Synergistic effects occurring between water glasses and urea/ammonium dihydrogen phosphate pair for enhancing the flame retardancy of cotton

Cotton fabrics have been treated with two different finishing compositions based on urea (U) and ammonium dihydrogen phosphate (AP) in order to enhance their flame retardancy properties, particularly referring to the resistance to a flame application (namely, Limiting Oxygen Index tests) and to an irradiative heat flux of 35 kW/m² (by cone calorimetry). The collected results have proven a remarkable increase of cotton flame resistance: indeed, the fabrics treated with the high concentrated bath showed a LOI increase of 121 % (from 19 for neat cotton, to 42 %) and did not ignite under 35 kW/m² heat flux. Thermogravimetry coupled with pyrolysis-combustion flow calorimetry has demonstrated efficient features of the proposed flame retardant system as char-promoter for cotton. In order to reduce the amounts of U and AP employed in the selected formulations, the use of water glasses (WG) has been explored. A very low WG amount has proven to be effective in halving U and AP contents, maintaining the same fire performances already provided by the high concentrated finishing bath. Furthermore, WG have turned out to act as synergistic species as demonstrated by evaluating the synergistic effectiveness parameter.