Andrady Anthony L, Hamid Halim S, Torikai Ayako
Research Triangle Institute, Research Triangle Park, NC 27709, USA.
Photochem Photobiol Sci. 2003 Jan;2(1):68-72. doi: 10.1039/b211085g.
The outdoor service life of common plastic materials is limited by their susceptibility to solar ultraviolet radiation. Of the solar wavelengths the UV-B component is particularly efficient in bringing about photodamage in synthetic and naturally occurring materials. This is particularly true of plastics, rubber and wood used in the building and agricultural industries. Any depletion in the stratospheric ozone layer and resulting increase in the UV-B component of terrestrial sunlight will therefore tend to decrease the service life of these materials. The extent to which the service life is reduced is, however, difficult to estimate as it depends on several factors. These include the chemical nature of the material, the additives it contains, the type and the amount of light-stabilizers (or protective coatings) used, and the amount of solar exposure it receives. Concomitant climate change is likely to increase the ambient temperature and humidity in some of the same regions likely to receive increased UV-B radiation. These factors, particularly higher temperatures, are also well known to accelerate the rate of photodegradation of materials, and may therefore further limit the service life of materials in these regions. To reliably assess the damage to materials as a consequence of ozone layer depletion, the wavelength sensitivity of the degradation process, dose-response relationships for the material and the effectiveness of available stabilizers need to be quantified. The data needed for the purpose are not readily available at this time for most of the commonly used plastics or wood materials. Wavelength sensitivity of a number of common plastic materials and natural biopolymers are available and generally show the damage (per photon) to decrease exponentially with the wavelength. Despite the relatively higher fraction of UV-A in sunlight, the UV-B content is responsible for a significant part of light-induced damage of materials. The primary approach to mitigation relies on the effectiveness of the existing light stabilizers (such as hindered amine light stabilizers, HALS) used in plastics exposed to harsh solar UV conditions coupled with climate change factors. In developing advanced light-stabilizer technologies, more light-resistant grades of common plastics, or surface protection technologies for wood, the harsh weathering environment created by the simultaneous action of increased UV-B levels due to ozone depletion as well as the relevant climate change factors need to be taken into consideration. Recent literature includes several studies on synergism of HALS-based stabilizers, stabilizer effectiveness in the new m-polyolefins and elucidation of the mechanism of stabilization afforded by titania pigment in vinyl plastics.
普通塑料材料的户外使用寿命受其对太阳紫外线辐射的敏感性限制。在太阳光谱波长中，UV - B成分在导致合成材料和天然材料发生光损伤方面效率特别高。对于建筑和农业行业使用的塑料、橡胶和木材来说尤其如此。因此，平流层臭氧层的任何损耗以及由此导致的地面阳光中UV - B成分的增加，都将倾向于缩短这些材料的使用寿命。然而，使用寿命缩短的程度很难估计，因为它取决于几个因素。这些因素包括材料的化学性质、所含添加剂、使用的光稳定剂（或防护涂层）的类型和数量，以及所接受的阳光照射量。伴随的气候变化可能会使一些可能接收更多UV - B辐射的地区的环境温度和湿度升高。这些因素，尤其是较高的温度，也众所周知会加速材料的光降解速度，因此可能会进一步限制这些地区材料的使用寿命。为了可靠地评估臭氧层损耗对材料造成的损害，需要对降解过程的波长敏感性、材料的剂量 - 反应关系以及现有稳定剂的有效性进行量化。目前，对于大多数常用塑料或木材材料，用于此目的所需的数据尚不具备。一些常见塑料材料和天然生物聚合物的波长敏感性数据是可用的，并且通常表明（每光子的）损伤随波长呈指数下降。尽管阳光中UV - A的比例相对较高，但UV - B含量却是材料光致损伤的重要部分。缓解措施的主要方法依赖于用于暴露在恶劣太阳紫外线条件下的塑料中的现有光稳定剂（如受阻胺光稳定剂，HALS）的有效性以及气候变化因素。在开发先进的光稳定剂技术、更耐光等级的普通塑料或木材的表面保护技术时，需要考虑由于臭氧层损耗导致的UV - B水平增加以及相关气候变化因素同时作用所造成的恶劣风化环境。最近的文献包括几项关于基于HALS的稳定剂的协同作用、新型间规聚烯烃中稳定剂的有效性以及二氧化钛颜料在乙烯基塑料中提供稳定作用的机制的研究。
