Flame retardancy and mechanism of polymer flame retardant containing P-N bonds for cotton fabrics modified by chemical surface grafting

To improve the flame retardancy of cotton fabrics, a non-halogen and non-formaldehyde polymeric flame retardant (ACAPOC) was synthesized by a solvent-free method. ACAPOC was grafted onto cellulose, and the resulting -N-P(=O)-O-C bonds displayed p-pi conjugation, hydrolysis resistance, and greater stability than P-O-C covalent bonds. A mechanistic study showed that ACAPOC affected the thermal degradation pathway of cotton fabrics, which promoted fibers to dehydrate into carbon by generating phosphoric acid or polymetaphosphoric acid through thermal decomposition, interfering with the combustion process. In addition, the non-combustible gases produced by decomposition also diluted the combustible gases, which comprehensively affected the combustion heat cycle. ACAPOC had unobvious effect on crystal structure and surface morphology of cotton fabrics, but greatly reduced the combustion efficiency. ACAPOC-25% underwent 50 LCs in conformity to AATCC 61-2013 3A standard, which can be considered as durable flame-retardant cotton fabrics. Moreover, damage to physical properties barely affected practical application. Taken as a whole, ACAPOC is a low-cost, easy-to-synthesize and efficient flame retardant for cotton fabrics, which may also be applied to other materials such as synthetic fibers.