Comparing lignin and spent coffee grounds as bio‐fillers in PLA 3D‐printable filaments

Abstract

Material extrusion additive manufacturing is increasingly popular but requires new materials to expand its industrial applicability. This study compares the effects of two bio‐fillers (lignin and spent coffee grounds (SCG)) in a bio‐polymer matrix, polylactic acid (PLA). The bio‐fillers aim to enhance the sustainability of the resulting composites, tune their physical properties (rheology, thermal stability, mechanical resistance and water absorption) and improve 3D‐printability by reducing the temperature at the nozzle. The composite with 15 wt.% SCG exhibited an elongation at break of 22.95% (vs. 8.42% for PLA), a printing temperature of 180°C (vs. 215°C for PLA) and a water absorption after 6 weeks immersion in water of 18.77 wt.% (vs. 5.04 wt.% of PLA), suggesting applications like hydroponic farming. Moreover, small amounts of SCG protected the composite against thermo‐oxidative degradation during extrusion, while lignin enhanced the thermal stability of the composite.Highlights 15 wt.% SCG improved PLA ductility (elongation at break 22.9% vs. PLA's 8.4%). Lower printing temperature (180 vs. 215°C for PLA) was achieved with 15 wt.% SCG. SCG protects composite from thermo‐oxidative degradation. 15 wt.% SCG in PLA absorbs 18.77% water after 6 weeks (vs. 5.04% of PLA). Lignin boosts thermal stability of PLA composite.