The ability of polymeric materials to withstand exposure to sunlight (or artificial light sources that simulate sunlight) and maintain their original physical or chemical properties is referred to as the lightfastness of polymeric materials.
Sunlight is the main external factor that affects the aging of polymer materials. After the polymer material is irradiated by sunlight, it initiates a photochemical reaction, that is, a chain reaction according to the photooxidation mechanism, which causes the polymer to degrade or crosslink two types of irreversible chemistry. The reaction causes deterioration (aging), and the photochemical reaction is generally carried out on the surface (or surface layer) of the material (or sample). First, it causes the aging of the surface polymer material, and gradually develops toward the inner layer as the aging time progresses. The characteristic of photoaging is that the size of the light-receiving area of ​​the material and the amount of light intensity per unit area have a great influence on the aging rate of the material.
The light energy of sunlight varies with wavelength. The shorter the wavelength, the larger the energy. The wavelength of sunlight is divided into three regions: the ultraviolet region ( 150~400nm ), the visible region ( 400~700nm ), and the infrared region (> 700nm ), the wavelength of zui's short ultraviolet light has a large light energy, which is the main factor for the aging of the polymer. Although the ultraviolet light reaching the ground is very small ( less than 50% ), the ultraviolet light with a wavelength below 290nm They are all absorbed by the ozone layer at high altitude. The ultraviolet radiation with a wavelength greater than 290 nm is reached at the ground , 290~400nm. The ultraviolet light in the band is the main cause of the destruction of the sub-chain of cultural and entertainment activities of polymer materials. The infrared light of sunlight accelerates the aging of polymer materials, because the material absorbs infrared light and then transforms into heat energy, which accelerates the aging of the material. Visible light generally cannot cause the destruction of molecular chains of polymer materials, but under certain conditions, it can also cause the degradation of certain high polymers and the destruction of pigment-containing polymer materials. The high polymer used in the coating is exposed to the single factor of sunlight (or artificial light source), and the remarkable phenomenon of zui is loss of light and discoloration.
This article is edited by Beijing Hongda Tianmo Testing Equipment Co., Ltd.
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