Ambient-dried micro/nanofibrous cellulose composite aerogels with enhanced mechanical strength, thermal insulation and flame retardancy inspired by plant cell wall

Cellulose aerogels (CAs) are considered sustainable thermal insulation materials. However, their preparation is hindered by harsh dissolution conditions of cellulose, the reliance on specialized drying equipment and challenges in scalable production. The flammability of cellulose and the mechanical and thermal insulation properties of CAs still require improvement to cope with complex environments. Inspired by plant cell wall, micro/nanofibrous cellulose composite aerogels (CMN) with mechanical robustness, thermal insulation and flame retardancy were fabricated through mixing and dispersion, crosslinking, freeze molding and ambient pressure drying. Mechanical robustness of CMN gel skeleton is benefited from a highly entangled network of cellulose microfibers, dual nano-reinforcing effects of cellulose nanofibers and silica aerogel powder, and chemical/physical crosslinking. Interface assembly of multi-scale materials easily enables CMN to be produced under ambient pressure drying without cellulose dissolution and energy-consuming drying equipment. CMN hydrophobically modified by chemical vapor deposition exhibits low thermal conductivity (0.0381 W·m ⁻¹·K ⁻¹), low shrinkage (8.56%) and high compressive strength of 2.18 MPa at 80% strain while possessing exceptional thermal insulation, flame retardancy (limiting oxygen index of 29.1%) and self-cleaning properties. This work overcomes the limitations of scalable green production and overall deficient performances of CAs, demonstrating practical potential in thermal insulation and protection.