Thermal and catalytic behaviour of grafted polytetrafluoroethylene (PTFE) pretreated with some transition metal nitrates

Abstract

A hydrophobic PTFE solid material has been grafted with acrylic acid (AAc) via exposure to a dose of 20 kGy gamma radiation. The obtained hydrophilic solid (PTF7E-g-PAAc) was impregnated with a solution containing a known amount of nitrate of cobalt, copper, ferric or nickel. The extent of loading of metal species was fixed at 16 wt.-%, expressed as metal oxide. DTA, XRD, IR and catalysis of CO-oxidation reaction with oxygen have been carried out on the various prepared solids. The results obtained revealed that PTFE melts at 355°C, PAAc in the grafted PTFE melts at 230°C. The presence of cobalt or copper species considerably modified these temperatures; as a result of their complete participation in metal-polymer complexes formation. This effect was much less pronounced in the case of nickel and iron cations. Very strong exothermic peaks were detected in the DTA curves at 260–290°C for Fe, Co, Cu species and at 340°C for Ni species. These strong peaks characterize the thermal decomposition of the metal polymer complex with subsequent formation of free amorphous metal oxide. The catalytic activities measured at 200°C for different solids heated in vacuum at 240°C have been found to vary in the following sequence: Co > C ≫ Fe > Ni. These results were attributed to the extent of different transition metal cations involved in the metal-polymer complex formation, their thermal stability, and the specific activity of the produced corresponding metal oxides.