Synthesis of a transparent flame retardant for cotton fabric via a dual functionalization approach

Abstract

The development of transparent and exceptionally effective environmentally friendly flame-retardant textile coatings is of paramount importance. However, there are several barriers, such as changes in colour and long procedural steps for synthesis. We synthesized a novel, highly efficient, phosphorus-based, transparent flame retardant using glycidyltrimethylammonium chloride (G), phosphoric acid (PA) and potassium dihydrogen phosphate (PP). As G is a biodegradable quaternary ammonium salt, it was used as a precursor. Phosphorus was successfully incorporated on G by functionalization and ionic interaction to give G@PA/PP, which exhibited exceptional flame retardant endurance. Cotton treated with G@PA/PP reached a limiting oxygen index (LOI) of up to 45% to obtain high-efficiency flame retardancy and showed excellent results in the vertical flame test (VFT). Furthermore, the G@PA/PP coated cloth withstood more than 900 s of continuous exposure to a flame without burning during the flame test, whereas the control cotton burned away within 16 s. Cone calorimetry confirmed good flame suppression with impressive 84.3% and 90% decreases in peak heat release rate (HRR) and total heat release (THR), respectively. Investigation of the flame retardant mechanism showed that the coating could encourage the formation of regular and dense layers of graphitized carbon in the cotton fibres, thereby preventing the matrix from breaking down into hazardous gases at high temperatures. Further investigation indicated that the cotton treated with G@PA/PP flame retardant acquired efficient flame retardancy, exceptional durability and thermostability. This work presents a straightforward method for developing a novel flame retardant, which is beneficial for overcoming colour change, as the prepared flame retardant is transparent.