Facile synthesis of novel reactive phosphoramidate siloxane and application to flame retardant cellulose fabrics

A novel reactive phosphoramidate siloxane (DTSP) containing silica, phosphorus and nitrogen was successfully synthesized by the Atherton–Todd reaction and characterized by FT-IR and NMR. DTSP was bound onto cotton fabrics through the sol–gel method to improve flame retardancy. The combustion and thermal degradation properties of cotton fabrics before and after treatment were investigated with tests based on limiting oxygen index (LOI), vertical flammability, cone calorimetry and by thermogravimetric analysis. The phosphoramidate siloxane compound can significantly improve the flame retardant properties of cotton fabrics by promotion of char layer formation and release of noncombustible volatiles. The LOI of cotton with 16% of weight gain can reach 30.3%, which is significantly higher than control cotton and 27.0% of LOI value can be maintained after 20 washing cycles. In addition, this finishing method caused a slight decrease of tensile strength and breaking elongation for cotton fabrics, which suggests that this kind of flame retardant material has a certain potential in practical applications.