The lightfastness tester can be used to evaluate the effect of sunlight on the lightfastness of dyes. QINSUN can provide lightfastness tester. Welcome customers who have questions. Sunlight is the main cause of dye fading. The process of sun photofading is mainly due to the photooxidation reaction or photoreduction reaction of dye chromophoric groups such as azo bonds, and the simultaneous action of these two reactions.
Photo-oxidation of dyes is mainly the oxidation of dyes by activated oxygen. In this reaction, the formation and speciation of oxygen in the active state becomes the main object of investigation.
Among them, the mechanism (1) is believed to be due to the quenching of the photosensitive dye and the triplet oxygen, and the generated singlet oxygen undergoes an oxidation reaction with the dye.Mechanism (2) believes that photo-oxidation results from the fact that after the dye is excited by light, the dye molecules in the excited state undergo an electron transfer reaction with triplet oxygen and then generate negatively charged oxygen free radicals to react.
Although the general research considers singlet oxygen as the main inducing factor of photo-oxidation reaction, in fact, the photo-oxidation reaction of dyes is very complicated, depending on different dyes, different fibers and different external environments vary with each other .
2. Photo Reduction
Photo Reduction Dye blurring is another important way of photo blurring, the mechanism is as follows (take azo dyes as an example).
Compared to the photo-oxidation process, the photo-reduction process is less discussed in the literature, and the dyes on proteinIt fibers (such as wool and silk) and some hydrophobic polymer fibers can undergo photoreduction mainly due to the presence of reducing groups on the fiber (amino group, etc.), and reduce the dye to generate aromatic amines. In addition, photoreduction occurs particularly readily in the environment where sweat is present, which is also due to the effect of a small amount of reducing amino acids in sweat.
3. The effect of sunlight composition on the lightfastness of dyes
The portion of sunlight that can cause photofading of dyes is mainly ultraviolet and visible light.
When there is no ultraviolet light, the amount of dye fade (UV%) is reduced by an average of 22.5%, and the average amount of color fade (O2%) is reduced by 41% when there is no O2, while in the absence of O2 and ultraviolet rays (UV+ O2%) can be reduced by an average of 69.5%. Therefore kcan be determined according to UV% that the light fading caused by the combined action of visible light and O2 can amount to 80%. At the same time, after calculating the average value of the above dye fade reduction, an approximate equation can be obtained:
UV+O2% fade reduction ≈ UV% fade reduction + O2% fade reduction
This shows that ultraviolet light can fade the dye in the absence of oxygen, otherwise the above formula
and relationships cannot are being reached. Visible light, on the other hand, must react to some extent in the presence of oxygen. Of course, considering that the vacuum condition in S.N.Batchelor et al.'s experiment is only 2000-4000Pa (vacuum with water pump), there may also be certain errors in this test result. But it can also be deduced that the mechanism of action of ultraviolet lightand visible light on dyes is likely to be different.