Characterization of flame-retarded polymer combustion chars by solid-state13C and29Si NMR and EPR

We report here on the results of our continuing effort to study the flame-retardant mechanism of silica gel and potassium carbonate. These additives reduce the flammability of a wide variety of common polymers such as polypropylene, nylon, polymethylmethacrylate, poly(vinyl alcohol), and cellulase. In an effort to determine how these additives reduce polymer flammability, we have used electron paramagnetic resonance spectroscopy and solid-state C-13 and Si-29 nuclear magnetic resonance spectroscopy to characterize the combustion chars or residues. These data indicate that, in the case of poly(vinyl alcohol), the additives do not change the type of char formed, but they do change the rate of char formation relative to the rate of fuel generation. We also found that, using only CP/MAS C-13 NMR, there can be significant intensity distortions which complicate interpretation, if the char is hydrogen depleted and contains paramagnetic centres. (C) 1998 John Wiley & Sons, Ltd.