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Increased solar ultraviolet radiation (UV) reaches the surface of the Earth as a consequence of a depleted stratospheric ozone layer and changes in factors such as cloud cover, land-use patterns and aerosols. Climate change is expected to result in a 1.1-6.4 °C increase in average temperature by the end of this century, depending on location. Increased levels of UV radiation, especially at high ambient temperatures, are well-known to accelerate the degradation of plastics, rubber and wood materials, thereby reducing their useful lifetimes in outdoor applications. Plastics used routinely outdoors are generally light-stabilized using chemical additives to ensure their useful lifetimes. Wood products are coated for resistance to UV radiation, since photodamage results in enhanced water-susceptibility and their consequent biodegradation under outdoor exposure. The increased damage to materials due to an increased UV-B (280-315 nm) component in solar radiation reaching the Earth likely can be countered using light-stabilization technologies, surface coatings or, in most instances, by substituting the materials in question with greater UV radiation-resistant materials. However, even if these options could be used with all common materials affected, they will invariably result in higher costs. Reliable estimates of the incremental costs involved depend on the anticipated damage and the effectiveness of mitigation strategies employed. We summarize and assess recent findings on light-induced damage to plastic materials, including wood-plastics composites and nanocomposites. The combined effect of increased UV-B radiation and ambient temperature is of special interest, since these two factors represent particularly harsh environmental conditions for most materials. Advances in approaches to light stabilization of materials are also assessed.

SynopsisPoly( methyl methacrylate) (PMMA) was photolyzed with monochromatic light of wavelengths 260, 280, and 300 nm by the use of the Okazaki large spectrograph. The quantum yield of mainchain scission ( aC8), effects of wavelength, and incident photon intensity on the photodegradation were investigated. It turned out that photodegradation of PMMA took place by the irradiation of 260-300 nm light, but did not by the irradiation at X 2 320 nm. The number of main-chain scission ( N c s ) has a maximum value in the case of the irradiation with 280 nm light. Under the same conditions of wavelength and total photon intensity, a longer-term irradiation with a weaker incident photon intensity tends to yield a greater amount of main-chain scission. A linear relationship was found between the number of main-chain scission and the incident photon intensity. The average values of aC8 obtained in this work were 2.1 X 2.4 X and 4.1 X respectively, for the irradiations a t 260, 280, and 300 nm. It was found that the photoinduced side-chain scission initiates the main-chain scission of PMMA.

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