Hydrolysis Residue Lignin from Bioprocessing of Biomass for Functional 3D Printing Filaments

Technical lignin holds promise as a sustainable additive for bioplastics, yet its broad adoption is limited by heterogeneity, sulfur contamination, and the need for chemical modifications or solvent-intensive processing. In this study, we present a simple, solvent-based extraction of low-molecular-weight sulfur-free lignin directly from steam-exploded aspen biorefinery residues. The isolated lignin exhibits a narrow molar mass distribution (Đ = 1.1) and reduced aliphatic hydroxyl content, enabling its direct blending into poly(lactic acid) (PLA) without compatibilizers. When incorporated at 10 wt %, the lignin enhanced the mechanical strength, thermal stability, and ultraviolet (UV) resistance of PLA, while maintaining good interfacial compatibility. This approach yielded an odor-free, lignin-blend suitable for fused deposition modeling (FDM-3D printing). When compared to acetone-soluble hardwood kraft lignin, the properties of the filament are equal or better but without odor and avoiding the costly recovery of lignin from a pulp mill. Overall, the study demonstrates a scalable, low-impact route for valorizing lignin as a functional biopolymer─advancing the circular use of lignocellulosic residues in biorefineries.