Characterization of chars obtained from cellulose treated with phosphoramidate flame retardants

Surface chemical investigations of burnt cellulose treated with five different flame retardants based on ethyl ester phosphoramidates have been carried out. Thereby, the elemental composition and structure of the chemical groups present on the char surfaces were assessed via three surface analytical methods, namely X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX) analysis and attenuated total reflectance infrared (ATR-IR) spectroscopy. A portion of the phosphorus is present at the surface as phosphoric acid moieties (more pronounced for less effective flame retardants). In addition, there are indications (from XPS and IR) that the other phosphorus species are chemically bound to the carbon atom of burnt cellulose via a C–O–P bond. Evidence for a condensed phase action of the phosphoramidate flame retardants is found.