Phosphorus- and nitrogen-doped silica coatings for enhancing the flame retardancy of cotton : synergisms or additive effects?

In the present work, the synergistic or additive effects due to the concurrent presence of phosphorus- and/or nitrogen-based compounds on the flame retardancy of cotton fabrics previously treated by sol-gel processes have been thoroughly investigated. Indeed, although additives containing P and/or N structures have been exploited for imparting fire resistance to cellulosic substrates, the quantification of their synergistic level has not been fully considered. More specifically, the concept of "synergistic effectiveness" has been applied to cotton fabrics treated with a phosphorus-doped silica coating, further doped with a bisphosphonate, melamine or urea. Flammability and cone calorimetry tests have shown that only phosphorus (i.e. bisphosphonate) is able to promote a certain synergism with the sol-gel derived oxide phases in terms of residue, heat release rate and total burning time.