Miscibility of poly(vinyl alcohol)/polyacrylamide blends before and after gamma irradiation

Films of polymer blends having various contents of poly(vinyl alcohol) (PVA) and polyacrylamide (PAM) were prepared by the solution casting technique using water as a common solvent. The thermal, mechanical and morphological properties of these blends before and after exposure to various doses of gamma radiation, up to 100kGy, have been investigated. The visual observation and reflectance measurements show that PVA/PAM. blends are miscible over a wide range of composition. Moreover, the differential scanning calorimetry (DSC) thermograms show only a single glass transition temperature (T-g), but not those of PVA or PAM homopolymers, giving further support to the complete compatibility of such blends. The T-g of PVA/PAM. blends decreases with increasing content of PAM but increases after exposure to gamma irradiation, indicating the occurrence of crosslinking. These findings were demonstrated by the scanning electron micrographs of the fracture surfaces and the tensile mechanical properties. The TGA thermograms and percentage mass loss at different decomposition temperatures show that unirradiated PVA homopolymer possesses higher thermal stability than PAM homopolymer and their blends within the heating temperature range investigated, up to 250degreesC. An opposite trend is observed within the temperature range 300-500degreesC. In general, the thermal stability of homopolymers or their blends improves slighly after exposure to an irradiation dose of 100kGy. These findings are clearly confirmed by the calculated activation energies of the thermal decomposition reaction of the homopolymers and the blends. (C) 2003 Society of Chemical Industry.