High‐Performance Lyocell Fiber– PLA Continuous Filaments for Green 3D Printing via Coaxial Extrusion Technology

ABSTRACT Continuous natural fibers exhibit poor precision, strength, and printability in prepreg filaments due to their uneven fiber diameters and weak interface bonding with resin matrices, limiting their application in continuous fiber 3D printing. To overcome these challenges, this study exploits the excellent diameter uniformity of lyocell (LC) fibers to develop a high‐performance, predominantly bio‐based LC–polylactic acid (PLA) pre‐impregnated composite filament for continuous fiber 3D printing. Furthermore, we propose a simple, industrially scalable “one‐step chemical impregnation coaxial extrusion” process using diphenylmethane diisocyanate (MDI) to establish a robust fiber–matrix interface. The interfacially modified LC fiber–PLA continuous filament (LPF) with 23.2% fiber content achieved a tensile strength of 193.7 MPa and an elastic modulus of 6.9 GPa, representing 4.0 times and 4.3 times higher than pure PLA, respectively. Furthermore, LPF exhibits excellent printability, with continuous fiber 3D‐printed specimens achieving a tensile strength of 123.2 MPa. Notably, MDI treatment successfully established covalent bonds between LC and PLA, enhancing interfacial bonding strength by 107% and forming a smooth modulus gradient that facilitates efficient stress transfer. This work provides a simple, efficient, and industrially viable strategy for fabricating prepreg composite filaments, opening new possibilities for high‐performance green continuous fiber 3D printing.