Synthesis of carborane acrylate and flame retardant modification on silk fabric via graft copolymerization with phosphate-containing acrylate

Summary A novel carborane acrylate monomer (1-acryloyloxyethyl carborane) was synthesized by addition reaction, hydrolysis, and esterification and characterized by proton nuclear magnetic resonance ( 1 H NMR) spectroscopy and Fourier transform infrared spectroscopy (FT-IR) analysis. Subsequently, the carborane monomer and a phosphate-containing methacrylate monomer were applied on the modification of a silk fabric. The heat resistance and flame retardancy of the silk fabric before and after modification were compared. Energy-dispersive X-ray spectrometer (EDS) and FT-IR showed that carborane monomer and phosphate-containing methacrylate were grafted onto the surface of the fibers. The cross-sectional morphology of silk fabrics after burning was observed by scanning electron microscope (SEM), and the flame-retardant mechanism was analyzed. Thermal-gravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis revealed that the thermal stability of the modified silk increased with the increase of the grafting yield. The MCC-2 microcalorimeter (MCC) test showed that, when using 1-acryloyloxyethyl carborane as monomer and blending with phosphate-containing methacrylate, the maximum heat release rate (PHRR) of the modified silk fabric decreased from 97.6 W/g (before grafting) to 51.3 and 45.8 W/g, respectively, and the total heat release (THR) decreased from 10.2 kJ/g (before grafting) to 5.9 and 5.2 kJ/g, respectively. The limiting oxygen index (LOI) test revealed that using 1-acryloyloxyethyl carborane and phosphate-containing methacrylate as mixed monomers to modify the silk fabric obtained good flame retardancy, whose LOI value reached 29.8%.