Novel metal/biopolymer composite filaments for extrusion-based additive manufacturing using CuSn10 as example

An innovative, broadly applicable metal/biopolymer composite filament with high metal fill ratio of 65 % for additive manufacturing using material extrusion achieving successfully sintered metal parts has been synthesized. Over the past decade, Material Extrusion (MEX) has gained popularity as a method for additive manufacturing of metal parts, particularly for producing green parts, due to its flexibility and cost-effectiveness. Specifically designed feedstocks for MEX process have to be provided to achieve high quality properties of metal parts. However, the development of composite filaments with required high-volume metal and MEX-compatible binder matrices remained limited. In this study, a metal/biopolymer composite filament is developed based on CuSn10 metal powder at 65 vol% combined with two novel binder matrices: the first consisted of the binders polylactic acid (PLA) and acetyl tributyl citrate (ATBC), while the second combined PLA, butenediol vinyl alcohol copolymer (BVOH), and ATBC as plasticizer. The binder components are biocompatible and environmentally sustainable. The green parts were successfully printed through MEX and then processed via thermal debinding and sintering in an open atmosphere. Both the debinding and sintering processes were successful and environmentally friendly. The filaments and the resulting metal parts were thoroughly characterized. The results revealed that the feedstock was extremely brittle without the plasticizer. Increasing the plasticizer content improved flowability but led to poorer surface roughness of the filament. Incorporating BVOH reduced the surface roughness and decrease viscosity. The optimal binder matrices were identified as PLA with 10 vol% ATBC and PLA/BVOH with 5 vol% ATBC. CuSn10 parts produced from these new filaments show significant improvements in the mechanical properties, relative density and porosity. This study is significant for metal production using MEX, with CuSn10 powder as a model, demonstrating an improved metal powder ratio of 65 vol% and exploring novel bio-based binder matrices that could potentially be applied to other metals as well.