The crucial role of temperature on the weathering of polyethylenes was illustrated in a recent study on desert exposure of polyethylene films. The air temperature varied in the range of 26 C to 36 C during the period of exposure. Figure 7.1 shows the change in extensibility of the films obtained for each set of samples. Samples kept at the lower temperature deteriorated much slower relative to those at ambient temperature although both were exposed to the same dose of solar UV radiation. It is the synergistic effect of high temperature and solar UV radiaion that is responsible for the rapid degradation of the polyethylene films under these conditions.
Water acting as a heat sink is able to maintain low sample temperatures, retarding deterioration.
Any serious assessment of the extent of anticipated photodamage requires quantitative information pertaining to each of these. The solar radiation data and the temperatures for most locations of interest are reliably known. Figure 7.2 shows the basic steps involved in photodamage and illustrates the various strategies commonly used to mitigate light-induced degradation of polymers. Change in the extensibility of polyethylene film samples exposed in Dhahran, Saudi Arabia. Improved stabilizers are introduced into the market periodically.