Upcycling of Spent Tea Leaves and Spent Coffee Grounds into Sustainable 3D-Printing Materials: Natural Plasticization and Low-Energy Fabrication

Food processing byproducts are potential filling materials for fabricating sustainable composites with broad applications. We herein report the use of spent coffee grounds (SCG) and spent tea leaves (STL) to prepare biomass/poly(lactic acid) (PLA) composites as novel 3D-printing inks. The results show that the 3D-printability can be upheld at a high biomass loading of 40 wt %. As for strength performance, the biomass addition disrupted the PLA structure and reduced the tensile strength of the 3D-printed specimens. However, elongation at break was enhanced 5-fold at 20 wt % SCG, which could be attributed to the plasticizing effect of the naturally occurring oil in SCG. The SCG oil can be added to STL/PLA for improved ductility. With little oil (<30 mg/g composite) at ∼20 wt % biomass loading, samples prepared from 155 °C-filament showed higher tensile strength than those at 185 °C. Microscopic imaging evidenced more significant pore formation in the latter, rendering the structure delicate. These findings reveal the complex effects of filler properties on the biomass-PLA interface that determines the composite performance.