Phosphorus based flame retardants are considered to be the best for cellulose-based materials such as cotton and wood. A non-toxic naturally occurring substance with high phosphorus content is phytic acid, which is used by plants as the main storage of phosphorus. It is prevalent in grains and seeds, so we eat it every day. Phytic acid and phytate complexes with various common and non-toxic metal ions or ammonia have been studied on cotton and wood in orderto systematically assess their performance as flame retardants and elucidate their mechanismsof action. Simple combustion tests have been used to gain a first overview of the relative performance of the flame retardants depending on which ion is combined with the phytic acid, and in which proportions. Analytical methods such as TGA and calorimetry have been used to investigate the thermal properties and thermal degradation of the samples. Spectroscopic techniques suchas MAS NMR have been used to explain the chemistry behind the thermal degradation mechanisms in molecular detail. The main focus has been on cotton samples, but an efficient methodology to control the humidity of wood samples in lab scale has been developed for future investigations on wood. Phytic acid and its complexes have a flame retarding effect on both cotton and wood. The thermal process is similar on both materials. The mechanism is low-temperature charring giving less combustible degradation products, followed by cooling polymerization of the phosphate groups in the phytic acid, and formation of a second barrier to prevent the mixture of combustible volatiles and oxygen. It is important to have ionizable protons available in the flame retardant to induce the main mechanism of charring. Cone calorimeter tests on cotton samples show that the samples self-extinguish. Sodium phytates have a better performance than calcium phytates, as shown from combustion tests and FIGRA index on cotton samples. Possibly the superior flame retarding effect of sodium compared to the other ions is because ofthe radical quenching ability of alkali metals, but further investigations are needed into thisissue. Some of the results are also available in Bachelor and Master theses, and in a recently accepted paper in Green Materials Special Issue on Sustainable Flame Retardants. The results may be of interest to the scientific community as well as for companies and organizations that work for a fire-safe and sustainable living environment
