Thermal behaviour of palladium complexing polyacrylamidoxime polymer

A fibrous material with metal complexing ability, suitable for retention, concentration and recovery of the palladium ions from acidic aqueous solutions, was prepared by partially converting the nitrile groups of a polyacrylonitrile fibre into amidoxime groups. The thermal behaviour of the resulting polyacrylamidoxime fibre in comparison with its polyacrylonitrile precursor, as well as that of the sorbent material after the retention of palladium ions were studied by thermogravimetric analysis and differential scanning calorimetry. By using the thermogravimetric data the activation energy of the thermo-oxidative decomposition was evaluated by Coats-Redfern and Levi-Reich methods. The introduction of amidoxime groups into the structure of the polyacrylonitrile fibre decreases its initial thermal stability, but has a rather little influence on the main step of its thermo-oxidative decomposition. The polyacrylamidoxime fibre containing palladium ions retained by complexation exhibits a better initial thermal stability than the original polyacrylamidoxime fibre due presumably to the crosslinking formed by intermolecular complexation of the ions; by contrast, the palladium ions have a strong catalytic effect on the reactions involved in the main step of polyacrylamidoxime fibre decomposition. (C) 2001 Elsevier Science Ltd. All rights reserved.