Preparation, printability, and dimensional accuracy of PLA–silk composite filaments for fused deposition modeling: effects of reinforcement content and printing parameters

The incorporation of emerging natural fibers into polylactic acid (PLA)-based biocomposite filaments presents several challenges, particularly in optimising extrusion parameters, maintaining a uniform filament diameter suitable for fused deposition modeling (FDM), and achieving high dimensional accuracy (DA) in printed parts. This study investigated silk fiber as a natural reinforcement for developing PLA-based biocomposite filaments for FDM applications. Suitable extrusion parameters were established and experimentally validated. Filaments with a nominal diameter of 1.75 mm were successfully extruded at silk fiber reinforcement (SFR) contents of 1, 3, and 5 wt.%. These filaments were subsequently used to fabricate tensile specimens based on the nominal Type I geometry specified in ASTM D638, followed by dimensional evaluation. The average filament diameter accuracies were 99.67%, 99.59%, and 99.17% for the 1, 3, and 5 wt.% SFR compositions, respectively. These values describe closeness to the nominal diameter; compliance with the specified diameter tolerance requires a separate assessment. Dimensional analysis of the printed specimens showed high DA for the 1 and 3 wt.% SFR compositions, whereas greater deviations were observed at 5 wt.% SFR. The Taguchi method and analysis of variance (ANOVA) were used to evaluate the effects of SFR content, infill pattern (IP), infill density (ID), and raster angle (RA) on specimen DA. Main effects plots for the signal-to-noise (SN) ratio and mean responses identified SFR content as the most influential factor affecting DA. Overall, the findings demonstrate the feasibility of incorporating silk fiber into PLA filaments for FDM and support further investigation of these biocomposites for engineering applications and sustainable additive manufacturing.