Preparation of durable and flame retardant lyocell fibers by a one-pot chemical treatment

Cellulosic fibers are usually finished with flame retardant via repeated pad-dry-cure processes. The present contribution reports a simple, facile, and one-pot chemical treatment process to access durable flame retardant lyocell fibers by directly immersing the fibers into the solution of a flame retardant ester of 2,2-ethanolamine diphosphoric acid (EADP) and urea for a certain time without using catalyst and cross-linker. As demonstrated, the treated lyocell fibers with grafted EADP show excellent flame retardancy and durability, as evidenced by an increase of limiting oxygen index value up to 37.8% and still 25.6% after 40 washing cycles. The key to success is ascribed to the formation of three dimensional flame retardant structures with EADP. Various analytical techniques, including raman spectroscopy, scanning electron microscope, thermogravimetry, and TG-infrared coupled technique prove that the carbonaceous residue and non-combustion gases were preferably generated during thermal decomposition process of treated fibers. Microcombustion calorimetry results revealed a significant reduction in the peak of heat release rate. The results indicate that EADP is potential for using as an efficient durable flame retardant of lyocell fibers.