Thermal degradation of mercury chelated polyacrylamidoxime

摘要

The aim of this work was to explore the possibilities of using a polyacrylamidoxime fibre, obtained by chemical modification of a commercially available polyacrylonitrile fibre, as a convenient material for the retention of mercury ions from acidic aqueous solutions. The influence of several factors (concentration, pH and type of anion) on the efficiency of retention, as well as on the structure and thermo-oxidative degradation of the resulting polyacrylamidoxime-mercury ion chelates was studied by elemental analysis, IR spectroscopy and dynamic thermogravimetry. The retention provided by AOPAN is complete for mercury ions as chloride, whereas partial (irrespective of concentration and pH) for these ions as nitrate. In comparison with the polyacrylamidoxime fibre, the mercury chelated fibre exhibits higher initial temperature of decomposition, presumably because of the crosslinking generated by the intermolecular complexation of the ions, but subsequently its thermal stability is lower, due mainly to the release of decomposition products with high volatility, assumed to consist of neutral compounds derived from the reactions involving the anions. It appears that the thermal stability of the polymeric chains crosslinked through mercury ions is better when the anions are of chloride type than when they are of nitrate type, as the crosslinks break predominantly in the main step of the process in the former case, whereas during the first step in the latter.