Mechanical property optimization of sisal fiber-reinforced PLA composites fabricated by fused deposition modelling using response surface methodology

Fused deposition modelling (FDM) is a widely adopted additive manufacturing technique to fabricate three-dimensional components from thermoplastic feedstock. The investigation is carried out for the effect of layer thickness, nozzle temperature, infill density, and sisal fibre weight fraction on the tensile and flexural properties of sisal fibre-reinforced polylactic acid (PLA) composites fabricated through FDM. A Box-Behnken Design (BBD) within the Response Surface Methodology (RSM) framework was employed to investigate and optimize these four experimental factors. The parameter ranges considered were 0.1–0.3 mm for layer thickness, 190–210°C for nozzle temperature, 60–100% for infill density, and 3–9 wt% for sisal fibre content. ANOVA indicated that fibre weight fraction was the most influential factor for tensile strength, while infill density was the dominant factor affecting flexural strength. The regression models established R 2 values of 98.81% and 92.04% for tensile and flexural strength, respectively. Among the experimental design points, 6 wt% sisal fibre produced the highest tensile strength of 46.50 MPa and flexural strength of 78.38 MPa. The RSM-based multi-response optimization identified an optimum combination of 0.2357 mm layer thickness, 209.61°C nozzle temperature, 78.89% infill density, and 6.41 wt% fibre content, with predicted tensile and flexural strengths of 43.50 MPa and 53.55 MPa, respectively. Confirmatory experiments at the optimized condition yielded tensile and flexural strengths of 40.68 MPa and 50.09 MPa, respectively. The results demonstrate the applicability of RSM for identifying a balanced combination of material composition and FDM processing parameters for sisal fibre-reinforced PLA composites.