Novel Softwood\nLignin Esters as Advanced Filler to\nPLA for 3D Printing

In this study, we explored the selectivity of softwood\nlignin toward\nesterification through chloromethylation. Organosolv pine lignin chloromethylated\nby a novel greener protocol was subjected to esterification with decanoic\nacid (C10), tetradecanoic acid (C14), and stearic acid (C18). The\nsuccess of lignin esterification was confirmed by using FTIR and NMR\nspectroscopy. For composite preparation, modified lignin was incorporated\nwith PLA in varying proportions (10%, 20%, 30%, and 40%) using the\nsolvent casting technique. The thermal and mechanical properties of\nthe solvent-cast films were analyzed. Notably, lignin esters increased\nthe glass transition temperature (<i>T</i><sub>g</sub>)\nof PLA by a few degrees: tetradecanoic acid (C14) at 30% loading exhibited\nincreases <i>T</i><sub>g</sub> from approximately 68 to\n72 °C. Mechanical testing showed that blending PLA with lignin\nand its ester derivatives improves its properties. Pure PLA has moderated\nductility and stress but lowered stress levels compared to PLA-lignin\nester blends. Adding 30% lignin reduced strength and strain, making\nthe material more brittle. In contrast, the PLA + lignin C14 ester\n(30%) blend achieved the highest stress and strain, enhancing toughness\nand strength. This makes lignin C14 ester a promising additive for\nimproving the mechanical properties of PLA in applications requiring\ngreater strength and toughness. The composition with optimum properties\nwas selected for production of the 3D-printing filament. Three extrusion\ntemperatures were evaluated, and the advanced mechanical properties\nof 3D-printed filament along with surface morphology were analyzed.