NATURAL AND ACCELERATED PHOTOAGING OF LINEAR LOW-DENSITY POLYETHYLENE - CHANGES OF THE ELONGATION AT BREAK

The photoaging of different linear low-density polyethylenes (LLDPEs), namely, ethylene-butene (EB) and ethylene-hexene (EH), has been studied. Experiments have been carried out under natural and accelerated UV exposure. We focused our investigation on the changes of elongation at break and the modifications in the chemical structure (measured by the IR technique) occurring over the photoaging process. Our results showed that the changes of elongation at break were different under the two modes of irradiation from the very beginning of UV exposure; in contrast, the comparison of stoichiometry displayed a small difference in the later stage of UV irradiation. That pointed out the difficulty of establishing a relationship between the buildup of carbonyl groups and the mechanical changes due to UV irradiation, which has been usually attempted. In addition, it appeared that the density, oxygen permeability, and the type of alpha-olefin of the polymer might have an effect upon the elongation-at-break changes. From our data, it can be suggested that the prediction of weathering resistance of polymers can be based on both mechanical changes and modifications in chemical structure to minimize erroneous prediction.