Supramolecular Scale Hydrophilicity Regulation Enabling Efficient Dewatering and Assembly of Nanocellulose into Dense and Strong Bulk Materials as Sustainable Plastic Substitutes

Abstract Cellulose nanofibers (CNFs) are ideal building blocks for creating lightweight and strong bulk structural materials due to their unique supramolecular structure and exceptional mechanical properties within the crystalline regions. However, assembling CNFs into dense bulk structural materials with customizable shape and functionalities remains a great challenge, hindering their practical applications. Here, the dewatering issue of aqueous CNF dispersions is addressed by regulating supramolecular scale hydrophilicity using lactic acid, combined with hot‐press molding. This approach enables the fabrication of transparent CNF bulk structural materials with a density of up to 1.426 g cm ⁻³ . The mechanical properties, including isotropic in‐plane tensile strength (75.5 ± 4.5 MPa), flexural strength (198 ± 20 MPa), and hardness (≈300 MPa), surpass most engineering plastics. Moreover, unlike conventional CNF based materials, the CNF bulk structural materials exhibit remarkable water stability and flame retardancy. These unique advantages open a new avenue to bottom‐up assembly of CNFs into high‐performance multifunctional eco‐friendly structural materials, dedicating to substitution of plastics and easing the consumption of petrochemical resources.