Flexible and fire-resistant all-inorganic composite film with high in-plane thermal conductivity.

• HAPNWs were used as flexible matrix to prepare all-inorganic thermal conductive films. • BNNSs were integrated with HAPNWs through facile vacuum-assistant filtration. • The resultant composite films possess good flexibility and fire-resistant ability. • Significant enhancement of in-plane thermal conductivity was achieved. With the enlarging application of thermal conductive composites in aviation field and so on, not only high in-plane thermal conductivity (TC), mechanical flexibility and electrical insulation, but also thermal stability and fire resistance are critically desired. Although with outstanding advantages such as light weight, good flexibility and processability, the intrinsic flammability and high temperature intolerance are Achilles' heel for most polymer-based thermal conductive composites, which severely hinders their application in harsh environments. To solve this issue, we here proposed a facile strategy to prepare flexible all-inorganic composite films inspired by the recent progress of using inorganic nanowires to prepare fire-resistant paper. In this design, one-dimensional hydroxyapatite nanowires (HAPNWs) synthesized via solvothermal method and two-dimensional boron nitride nanosheets (BNNSs) prepared by liquid phase exfoliation were integrated together by vacuum-assisted filtration to form layer-structured composite films, in which HAPNWs provided flexibility and BNNSs offered orientational thermal conductive pathways. When BNNSs loading content was 30 wt%, the in-plane TC value of the resultant composite film reached 6.4 W m−1 K−1 at 25 °C and was still maintained at 5.5 W m−1 K−1 under 100 °C. As expected, the all-inorganic films exhibited excellent flexibility, fire retardant ability and low coefficient of thermal expansion, which show great potential as thermal conductive materials used in harsh environment. [ABSTRACT FROM AUTHOR]