Sustainable and Robust Coating with Superhydrophobic and Oil-Repellent Performance for Biodegradable Catering Packaging.

Nonbiodegradable functional coatings severely exacerbate the environmental-friendliness of paper packaging. Herein, inspired by the Janus wettability of natural lotus leaves, we demonstrated a practical and easy-to-scale strategy to fabricate a durable, superhydrophobic, oil-repellent, and biodegradable coating for paper-based packaging. A bilayered coating consisting of an inner hydrophilic layer and an outer superhydrophobic layer was constructed on a paper substrate. The hydrophilic layer made of carboxymethyl cellulose sodium formed a hydrated structure by absorbing water from the surroundings, effectively blocking oil penetration. The superhydrophobic layer composed of silica nanoparticles prevented water infiltration. The hydrophilic layer formed strong hydrogen-bonding interactions with the paper substrate and chemically bonded with the superhydrophobic layer, thereby ensuring the firm adhesion of the functional coating to the substrate. The bilayered coating exhibited exceptional superhydrophobicity and oil-resistant property and withstood various treatments, such as bending, scratching, peeling, and aging. Moreover, the coating degraded rapidly and completely in soil. Paper packaging coated with this innovative coating could contain hot water, coffee, milk, oil, oil-water emulsions, and so on. Such an easy-to-scale Janus coating not only achieved robust water-proofing and oil-repellency but also addressed the adhesion between paper substrate and superhydrophobic materials, indicating a practical approach for producing eco-friendly packaging.