Fused Filament Fabrication of Paper Yarn Reinforced <scp>PLA</scp> Composites: Optimization of Printing Parameters and Enhancement of Mechanical Properties via Response Surface Methodology

ABSTRACT Paper yarn is produced by pulping natural plant fibers or regenerated cellulose fibers into paper sheets, which are then precisely slit into strips according to the desired yarn thickness. These strips are either twisted individually or combined with synthetic fibers to form the final yarn. This study evaluates the feasibility of paper yarn as a reinforcing material in 3D printed continuous fiber‐reinforced composites. A Box–Behnken design within the response surface methodology was used to investigate the effects of fused filament fabrication (FFF) parameters—including printing speed, printing temperature, and layer thickness—on the flexural properties of paper yarn/PLA composites. The established quadratic regression model elucidated the interaction mechanisms, enabling the identification of an optimal parameter range for maximizing mechanical performance. Under these optimized printing conditions, the paper yarn/PLA composites were analyzed for crystalline structure, thermal properties, and mechanical performance. The composite fabricated under response surface methodology‐optimized conditions exhibited superior mechanical properties compared to a pure PLA reference printed on a standard FFF 3D printer with a 0.4 mm nozzle, demonstrating a 29% increase in tensile strength, a 22% increase in tensile modulus, and a 19% increase in flexural strength. Thermogravimetric analysis showed that paper yarn incorporation reduced PLA's thermal stability but maintained printing safety. Differential scanning calorimetry and x‐ray diffraction revealed minimal impact on crystallinity. This study confirms the feasibility of FFF technology for fabricating paper yarn/PLA composites, where paper yarn serves as the continuous fiber phase and PLA as the resin matrix. The findings could offer a valuable reference for further functionalization and structural development.