Sustainable and Versatile Superhydrophobic Cellulose Nanocrystals

Paper-based materials have been widely used in packaging replacing nonbiodegradable fossil-based polymers due to the increasing concerns on environmental pollution. However, paper is hygroscopic and its mechanical strength is dramatically reduced in the presence of moisture. The current hydrophobic modification of paper via nonbiodegradable polymer coating hinders the recycling of paper. A sustainable approach was proposed to prepare superhydrophobic cellulose nanocrystals (CNCs) by anchoring octadecylamine (ODA) on the surface of CNCs via the self-polymerization of tannic acid and Michael addition/Schiff base reaction between polytannic acid-coated CNCs (PTA@CNCs) and ODA. The obtained ODA–PTA@CNCs could be well dispersed in ethanol and sprayed onto different substrates to form superhydrophobic coatings, such as paper, cotton, and polyurethane. The outstanding superhydrophobicity of ODA–PTA@CNCs is attributed to the low surface energy of ODA and multiscale roughness of CNC nanorods. The promising applications of ODA–PTA@CNCs in waterproof paper-based packaging, antifouling and breathable textile, semipermeable membrane, oil–water separation, Janus paper, and actuators were demonstrated. Furthermore, the durability of superhydrophobic ODA–PTA@CNCs was confirmed by abrasion and washing tests. Overall, ODA–PTA@CNCs are promising sustainable and versatile hydrophobic coatings due to their facile preparation, biodegradability, convenience, and durability.