Leaf-Inspired Hierarchical All-Natural Foams with Ultralow Shrinkage, Mechanical Robustness, and Flame Retardancy via Ambient-Pressure Drying

The development of natural polymeric foams to address environmental issues associated with petroleum-derived polymeric foams, including white pollution, microplastic accumulation, and high carbon emissions, has attracted increasing attention. However, natural polymer-based foams are limited by structural instability during drying and insufficient mechanical robustness, while their inherent flammability further restricts practical applications. Herein, inspired by the hierarchical “vein–mesophyll” architecture of plant leaves, we report an all-natural foam fabricated via a scalable ambient-pressure drying (APD) strategy using bamboo fibers (BF), sodium alginate (SA), and montmorillonite (MMT). This system integrates a load-bearing fibrous skeleton (BF), a continuous polymer matrix (SA), and a nanoscale “brick–mortar” reinforcement (MMT) into a cross-scale synergistic architecture, enabling efficient stress redistribution and capillary-force dissipation during drying. Consequently, the foam achieves ultralow shrinkage (5.71%), low density (47.1 mg cm–3), high compressive modulus (13.3 MPa), and low thermal conductivity (0.032 W m–1 K–1). In addition, the synergistic interaction between SA and MMT promotes the formation of a compact and stable char layer, imparting excellent flame retardancy. This processing strategy also endows the material with biodegradability, recyclability, low cost, and a reduced carbon footprint. This work provides a viable pathway and design paradigm toward high-performance and sustainable foam materials.