A novel phosphoramidate and its application on cotton fabrics: Synthesis, flammability and thermal degradation

A novel phosphoramidate named 2,2-dimethyl-1,3-propanediol-N,N-bis(2-hydroxyethyl) (DPDA) was successfully synthesized and used to reduce the flammability of cotton fabrics through flame retardant finishing method. Fourier transform infrared spectroscopy (FTIR), 1H-, and 31P-nuclear magnetic resonance (NMR) were adopted to characterize the chemical structure of DPDA. The flame retardancy and fire behavior of neat and treated cotton fabrics were evaluated by vertical burning, limiting oxygen index (LOI) and cone calorimetric tests. To further investigate the flame retardant action of DPDA for cotton, the char layers of treated and controlled cotton fabrics after combustion were analyzed by scanning electron microscopy coupled with an energy dispersive X-ray spectroscopy (SEM-EDX); then the pyrolysis products released from DPDA and cotton fabric samples were characterized using thermogravimetric analysis coupled with Fourier transform infrared spectrometry (TG-FTIR). The enhanced fire retardancy for cotton fabrics by the introduction of DPDA was mainly due to the phosphorylation which promoted the formation of phosphorus-rich compact char layer and restrained release of flammable gases in the condensed and gaseous phase, respectively.