Humidity‐adaptive, mechanically robust, and recyclable bioplastic films amplified by nanoconfined assembly

Poly(vinyl alcohol) (PVA) is biodegradable, recyclable, and has high tensile strength. Therefore, it is ideal for the development of environment‐friendly sustainable bioplastics. However, at elevated humidity, the mechanical properties of PVA bioplastic films undergo degradation owing to their intrinsic hydrophilic and hygroscopic nature, hindering their applications. This study proposes a nanoconfined assembly strategy to produce humidity‐adaptive, mechanically robust, and recyclable bioplastic film. The strong hydrogen bonds between PVA and cellulose nanofibrils inhibit the penetration of water molecules into the film to promote humidity resistance. Further, the robust coordination interactions between bentonite nanoplates, PVA, and cellulose nanofibrils restrict the slip of polymer chains during deformation, leading to enhanced mechanical properties. Benefiting from the nanoconfined assembly architecture in aggregated composites, the resulting reinforced PVA film simultaneously exhibits strength, stiffness, toughness, fracture energy, and tearing energy of 55.9 MPa, 1,275.6 MPa, 162.9 MJ m−3, 630.9 kJ m−2, and 465.0 kJ m−2, respectively. Moreover, the film maintains a strength of approximately 48.7 MPa even at 80% relative humidity for 180 days. This efficient design strategy applies to diverse scales and structured cellulose biomacromolecules. Moreover, it facilitates the application of recyclable high‐performance bioplastic films to settings that require high humidity tolerance.