Enhancing flame retardancy and smoke suppression of wood via in-situ synthesis of amine-phosphotungstic acid nanoparticles with tunable shapes

In this work, we developed a new methodology for generating hybrid wood materials through the in-situ hybridization of phosphotungstic acid (HPW) and organic amines at ambient temperature. By selecting specific molecules of organic amines, this innovative process produces rod-like (imidazole) and spherical (triethylamine) amphiphilic organic-PW nanoparticles (NPs) with tunable particle sizes. The in-situ synthesis of organic-PW NPs within the wood was verified by series of methods for analysis. The resulting wood samples exhibited remarkable flame retardancy and smoke suppression, as demonstrated by successful fulfilment of the UL-94 test, a remarkable 60.1 % reduction in total smoke production, with a weight percent gain of only 7.5 %. Distinct profiles of the pyrolysis products were observed in the organic amine-PW-treated samples compared to pure wood, indicating a shift in the depolymerization pathway from levoglucosenone (LGO) to hydroxymethylfurfural (HMF) in the presence of acid catalyst. Notably, the thermal protection properties of imidazole-PW are higher than those of triethylamine-PW, attributed to the greater stability of cyclic phosphoric acid-imidazole complexes compared to linear phosphoric acid-triethylamine complexes. Our study not only presents an innovative approach to fabricate hybrid wood materials but also demonstrates exceptional flame-retardant and smoke-suppression capabilities, and altered pyrolysis pathways and evaluated intermediate products stability.