Structural changes and melting behavior of γ-irradiated polyethylene

The structural changes and melting behavior of high density polyethylene irradiated at room temperature were studied by X-ray diffraction and differential scanning calorimetry up to about 4000 Mrad. The melting point and the heat of fusion were depressed by irradiation. A monotonic lattice expansion and an increase in overall specific volume with increasing dose, which lead to a decrease in the specific volume of the amorphous region, were also observed. These changes are thought to be caused by the formation of crosslinks near the surfaces of crystallites and in the amorphous region. The melting point depression can be explained by the effects of lattice distortion and crosslinks outside the crystallites introduced by irradiation. Above 1000 Mrad, a phase transformation into the hexagonal form was observed below the melting point. (author)