Enhancement of 3D printability and mechanical properties of polylactic acid/lignin biocomposites via interface engineering

Very recently, the additive manufacturing of lignin-based composites has shown promising results toward the sustainable development of green materials. However, the high brittleness and poor 3D printability of the composites restrict their printing, caused by lignin's weak compatibility with polymers and its high viscosity. In this study, a high-performance, printable lignin-based polylactic acid (PLA) composite was investigated through copolymerizing 2-ethylhexyl acrylate at the interface. It was shown that 10 wt% modified lignin (e-lignin) composites exhibit significantly enhanced toughness from 1.16 to 3.84 MJ/m³ and also impact energy from 2.12 to 6.36 KJ/m² relative to the pure PLA. The responsible toughening effect was interpreted by plasticization and the bridging effect of e-Lignin. The low melt viscosity of the dispersed e-Lignin phase caused local thermo-rheological relaxation and promotes the mobility of PLA molecular chains, showing desirable melt viscosity for fused deposition modeling 3D printing. Notable that the adhesion strength between deposited layers during additive manufacturing was increased due to high interfacial diffusion of composites, where an approximately 138% improvement of weld energy was achieved in 10 wt% e-lignin composites compared to those of pure PLA. This study shows the great promise to utilize lignin extracted natural materials particularly in additive manufacturing by replacing petroleum-based thermoplastics.