Compatibility of Kraft Lignin and Phenol-Organosolv Lignin with PLA in 3D Printing and Assessment of Mechanical Recycling

Lignin is an aromatic biomacromolecule with many promising properties that can be beneficial to polymer blends. The main objective of this work was to investigate the processability, compatibility, and recyclability of lignin blends with poly(lactic acid). Two different commercial kraft lignins and a phenolated organosolv lignin were blended with poly(lactic acid) at various weight percentages, targeting high lignin content (30, 50, and 70 wt %). Obtained blends were used in additive manufacturing via fused deposition modeling. All obtained materials were thoroughly characterized by tensile tests, thermogravimetric analysis, differential scanning calorimetry, and 31P NMR. The recyclability of the polymer blend materials was evaluated by re-extruding them up to four times, and their printability was also assessed. The results showed that the material retained its mechanical properties relatively well for up to three cycles after which its tensile strength decreased by 30%. Phenolated organosolv lignin exhibited better printability across a broader range of lignin content compared to kraft lignin analogs while maintaining similar thermal and mechanical properties.