Durable flame-retardant finishing of cotton fabric via constructing multiple crosslinked layers

To improve the flame-retardant performance of cotton fabric, multiple crosslinked layers were constructed on cotton fiber surfaces through polymerization of m-phenylenediamine (MPD)/tetrakis hydroxymethyl phosphonium chloride (THPC) and trimesoyl chloride (TMC). The resulting morphology, general properties, flame retardancy, and durability were characterized and analyzed. Cotton fabric alternately finished with MPD-TMC and THPC-TMC displayed greater changes in surface morphology than that finished with single crosslinked products. The former material had the highest weight gain percentage and so possessed significantly higher limiting oxygen index (LOI) value and weaker heat release, accompanied by formation of a more robust carbonaceous layer during micro combustion calorimetry. After alternating finishing with MPD-TMC and THPC-TMC, the cotton fabric exhibited increased flexural rigidity and decreased air permeability, with the change influenced by the number of finishing cycles. Increased finishing cycles also resulted in an increased LOI, up to 33.5% after five cycles. According to micro combustion calorimetry results, heat release was suppressed more effectively as long as the number of finishing cycles reached three, such that finishing with 3 cycles was optimal in this study. Moreover, a fabric with 3 cycles of alternating finishing almost kept its LOI value after washing in disturbed water for 24 h, exhibiting good durability for flame retardancy, which would be beneficial in real applications.