Construction of a durable, halogen-free, and phosphorus-free flame retardant cotton fabric system with hydrophobic properties by phase separation and interface polymerization

Inspired by the synthesis of polyurethane, a multifunctional fabric with hydrophobic and long-lasting flame retardancy was prepared through the phase separation and interfacial reaction process between PEI (polyethyleneimine)/BX (borax) aqueous solution and isocyanate terminated polydimethylsiloxane (PDMS-NCO) in tetrahydrofuran solution. The limit oxygen index of the treated fabric increased from 18.0 % to 33.7 %, and the total heat release decreased by 34.2 %. The enhancement of flame retardant performance and thermal stability is attributed to the enhanced char-forming capacity. After 50 cycles of water washing, the cotton fabric can still pass the vertical flammability test because of the curing effect of PDMS-NCO on functional additives. Furthermore, SEM analysis revealed that the formation of nano-rough structures on the fibers was promoted by phase separation, thus leading an increased water contact angle of sample to 139°. The materials utilized in this modified process do not contain elements such as F, Cl, Br, and P, indicating its potential as an environmentally friendly methodology for fabric functionalization.