A sustainable pore wall strengthening for strong and fire-retardant nanopolymerised wood

Cellulose aerogels prepared by the directional freezing method show huge potential in the field of thermal insulation materials, tissue engineering, and building blocks. However, poor mechanical strength and fire resistance limit their application in buildings and engineering. Inspired by the chemical crosslinking of wood cell walls, we propose a sustainable wall-strengthening strategy for robust cellulose aerogels with high mechanical strength, superior thermal insulation, and flame-retardant performance, denoted as nanopolymerised wood. Specifically, oriented cellulose aerogel, prepared from cellulose nanofibers and polyvinyl alcohol, is impregnated with Na2SiO3 solution and then thermally crosslinked to obtain nanopolymerised wood. The cellulose nanofibers served as a supporting skeleton, while polyvinyl alcohol and Na2SiO3 acted as fillers and adhesives, respectively. This combination densifies the pore walls, resulting in an enhanced compressive strength of the nanopolymerised wood to 64.2 MPa. The directional channels with high interfacial thermal resistance lead to a low radial thermal conductivity of 0.027 W·m−1·K−1. Furthermore, the covalently crosslinked silicates provide nanopolymerised wood with outstanding fire-retardant and self-extinguished properties. The biodegradable components, good mechanical properties, superior thermal insulation, and fire-retardant performance of nanopolymerised wood make it a promising material for sustainable buildings and machine envelopes.