Nano-fibrillated cellulose-hydroxyapatite based composite foams with excellent fire resistance.

Thermally insulating materials made from renewable resources are desirable for energy efficient buildings. Traditional petroleum-derived insulating materials such as rigid polyurethane foam and expanded polystyrene display poor flame retardancy and inorganic insulating materials such as silica aerogel are fragile. Herein, we reported a facile approach to prepare cellulose nanofiber (CNF)-hydroxyapatite (HAP) composite foam by a simple freeze-drying process. The resultant HAP-CNF composite foams showed a thermal conductivity in the range of 38.5-39.1 mW/(m K) and very low peak heat release rate (20.4 kW/m2) and total heat release (1.21 MJ/m2). Vertical burning tests also manifested excellent fire resistance and self-extinguishing behaviours. Considering the excellent fire resistance of this composite foam, it is of significance to fire safety solution for buildings insulating materials.