Effects of γ-ray irradiation on polypropylene

The authors have found that the G-value of free radical formation by γ-ray irradiation on polyolefin depends on the higher order structure. Therefore, efforts were made to separately observe the changes in the amorphous and crystalline phases by γ-irradiation using visco-elastic measurement, differential scanning calorimetry, and X-ray method. Isotactic polypropylene was chosen as the material. The drawn and bulk samples were irradiated by γ-ray of 60Co at room temperature. Wide angle X-ray diffraction was measured to estimate the lattice constant and the halfwidth of the diffraction peak. The results obtained were discussed for the change of dynamic loss modulus E'' with temperature for the bulk samples, irradiation effects on the viscoelastic behavior of the drawn samples, and thermograms for the undrawn and drawn samples. Polypropylene has been classified as a cross-linking type polymer. In the amorphous phase, cross-linking occurs to increase the temperature location of αa absorption. While it was found that crystal imperfection was introduced by irradiation from the illustrated facts. This crystal imperfection can be introduced by two mechanisms, (1) cross-linking formation between adjacent chains, and (2) chain scission to form chain ends. The mechanism (2) seems to be responsible for the crystal imperfection resulting in decrease of maximum temperature in polypropylene. (Wakatsuki, Y.)