Preparation of halogen-free flame retardant polyacrylonitrile via hydrolyzing and grafting with diphenylphosphinyl chloride

Halogen-free flame retardant polyacrylonitrile (PAN) was prepared via hydrolyzing the nitrile groups of PAN using aqueous sodium carbonate solution/hydrogen peroxide followed by grafting with diphenylphosphinyl chloride. The structure of original PAN, hydrolyzed PAN (HPAN), and flame retardant PAN (FR-PAN) samples were characterized using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and 1H NMR spectroscopy. The thermal properties of the materials were assessed using thermogravimetric analysis. The FTIR spectroscopy indicates that a carbonyl group is present in hydrolyzed HPAN and some characteristic PAN absorption peaks decreased slightly upon hydrolysis. The XPS results show that FR-PAN contained phosphorus, indicating that diphenylphosphinyl chloride has been grafted onto HPAN, which is in accordance with the phenomenon of the self-extinguishing phenomena of FR-PAN during burning experiments. The TG curves indicate the presence of a char residue for FR-PAN of 45% at 800 °C, a higher char residue than that of original PAN (39%). Therefore, FR-PAN displays better thermal stability and char forming capability than does the untreated polymer.