Porous and hollow bamboo fiber foams with enhanced hydrophobicity and tailored insulating performance

Plant fiber foams are gaining increasing attention as a sustainable alternative to petroleum-based plastic foams, yet their hydrophilicity and mechanical limitations hinder practical application. Herein, bamboo fiber foams with tailored microstructure were constructed. Two distinct types of cellulose nanofibers (CNFs)—high-solid cellulose nanofibers (HS-CNFs) and low-solid cellulose nanofibers (LS-CNFs)—served as key structural regulators. HS-CNFs were prepared via mechano-enzymatic fibrillation, while LS-CNFs were obtained through succinic anhydride esterification. Crucially, these distinct types of CNCs dictated fundamentally different foam architectures. HS-CNFs promoted porous networks, whereas LS-CNFs enabled hollow structure. The addition of 10% SiO 2 aerogel to HS-CNF-reinforced foams significantly enhanced hydrophobicity, whereas incorporating 30% SiO 2 into LS-CNF-reinforced foams provided insufficient improvement. MTMS modification effectively imparted hydrophobicity to all foams regardless of CNF type. The hydrophobic hollow LS-CNF-reinforced foam incorporated with 5% MTMS loading exhibited ultralow thermal conductivity (0.047 W/(m·K)) and a density (0.049 g/cm 3 ). In contrast, hydrophobic porous HS-CNF-reinforced foams demonstrated superior mechanical properties, achieving a compressive modulus of 3.85 MPa and an energy absorption capability of 126.82 kJ/m 3 . This study establishes an eco-friendly CNF-driven strategy for engineering fiber foams with programmable microstructure, enabling multi-functional applications in thermal insulation, packaging scenarios and so on. Graphical