EFFECTS OF INCREASED
SOLAR ULTRAVIOLET RADIATION ON MATERIALS
A.L. Andrady (USA), S.H. Hamid (Saudi Arabia), X. Hu
(China) and A. Torikai(Japan)
Summary
Synthetic polymers such as plastics, as well as naturally-occurring
polymer materials such as wood, are extensively used in building construction
and other outdoor applications where they are routinely exposed to sunlight.
The UV-B content in sunlight is well known to adversely affect the mechanical
properties of these materials limiting their useful life. Presently their
outdoor lifetimes depend on the use of photostabilizers in the case of
plastics and on protective surface coatings in the case of wood. Any increase
in the solar UV-B content due to a partial ozone depletion would therefore
tend to decrease their outdoor service life. It is the synergistic effect
of increased UV radiation with other factors such as the temperature that
would determine the extent of such reduction in service life. The increased
cost associated with such a change would be felt unevenly across the globe.
Those developing countries that depend on plastics as a prime material
of construction and experience high ambient temperatures are likely to
be particularly affected in spite of the relatively small fractional decrease
in ozone at those locations.
Assessment of the damage to materials,
associated with ozone depletion, requires a knowledge of the wavelength
dependence as well as the dose-response characteristics of the polymer
degradation processes of interest. While the recent literature includes
some reliable spectral sensitivity data little dose-response information
has been reported making it difficult to make such assessments reliably
at the present time. This is particularly true for the naturally-occurring
materials popularly used in construction applicastions.
To maintain polymers at the same useful
lifetime in spite of increased solar UV-B content the amount of photostabilizers
used in the formulations might be increased. This strategy assumes that
conventional stabilizers will continue to be effective with the spectrally
altered UV-B-enhanced solar radiation. While the present understanding
of the degradation chemistry suggests the strategy to have merit, its effectiveness,
in an altered solar radiation environment, has not been demonstrated for
common polymers. The availability of this data is crucial to reliably estimate
the cost of mitigating the increased damage to materials as a result of
a possible partial depletion of the ozone layer using this approach.
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