Influence of nozzle diameter on mechanical performance and density behavior of wood-reinforced PLA composites fabricated via Fused Filament Fabrication (FFF)

The effect of nozzle diameter on the mechanical and physical properties of wood-filled polylactic acid (PLA) composites produced via Fused Filament Fabrication (FFF) was systematically investigated. Specimens were fabricated using three different nozzle diameters (0.4 mm, 0.6 mm, and 0.8 mm), while all other processing parameters were kept constant to isolate the effect of nozzle diameter. Tensile strength, tensile modulus, elongation at break, flexural strength, flexural modulus, impact strength, and density were evaluated. Increasing nozzle diameter from 0.4 mm to 0.8 mm resulted in increases of 8.9% in tensile strength, 13.2% in flexural strength, and 15.0% in flexural modulus. These improvements were found to be statistically significant (p < 0.05). In contrast, no statistically significant effects were detected on tensile modulus, elongation at break, and impact strength (p > 0.05). Density exhibited a threshold-type behavior, remaining nearly constant between 0.4 mm and 0.6 mm and increasing significantly at 0.8 mm (p < 0.0001). The observed improvements in mechanical performance were considered to be associated with increased extrusion width, enhanced interlayer bonding, reduced void content, and improved internal structural continuity at larger nozzle diameters. Based on the present findings, nozzle diameter was identified as a critical processing parameter for optimizing the mechanical performance of wood-filled PLA composites produced via FFF.