Color fastness tester to evaluate the effect of sunlight on the color fastness of dyes to sunlight

Sunlight is the main cause of dye fading. The process of sunlight-induced fading is mainly due to the photo-oxidation or photo-reduction reaction of dye chromophore groups such as azo bonds, and the simultaneous action of these two reactions. of. The light fastness testing-equipment' target='_blank'>tester can be used to evaluate the influence of sunlight on the color fastness of dyes. 1. Photo-oxidation The photo-oxidation of dyes is mainly the oxidation of dyes by activated oxygen. In this reaction, the generation and morphology of activated oxygen become the main research objects. The generation of activated oxygen mainly has the following two ways: Among them, the mechanism (1) is considered to be due to the quenching of the photosensitized dye and triplet oxygen, and the generated singlet oxygen undergoes an oxidation reaction with the dye. Mechanism (2) believes that photo-oxidation is caused by the electron transfer reaction between excited dye molecules and triplet oxygen after the dye is excited by light, thereby generating negatively charged oxygen radicals for the reaction. Although the common research regards singlet oxygen as the main inducing factor of photo-oxidation reaction, in fact, the photo-oxidation reaction of dyes is very complicated, which changes according to different dyes, different fibers and various external environments. 2. Photoreduction The photoreduction fading of dyes is another important way of their photofading, and the mechanism is as follows (take azo dyes as an example). Compared with the photo-oxidation process, the photo-reduction process is less discussed in the literature, and the dyes on protein fibers (such as wool and silk) and a few hydrophobic polymer fibers may suffer from photo-reduction fading, mainly due to the dyes on the fibers. The presence of reducing groups (amino, etc.), and the reduction of dyes to produce aromatic amines. Moreover, photoreduction is also particularly easy to occur in the environment where sweat exists, which is also due to the action of a small amount of reducing amino acids (glutamic acid, etc.) existing in sweat. 3. The influence of sunlight composition on the light fastness of dyestuffs The parts of sunlight that can cause photofading to dyes are mainly ultraviolet and visible light parts. By calculating the average value of the light fading reduction of the three conditions in Table 1, it can be concluded that the average fading amount (UV%) of the dye is reduced by 22.5% when there is no UV light, and the average fading amount (O2%) is reduced by 41% when there is no O2. , and in the absence of both O2 and ultraviolet rays (UV+O2%), the average can be reduced by 69.5%. Therefore, according to UV%, it can be found that the amount of light fading caused by the joint action of visible light and O2 can account for 80%. At the same time, after calculating the average value of the above dye fading reduction, an approximate equation can be obtained: UV+O2% fading reduction≈UV% fading reduction + O2% fading reduction This shows that ultraviolet rays can fade dyes in the absence of oxygen, otherwise the summation relationship of the above formula cannot be achieved. Visible light, on the other hand, needs to react in the presence of oxygen to a certain extent. Of course, considering that the vacuum conditions in the test of S.N. Batchelor et al. are only 2000-4000Pa (pump vacuum), there may be some errors in this test result. However, it can also be inferred that the mechanism of action of ultraviolet light and visible light on dyes may not be exactly the same.
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