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Effects Of Increased Solar Ultraviolet Radiation On Materials

Andrady, AL; Hamid, SH; Hu, X; Torikai, A

ELSEVIER SCIENCE SA, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY

B-BIOLOGY; pp: 96-103; Vol: 46

King Fahd University of Petroleum & Minerals

http://www.kfupm.edu.sa

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 W-B content in

sunlight is well known to affect adversely 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 the outdoor service life of these materials. 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, so it is

difficult to make such assessments reliably at the present time. This is particularly true

for the naturally occurring materials popularly used in construction applications. To

maintain polymers at the same useful Lifetime in spite of increased solar W-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

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the spectrally altered W-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 these data is crucial for reliably estimating the cost of

mitigating the increased damage to materials as a result of a possible partial depletion

of the ozone layer using this approach. (C) 1998 UNEP. Published by Elsevier

Science S.A. All rights reserved.

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