Changes in properties of 3D printing filaments by extruding at different temperatures and lignin contents

Technical lignin can be used as a plasticizer to provide thermal stability to a material and to facilitate thermal processing. To evaluate the effects of organosolv lignin in polylactic acid (PLA) in this study, we analyzed the performance of 3D printing filaments extruded using different lignin contents and process temperatures. Based on the fracture surface of the fabricated filaments, the fine cracks present in the cross section of the filament decreased as the lignin contents in the PLA and the extruding temperature increased from 150°C to 160°C. However, the mechanical properties of the filament were different at 150°C. When extruded at 150°C without additions of lignin, the neat PLA did not melt completely, resulting in a poor strength performance. Additions of lignin with PLA at the same temperature increased the strength of the filaments owing to heterogeneous nucle-ation. However, upon increasing to 155°C and 160°C, neat PLA had more crystalline substances so that lignin and heterogeneous nucleation instead acted as a weak point for the strength performance. As the lignin content increased, the glass transition point (Tg), crystallization temperature (Tcc), and melting point (Tm) decreased for all temperature conditions evaluated. As the amorphous material was mixed with lignin, the thermal properties of the filament were changed by creating heterogeneous nucleation between the lignin and PLA matrix; however, rapid changes in the Tcc were observed at the 150°C extruding temperature. Because of this dramatic thermal fluctuation, more heterogeneous nucleation occurred, causing changes in the mechanical properties of the filament.