Additive Manufacturing and Characterization of Continuous Nettle Fiber-Reinforced PLA Composites

Continuous nettle fiber-reinforced PLA composites were fabricated using a custom-designed fused deposition modeling (FDM) 3D printer equipped with an in-nozzle fiber impregnation system. The influence of hatch spacing and layer thickness on fiber volume fraction, tensile strength, and fracture surface morphology was systematically examined. Fiber content increased from 7.94 vol.% to 12.21 vol.% when hatch spacing was reduced from 1.0 mm to 0.6 mm at a constant 0.4 mm layer thickness, and from 12.21 vol.% to 24.43 vol.% when layer thickness was decreased from 0.4 mm to 0.2 mm at a fixed 0.6 mm hatch spacing. When compared to neat PLA, tensile strength was improved by 18.69% for the configuration of 1_04 and 75.83% for the configuration of 06_02. SEM analysis revealed orderly fiber deposition in all samples, with 3D-printing-induced voids and fiber pull-out observed on fracture surfaces. Reduced hatch spacing and layer thickness resulted in denser fiber packing, consistent with mechanical performance trends. The results highlight the strong influence of printing parameters on the microstructural and mechanical behavior of continuous natural fiber composites produced by FDM.