Nanoengineered All-Cellulose Bilayer Barrier Papers for High-Performance and Recyclable Food Packaging

Plastic packaging poses a major environmental challenge, yet most paper-based alternatives rely on unsustainable coatings and additives to achieve barrier and mechanical performance. Here, we introduce an all-cellulose bilayer barrier paper in which cellulose nanofibrils (CNFs) function as a dual-purpose coating and reinforcement. Rather than applying CNFs as a postcoating, we employ a simple filtration process combining pulp fibers and CNFs that induces spontaneous bilayer formation, yielding a dense CNF layer atop a pulp-rich substrate. This design delivers outstanding performance: oil resistance exceeds commercial standards even at 85 °C (KIT Level 12), water contact angle increases by >60°, water absorption is significantly reduced (Cobb₆₀ decreases from 290 to 50 g·m^-2), and thermal stability can hold up to 270 °C. While air permeability decreases to near zero, the material maintains a moderate oxygen transmission rate at 50% relative humidity (97 cc·m^-2·day^-1·atm^-1). Beyond a 200% improvement in mechanical strength and wet strength suitable for food packaging applications, the bilayer structure remains robust under folding and peeling, outperforming commercial papers for hot food, refrigerated meats, and baking. Importantly, the all-cellulose composition enables over 98% fiber recovery by recycling, substantially reducing the carbon footprint relative to commercial food barrier papers with limited recyclability. By combining nanoengineering, high functionality, and circularity, this work establishes a biobased platform for sustainable food packaging with broad societal and environmental impact.