Constructing ultra-lightweight, thermally insulating and intrinsically flame-retardant all-wood aerogels via a...

As a renewable material combining abundant resources and biodegradability, wood has been extensively applied in the manufacturing of green energy storage, high-efficiency thermal insulation protection, and sustainable porous biomimetic materials. Delignified wood aerogels, owing to low density and thermal insulation properties derived from pore structures, represent an ideal candidate for next-generation thermal management materials in green construction. However, the flammability of cellulose frameworks, coupled with the tendency for pore blockage and framework collapse during conventional physical addition or aqueous chemical modification, has constrained the engineering application of such materials. To address this issue, the top-down in situ chemical grafting approach with the use of an anhydrous phosphoric acid system was adopted in this work. We have developed phosphorylated wood aerogels (PW) by using delignified wood as a template through anhydrous phosphorylation. Scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses confirmed that phosphorus-containing groups are covalently bonded to the cellulose framework by in situ esterification with surface hydroxyl functionality to generate a stable P-O-C covalent network. According to thermogravimetric analysis, PW₅ reaches a char yield of 45.38%, and PW shows a great thermal stability. Combustion testing indicates PW₅ exhibits an oxygen index of 30.2% and a peak heat release rate of 89.45 W/g. PW exhibits instantaneous self-extinguishing fire-retardant properties. The study successfully developed an all-wood aerogel, which combines excellent flame retardancy and thermal insulation properties, demonstrating significant potential for applications in fire-retardant building materials and thermal insulation materials.