γ-irradiation effects on the thermal and structural characteristics of modified, grafted polypropylene

The effects of both the degree of grafting and gamma irradiation on the thermal stability and structural characteristic of polypropylene-graft-polyvinylpyrrolidone and polypropylene-graft-polyvinylpyrrolidone modified with alpha-cyano-delta(2-thienyl) crotononitrile were investigated. The employed techniques were thermogravimetric analysis, differential thermogravimetry, and X-ray diffraction. The thermal stability of various polymeric substrates was investigated through the determination of the degradation temperature and activation energy of degradation. The effects of different parameters on the structural characteristics of different films were investigated through the determination of possible changes in the degree of ordering of the polymeric substrates. The results revealed that the thermal stability of the trunk polymer, grafted polymer, and polymer modified by alpha-cyano-delta(2-thienyl) crotononitrile increased progressively with an increasing degree of grafting. The increase was, however, more pronounced for the sample undergoing the lowest degree of grafting. The activation energy of the thermal degradation process remained almost unchanged, and this indicated that the degradation processes of the different films followed almost the same mechanism. The gamma irradiation at a dose of 60 kGy of the sulfur-treated polymeric films [i.e., the polymeric films treated with alpha-cyano-delta-(2-thienyl) crotononitrile] reduced their thermal stability. This conclusion was reached by the consideration of the changes observed in the pre-exponential factor of the Arrhenius equation due to different chemical and gamma-irradiation treatments. The degree of ordering, evidenced by X-ray diffraction measurements of the trunk polymer, grafted polymer, and modified polymer, suffered a significant drop. This drop was much more pronounced for the sulfur-containing polymeric materials. The observed drop in the degree of ordering of the polymeric substrates was taken as a measure of the structure collapse due to a certain treatment (degree of grafting and sulfur inclusion). The gamma irradiation of the sulfur-containing polymeric materials greatly increased their degree of ordering, which reached a value greater than that measured for the trunk polymer. Therefore, it was concluded that the thermal stability increased as the degree of ordering decreased. (c) 2006 Wiley Periodicals, Inc.