enhancing stiffness and maintaining controlled variability within the tested range. By integrating renewable natural fibers, low nanofiller content, and data-driven modelling, this study contributes to sustainable materials innovation (SDG 9), responsible material utilization (SDG 12), and reduced environmental impact through lightweight composite design (SDG 13).
Joshi et al. (Fri,) studied this question.