EFFECTS OF INCREASED SOLAR ULTRAVIOLET-RADIATION ON MATERIALS

Synthetic polymers, naturally-occurring biopolymers, as well as some other materials of commercial interest are adversely affected by solar UV radiation. Applications of these materials, particularly plastics, in situations which demand routine exposure to sunlight is only possible through the use of light-stabilizers and/or surface treatments to protect them from sunlight. Any increase in solar UV content due to partial ozone depletion will therefore accelerate the photodegradation rates of these materials, limiting their service lifetimes outdoors. The nature and the extent of such damage due to increased UV radiation in sunlight is quantified in action spectra. In spite of the several action spectra for polymers, reported in the research literature, the information is often inadequate to make reliable estimates of the increased damage. The specific formulation of the polymer material, the damage criterion employed, and even the manner in which data are interpreted, can often influence the results. However, it is clear from the available data that the shorter wavelength UV-B processes are mainly responsible for photodamage ranging from discoloration to loss of mechanical integrity in polymers exposed to solar radiation. The molecular level interpretation of these changes remains unclear in many instances. The use of higher levels of conventional light stabilizers in polymer formulations will likely be employed to mitigate the effects of increased UV levels in sunlight. However, such an approach assumes that a) these stabilizers continue to be effective under spectrally-altered sunlight conditions; b) they are themselves photostable on exposure to UV-rich sunlight; and c) they can be sufficiently effective at low enough concentrations to economically serve the purpose. Experimental data bearing on these issues is sparse. Ongoing research, particularly those relating to extreme environment exposure of polymers, is expected to shed more light on these unresolved questions. Substitution of the affected materials by more photostable varieties of plastics and other materials also remains an attractive possibility. Both these approaches will add to the cost of plastic products in target applications. With plastics rapidly displacing conventional materials in numerous applications, this is an important consideration particularly in the developing world.