Fire and termite resistance of wood treated with PF₆-based ionic liquids

Six PF₆-based ionic liquids (ILs) were investigated to evaluate their potential as chemicals for enhancing fire and termite resistance of wood. The ILs used in this study included 1-methyl-1-propylpyrrolidinium hexafluorophosphate ([MPPL]PF₆), 1-methyl-1-propylpiperidinium hexafluorophosphate ([MPPR]PF₆), 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIM]PF₆), tetrabutylphosphonium hexafluorophosphate ([TBP]PF₆), trihexyltetradecylphosphonium hexafluorophosphate ([THP]PF₆), and 1-butylpyridinium hexafluorophosphate ([BPYR]PF₆). All of the IL-treated wood samples did not undergo any morphological changes, and exhibited enhanced fire- and termite resistance compared with untreated wood. The fire resistance properties of all of the prepared IL-treated wood specimens were comparable. However, the [EMIM]PF₆- and [THP]PF₆-treated wood showed slightly inferior termite resistance among the tested IL-treated woods. Overall, [TBP]PF₆ was the most promising candidate among the evaluated PF₆-based ILs because it is stable in wood without leaching after water penetration.