A highly durable reactive flame retardant with –N=P–(N)3– and phosphoric acid ester groups for cotton fabrics

Abstract

A flame retardant hexachlorocyclotriphosphazene (HCCP) diethylenetriamine ammonium phosphoric acid and phosphoric acid ester (HPDPP) with –N=P–(N)₃–, –P(=O)(OCH₃)₂, and reactive –P(=O)(O⁻NH₄⁺)₂ groups was synthesized for cotton fabrics. The results showed that the cotton fabrics treated with HPDPP had high flame retardance and durability. The vertical flammability test (VFT), thermogravimetric (TG) analysis, thermogravimetric-Fourier infrared spectrometer (TG-FTIR) and cone calorimetry tests showed that cotton fabrics treated with HPDPP had high flame resistance, displaying condensed phase flame retardance mechanism. The Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) implied that HPDPP molecular could enter the inner amorphous space and graft on cotton fibers. The mechanical properties of cotton fabrics treated with HPDPP were well sustained. Moreover, the limiting oxygen index (LOI) of cotton fabrics treated with 40% HPDPP reached 41.3%, and after 50 laundering cycles (LCs), it reached 29.7% according to the AATCC 61-2013 3A washing standard (vigorous washing), which suggested the flame retardance and durability of treated cotton fabrics were improved significantly. And the EDS of washed cotton fabrics showed that the cotton fabrics treated with HPDPP combined the lowest metal ions compared with cotton fabrics treated with flame retardants with only reactive ammonium phosphoric acid group, because of the fact that besides the necessary reactive ammonium phosphoric groups, the phosphoric acid ester groups can not combine Ca²⁺ and Mg²⁺ etc. Thus, introducing –N=P–(N)₃– groups and phosphoric acid ester groups is an efficient method to significantly increase the durability of the treated fabrics.

Graphical abstract