| Abstract: | The structure and properties of oriented (draw ratio 12:1) polyethylene filaments, produced by drawing electron-irradiated isotropic monofilament, have been studied by rubber elasticity measurements, x-ray diffraction, differential scanning calorimetry, and tensile creep behavior. The apparent molecular weight M?c between network junctions, has been calculated from the Flory and Mooney–Rivlin theories, as a function of dose, and extrapolation back to zero dose gives a value of about 16,000 g mol?1, which is related to the molecular weight between entanglements in the linear polymer (M?n 28,000). The WAXS and SAXS patterns of the unirradiated and 6.0 Mrad samples were identical, indicating an equivalent extent of crystallite orientation and a constant long period of about 170Å. Up to a gel dose of 2.4 Mrad, the degree of crystallinity (DC) of the drawn filaments remains constant, but the melting temperature Tm decreases slightly owing to network junctions at the fold surfaces. Above the gel dose, DC drops significantly and Tm falls more sharply, as a result of crystallite distortion. Irradiation dramatically affects the creep behavior, decreasing the equilibrium creep rate by up to four orders of magnitude. For all samples, the constant-flow behavior can be described by a combination of two activated processes in parallel: one associated with the amorphous network and the other with the crystalline regions. Irradiation increases the activation volume of the process occurring in the crystal and is ascribed to an increase in crystallite imperfections. |
