On the compatibility of lignin derivatives in polylactic acid composites and their 3D printability

Additive manufacturing, or 3D printing, provides customized solutions for various applications and thus revolutionizes industries. Polylactic acid (PLA) is an important feedstock for fused filament fabrication, but its costly production limits its use. Lignin, the most abundant naturally available aromatic polymer, shows potential as a filler in biocomposites with PLA. However, the two typically exhibit poor compatibility. Chemical modification of lignin can improve this compatibility. In this work, birch alkaline lignin was ethylated and acetylated in different ways to better understand their performance in thermoplastic PLA formulations. To maximize miscibility between the two, a solvent-casting approach was adopted before processing and extrusion into thermoplastic composites. The lignin-PLA compatibility was assessed by studying their morphology, tensile properties, thermal properties, and viscoelastic properties. It was found that ethylated lignin, modified with less harmful chemicals, improved the tensile strain and toughness of PLA composites, while the viscoelastic properties and T g indicate improved compatibility when acetylated lignin was used. In addition, all composites were successfully 3D-printed using fused filament fabrication, with lignin content up to 20%. This work shows the potential of using lignin and lignin derivatives in PLA composites toward more sustainable materials.