Interface-engineered modification of fire-safety CNF/MXene composite film with high thermal conductivity and electromagnetic interference shielding

Cellulose nanofibers (CNFs) are characterized by a high aspect ratio and excellent physical and chemical properties, which endow them with significant potential for enhancing functionality when combined with other materials. However, their inherent flammability severely restricts their application in environments exposed to high temperatures or fire risks. To address this issue, the hydrolysis products of (3-aminopropyl)-triethoxysilane (APS) and boric acid react with the hydroxyl groups on the surface of CNF. This reaction forms polyborosiloxane (APS-B)<i>in situ</i>on the surface of CNF, creating a stable polyborosiloxane network. A multifunctional composite film was developed, the introduction of conductive MXene filler yields a multifunctional CNF/APS-B/MX composite film with both electromagnetic shielding and thermal conductivity (TC). Concurrently, the film's exceptional flame retardancy is provided by the APS-B component, which transforms into a dense, glass-like coating upon burning. This layer significantly enhances the thermal stability of the CNF and acts as an effective physical barrier against combustion. The peak heat release rate of the composite film is reduced to 3.4 W g^-1, and the THR is 0.1 KJ g^-1. On this basis, MXene was uniformly dispersed in the CNF dispersion, and the composite film with mussel-inspired structure was prepared by vacuum-assisted suction filtration. A perfect conductive and thermal conductive network was constructed in the plane. The electromagnetic interference SE of the CNF/APS-B/MX composite film reached 34 dB, and the in-plane TC was significantly improved to 9.8 W m^-1K^-1.