Fatigue resistant cellulose aerogels with flame retardancy and hydrophobicity through a cross-scale reinforcement...

Cellulose nanofiber (CNF) aerogels are promising insulating materials but limited by the poor mechanical properties, moisture sensitivity and flammability. Here, a cross-scale synergistic reinforcement strategy is proposed to simultaneously enhance the mechanical fatigue resistance, flame retardancy and hydrophobicity of CNF aerogel by integrating dendritic microfibrillated cellulose (MFC) and silicon‑oxygen network. In this strategy, CNF serves as the skeleton structure, dendritic MFC with micrometer-scale trunk and abundant branched nano-filaments is interpenetrated into CNF skeleton to provide structural support and enhance interfacial interactions; Silicon‑oxygen network is subsequently established by covalent crosslinks between cellulose molecular chains and siloxane. Benefiting from the obtained multilevel structure that facilitates the rapid transfer and dissipation of stress, the resulting composite aerogel (CMS-3) undergoing 70% strain could quickly recover to 98.3% of the original height. Notably, the permanent deformation was only 1.90% and 3.04% after 1000 loading-unloading cycles in the longitudinal and transverse directions, demonstrating excellent fatigue resistance. Due to the encapsulation of the silane network, the aerogel achieved self-extinguishment within 1 s, and had 29.89% reduction in peak heat release rate (pHRR) compared with CNF aerogel. Additionally, CMS-3 exhibited excellent thermal insulation with a low thermal conductivity of 0.036 W·m^-1·K^-1 and stable insulation performance even under 85% relative humidity.