Synthesis of reactive flame retardant containing Si–P–S–N and its application in cotton fabric

In this paper, a flame retardant for cotton fabric containing Si, P, S, and N, namely 6-((2-((triethoxysilyl)ethyl)thio)ethyl)amino) dibenzo [c, e] [1,2] oxaphosphinine 6-oxide (TSTDP), was synthesized by click reaction and Atherton–Todd reaction using cysteamine hydrochloride, triethoxyvinylsilane (VTES) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-pxide (DOPO). The chemical structure of TSTDP was characterized by nuclear magnetic resonance spectroscopy (NMR) and fourier transform infrared spectroscopy (FTIR). Cotton fabric was finished by TSTDP with different concentrations via sol–gel method and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy, and FTIR. The properties of cotton fabric, including limiting oxygen index (LOI), vertical combustion, cone calorimetry, thermal stability, tensile strength, whiteness, and washing stability, were tested. NMR and FTIR analysis confirmed that TSTDP was successfully synthesized. SEM and FTIR analysis indicated that TSTDP was successfully and uniformly loaded on cotton fabric. The flame retardance and thermal stability of cotton fabric treated with TSTDP were greatly improved. The LOI of cotton fabric with 28.8% weight gain could reach 29.9% and still remain at 26.5% after 20 washing cycles. The afterflame time and afterglow time of the cotton fabric finished with the TSTDP concentration of 100 g/L was up to 0 s. TSTDP finished cotton fabric had excellent tensile strength retention and whiteness. The synthesis of TSTDP and its finishing on cotton fabric provided a new perspective for the preparation of flame retardant textiles. Graphical abstract