Fire resistance of wood treated with various ionic liquids (ILs)

Ionic liquids (ILs) have been investigated for their potential as reagents for enhancing the fire resistance of wood. The following ILs were in focus: 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1-ethyl-3-methylimidazolium hexafluorophosphate ([C2mim][PF6]). Supposedly, these ILs do not dissolve or degrade wood components to a large extent. No morphologic changes were observed in any IL-treated wood samples, but they showed an enhanced fire resistance compared with that of untreated wood. Scanning electron microscopy and energy-dispersive X-ray analysis demonstrated that the ILs are penetrated into the cell walls. The wood treated with [C2mim][PF6] exhibited the highest fire resistance based on thermogravimetric and differential thermal analyzer studies: it was more resistant against flaming at approximately 350 degrees C and the subsequent glowing at higher temperatures. This enhanced fire resistance was interpreted by dehydration in the presence of the ILs under observation. In general, ILs are promising reagents for improving the thermal properties of wood.