Structural relaxation in polyethylene in the presence of silver oxide investigated by positron-lifetime spectroscopy

Structural relaxation in high-density virgin polyethylene and silver oxide doped polyethylene has been investigated using positron annihilation lifetime technique at 30 degreesC and 100 degreesC ageing temperatures. The ortho-positronium (o-Ps) pick-off lifetime and its intensity show no changes with isothermal ageing time for the virgin sample at 30 degreesC. In the case of the doped sample at 30 degreesC, the o-Ps intensity shows exponential relaxation in the short-time range. At 100 degreesC, the o-Ps lifetime remains almost constant, whereas the o-Ps intensity exhibits an exponential character in the virgin and doped samples, which can be fitted with exponential decay curves. The relaxation times have been evaluated from the structural relaxation function constructed using o-Ps intensity values, and the stretching exponent beta has been estimated using the Kohlrausch-Williams-Watts (KWW) function. Positron results indicate that the stretching exponent beta seems to be temperature dependent