Optimization of FFF-printed PLA/date palm fiber bio-composites using Box–Behnken design

This study optimized five Fused Filament Fabrication (FFF) parameters affecting the tensile properties of poly(lactic acid)/date palm fiber (PLA/DPF) biocomposites using a five-factor Box–Behnken design. The investigated factors were DPF content (5–25 wt%), infill density (30%–60%), layer thickness (0.2–0.4 mm), printing speed (50–70 mm/s), and nozzle temperature (210°C–230°C). ASTM D638 Type IV specimens were fabricated and tested, and quadratic response-surface models were developed for tensile strength and elastic modulus. The multi-response optimum was obtained at 15 wt% DPF, 60% infill density, a layer thickness of 0.4 mm, a printing speed of 50 mm/s, and a nozzle temperature of 210°C, yielding a tensile strength of 65.1 MPa and an elastic modulus of 3.85 GPa. Fiber content was the dominant factor for both responses ( p < 0.0001). The tensile-strength model was significant ( F = 42.69, p < 0.0001) and yielded R 2 = 0.974, adjusted R 2 = 0.952, and predicted R 2 = 0.901. The elastic-modulus model was also significant ( F = 26.66, p < 0.0001), with R 2 = 0.9604, adjusted R 2 = 0.9243, and predicted R 2 = 0.8440. The lack-of-fit values were not significant for tensile strength ( p = 0.3854) and elastic modulus ( p = 0.3118), supporting the adequacy of the models. Tensile performance depended nonlinearly on DPF loading and decreased at 25 wt%; this decrease was cautiously attributed to agglomeration, porosity, and reduced matrix continuity. These results demonstrate the value of jointly optimizing material composition and FDM parameters for sustainable PLA/DPF components.