Flame retardant cotton fibers produced using novel synthesized halogen-free phosphoramide nanoparticles

• Synthesis and characterization of five new nanosized phosphoramide compounds.
• Application of the synthesized phosphoramides as flame retardants on cotton fibers.
• The smallest char lengths were obtained using three phosphoramides grafted to the fibers.
• Lower weight losses for the treated cotton fibers were observed in the TGA diagrams.
• High antibacterial activities for all of the phosphoramides and treated cotton fibers.

Flame retardant cotton fibers were successfully produced using five new nanosized phosphoramide compounds synthesized by ultrasonic method. The 1H NMR spectra of compounds 1–3 illustrate 3J(H,H)cis and 3J(H,H)trans corresponding to the splittings of cis and trans protons present in the CHCH2 bond. Comparing the char lengths of cotton fibers treated with phosphoramides 1–5 indicates that the samples with greater degree of grafting (DG) provide smaller char lengths so that the least and the greatest char lengths are observed for the treated fibers with phosphoramides 1 and 5, respectively. The very close DG and char lengths of compounds 1 and 2 can be described based on their chemical structures containing 4-nitroaniline and 4-chloro-3-trifluoromethyl aniline groups that both can release electrons through their resonance effects to their corresponding PN bonds and enhance the PN system synergistic effect. The TGA/DSC analyses on the treated fibers revealed that the maximum weight losses at 800 °C are occurred within the range 43.52% (for fiber treated with 1) to 56.37 (for fiber treated with 5) which are all smaller than that of the raw fiber (56.83%). The in vitro antibacterial activity experiments on phosphoramides 1–5 displayed the greatest and the least antibacterial activities for compounds 2 and 4, respectively. Furthermore, when these phosphoramides are applied on the cotton fibers, they also demonstrate the above order for the antibacterial activities.