From whey robocasting to custom 3D porous carbons

Abstract

We describe how robocasting and carbonisation of partially dehydrated whey, a surplus of the dairy industry, produced 3D porous carbons with custom morphologies. A relatively simple printing device was first used to manufacture 3D structures of whey pastes. The whey pastes behaved as a thermoset polymer when heated hence keeping the original shape of the printed pieces upon carbonisation, albeit an isotropic size reduction (23%) due to thermal shrinkage. The rheological properties of the whey pastes were similar to those of other inks commonly used in direct ink writing, with a shear thinning behaviour and static and dynamic yield stresses that predicted their printability in most robocasting devices. Once the 3D whey structures were printed, a heat-curing process was required to avoid the uncontrolled emission of volatiles that would otherwise distort them. When doing so, 3D lattices of carbon filaments with ca. 500 µm in diameter and ca. 425 µm mesh size were manufactured. The ash content of the carbonised structures, which is related to the salt content of the original whey, was reduced by conventional washing procedures, bringing about 3D hierarchical porous carbons (70% porosity) with modest specific surface areas (500 m 2 /g) and relatively high compressive strengths (5 MPa). • Whey/water pastes can be printed using 3D extrusion printers. • Carbonisation of printed pieces preserves their shape (albeit thermal shrinkage). • 3D carbon pieces combine good mechanical properties and high porosities.