A printed, recyclable, ultra-strong, and ultra-tough graphite structural material

The high mechanical performance of common structural materials (e.g., metals, alloys, and ceramics) originates from strong primary bonds (i.e., metallic, covalent, ionic) between constituent atoms. However, the large formation energy of primary bonds requires high temperatures in order to process these materials, resulting in significant manufacturing costs and a substantial environmental footprint. In this work, we report a strategy to leverage secondary bonds (e.g., hydrogen bonds) to produce a high-performance and low-cost material that outperforms most existing structural compounds. By dispersing graphite flakes and nanofibrillated cellulose (NFC) in water at room temperature to form a stable and homogeneous solution with a high solid concentration (20 wt%), we demonstrate this slurry can be scalably printed to manufacture a graphite-NFC composite that exhibits a high tensile strength (up to 1.0 GPa) and toughness (up to 30.0 MJ/m3). The low density of graphite and cellulose leads to a specific strength of the composite (794 MPa/(g cm-3)) that is significantly greater than most engineering materials (e.g., steels, aluminum, and titanium alloys). We demonstrate how hydrogen bonds between the graphite flakes and NFC play a pivotal role in the superb mechanical performance of the composite, also enabling this low-cost material to be recyclable for an environmentally sustainable solution to high performance structural materials.