Integration of Recycled Thermosets into Reconstituted Porous Scaffolds using Direct Writing with Pickering Foam Inks

The development of sustainable innovations is imperative to improve the recyclability of thermosets, such as polyurethane (PU). In contrast to chemical recycling, physical recycling is a scalable option because of its processability and energy efficiency. Nevertheless, the reconstituted PU offers limited added value, because physical recycling is disadvantageous for structural regulation. We report the feasibility of physical recycling of PU through 3D printing, with the implementation of a Pickering foam ink for direct writing containing recycled PU particles. A basic Pickering wet foam composed of waterborne PU and hydrophobic CaCO₃ nanoparticles is developed and adjusted for structural maintenance during curing. Subsequently, recycled PU particles are incorporated in the foam to formulate a shear-thinning ink for direct writing in ambient conditions. The reconstituted 3D-printed PU scaffold exhibits hierarchical porous structures. The Pickering foaming method can be readily extended to other recycled thermosets. Therefore, the physical recycling, based on Pickering foaming and direct ink writing, fulfills the structural regulation of the recycled thermosets and merges them into reconstituted composite foams with hierarchical porous structures and robustness. This green strategy has the potential to offer a promising approach for the physical recycling of thermosets with sufficient added value in a sustainable manner.