Preparation of Flame Retardant Cotton Fabric Using Environmental Friendly Supercritical Carbon Dioxide

Due to its environmentally benign character, supercritical carbon dioxide (scCO2) is considered in green chemistry, as a substitute for organic solvents in chemical reactions. In this paper, an innovative approach for preparation of flame retardant cotton fabric was obtained by utilizing supercritical carbon dioxide with co-solvent. A novel phosphorusnitrogen containing piperazine derivative, tetraethyl piperazine-1,4-diyldiphosphonate (pdp) and a sulfur-nitrogen containing derivative, tetramethyl piperazine-1,4-diyldiphosphonothioate (pdpt) were synthesized, and their chemical structures were confirmed by nuclear magnetic resonance ( 1 H and 13 C NMR) and elemental analysis. pdp and pdpt were then used to treat cotton fabric processed in scCO2. Thermogravimetric analysis (TGA), vertical flame test (ASTM D6413-08), and limiting oxygen index (LOI, ASTM D2863-09) were performed on the treated cotton fabrics, and showed promising results. When the treated fabrics were tested using the vertical flame, we observed that the ignited fabrics self extinguished and left behind a streak of char. Treated higher add-on fabrics were neither consumed by flame, nor produced glowing ambers upon self extinguishing. The results from cotton fabrics treated with new phosphorus-nitrogen containing piperazine derivatives demonstrated a higher LOI value as well as higher char yields due to the effectiveness of phosphorus and nitrogen as a flame retardant for cotton fabrics. Furthermore, SEM was employed to characterize the chemical structure on the treated fabrics as well as the surface morphology of char areas of treated and untreated fabrics.