A durable flame retardant system of phosphate with hydroxyl groups and cross-linking agent for cotton fabrics

Cotton fabrics are highly flammable and cause serious fire hazards. To mitigate fire hazards, the flame retardant DPTE was synthesized from diethylenetriamine pentamethylenephosphoric acid and triethanolamine. DPTE grafted onto cotton fabrics via a novel cross-linking agent DPGE and imparted cotton fabrics with exceptional flame retardancy and high durability. The treated fabrics (FRC30) achieved a limiting oxygen index (LOI) of 37.7 % and showed only 50.0 mm of damage length. Peak heat release rate of FRC30 decreased by 61.53 % to control cotton fabrics (CCF). After 50 intense laundering cycles, the FRC30 still had a LOI of 29.7 % and passed VFT easily. The treated cotton fabric exhibits excellent stability, due to the efficient esterification reaction between compounds containing polyphosphate groups and polyols, as well as the stable C–O–C covalent bonds. Thermogravimetric-Fourier Transform Infrared (TG-FTIR) spectroscopy showed that decomposition of FRC30 started earlier, and the volatile combustible gases were drastically reduced. After VFT burning, the char residue of FRC retained the intact structure of cotton fabric, confirming the condensed-phase flame retardant mechanism. Moreover, the tensile strength (weft) increased by 20.10 % and the air permeability increased by 78.31 % due to the grafting of the cross-linking agent. Using dicyandiamide to promote efficient esterification between compounds containing phosphate groups and polyols, and grafting the resulting esters onto cellulose via C–O–C covalent bonds through a crosslinking agent, was an effective technique to get durable, formaldehyde-free flame-retardant cotton fabrics.