One key challenge preventing effective recycling (e.g., building wastes, e-waste) lies in the gap between the high costs of the recycling process and the limited value of recycled raw materials. While additive manufacturing (AM) has the potential to narrow such a gap by converting waste materials into value-added products through the remanufacturing process, the ink formulation for waste materials remains a formidable task due to poor processibility. In contrast to high-temperature metallurgy (1000~2000 K), a facile approach has been developed to convert waste metals (e.g., stainless steel machining chips) through size engineering into printable and stable inks for 3D-printed electronics at near room temperature. Moreover, the binder chemistry and percolation mechanism were studied, enabling sustainable ink formulation with non-toxic solvents and environmentally benign polymers (i.e., no fluorinated polymer). The ink formulation is generalizable for various functional materials, including other metals, carbons, and clays. As a proof of concept, a 3D-printed strain sensor from recycled SS chips was demonstrated, which was shown to effectively identify even minor strains from the human body, highlighting potential wearable applications.
