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This study explores the use of whey powder in Selective Laser Sintering (SLS) to create porous carbon parts. Whey powder, heated at 150°C, forms solid parts due to melanoidin formation from lactose and whey proteins. Carbonized whey parts maintain their shape with controlled shrinkage, allowing for precise printing with high porosity and mechanical strength. A video demonstrating the process, as well as STL files for printed artifacts, are provided.

Novel customised carbon monoliths with a high specific surface area were synthesised by carbonisation plus activation of dehydrated whey powders, a biomass byproduct of the dairy industry. The whey powders were casted directly by pouring them into a desired mould. After a pseudo-sintering process promoted by the self-reaction of the whey components (mostly lactose and whey proteins) at moderate temperatures (ca. 250 °C), 3D porous carbons were obtained. The process did not require any binder or external overpressure to prepare the 3D porous carbons. Upon thermal activation with CO2 or chemical activation with H3PO4 and KOH, the shape of the monolithic structure was preserved after the development of a microporous network (SBET up to 2400 m2/g). Both thermal and chemical activation had little effect on the macroporosity of the monoliths. Activation of these 3D carbons had to be performed with care to avoid heterogeneous skin/core activation and/or overactivation. Highly porous monoliths (SBET of 980 m2/g; open porosity of 70%) with outstanding compressive strength (10 MPa) could be obtained by thermal activation (CO2) of whey monoliths at 850 °C for 1.5 h. Additionally, the use of whey as a precursor provided the carbon monolith with a relatively high nitrogen content (ca. 3 wt.%).

A novel design of a catalytic stirrer that can only be manufactured by 3D printing techniques is proposed. The stirrer blades are meshed and permeable to fluids. The STL files required for printing these novel stirrers with 2, 3, or 6 blades can be downloaded here. Two groups of STL files are provided depending on the material to be printed, namely PLA or any other selected filament for FDM printing; or whey pastes or any other selected paste for DIW printing. G-code and 3MF files are also provided to print, either by FDM or DIW, stirrers with meshed blades of different infills, namely solid (non-meshed or 100% infill), 50% infill, and 35% infill. The meshed patterns are provided by the PrusaSlicer® Laminator, as detailed in the corresponding publication.

We have designed a lab made extruder for direct ink writing (DIW) to be incorporated into a conventional fused deposition modelling (FDM) 3D printer. The STP and STL files required for printing the different parts of such extruder can be downloaded here. Instructions for their assembly and functioning are detailed in the paper.

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 m2/g) and relatively high compressive strengths (5 MPa).

Whey, the main by-product of the dairy industry, is proposed as a sustainable binder for the production of extruded activated carbon. Coconut shell char was mixed with controlled quantities of either rehydrated whey powders or partially dehydrated liquid whey. After extrusion, extrudates were dried, and carbonised or activated under N2 or CO2 atmosphere, respectively. A comprehensive study of the effect of different parameters including binder proportion, coconut shell char particle size and carbonisation temperature was carried out. The composition of whey prompted Maillard reactions boosted with temperature that conferred a resin-like behaviour to the binder. Quality parameters of the resulting extrudates were their ball-mill hardness, real and bulk densities. All whey-bound pellets retained their original shape after the high temperature treatment. The hardness of those whey extrudates was particularly remarkable considering the biomass origin of this binder. The carbonisation temperature had little effect in the hardness or densities of the carbon pellets. The best pellet formulation comprised the use of coconut shell char powders with particle sizes < 212 µm, in mixtures having a 7/3 char/dry whey mass ratio. The properties of the pellets obtained after the activation of such pellets were comparable to those of commercial activated carbon extrudates. The use of partially dehydrated liquid whey rather than re-hydrated dry whey rendered very similar results. The alkalinity of the binder made the resulting activated carbons adequate for H2S removal at room temperature. An economic estimation of the process placed whey in a practical position within the binder market.

A new porous carbon structures made by sintering whey powder in a mold at 150ºC and subsequent carbonization and/or activation are described. These porous carbon structures represent a step beyond simple activated carbon monoliths, as they can take the shape of any mold and machined if necessary. These carbon materials have a porosity that can reach up 70%, made up of a system of hierarchical and interconnected pores, which gives them a high permeability. Furthermore, they have a much higher mechanical strength than other porous carbon monoliths.

Porous carbon structures derived from whey powders are described and evaluated as potential scaffolds in bone tissue engineering. These materials have a porosity between 48% and 58%, with a hierarchical pore size distribution ranging from 1 to 400 micrometres. Compressive strength and elastic modulus are outstanding for such a porous material, being up to three times better than those of traditional HA or TCP scaffolds with similar porosities. They also present non-cytotoxic and bioactive behavior, due to their carbon-based composition that also includes some residual mineral salts content.