There are many types of fluorescent whitening agents, and they are suitable for various fiber products and have many different usages and dosages. Although the chemical structure and performance of different types of fluorescent whitening agents are different, the whitening principles for products such as fibers are the same.
Since the fluorescent whitening agent is a whitening product, why is it that too much use in the fabric can not whiten it and cause the whiteness to decrease? The molecule of the fluorescent whitening agent contains a conjugated double bond system, which has good planarity. This special molecular structure can absorb invisible ultraviolet rays under sunlight, thereby reflecting and emitting blue-violet light, and finally on the fiber fabric. Combined with the yellow light, it emits white light that is visible to the naked eye, so as to achieve the effect of removing yellow and whitening.
The main brightening principle of optical brighteners is optical brightening, not chemical bleaching that produces chemical reactions. Therefore, before using optical brighteners in fabrics, proper chemical bleaching can make the optical brighteners work. The biggest effect. The content of ultraviolet rays in sunlight irradiated on the fabric and the concentration of the fluorescent whitening agent in the fabric are explained according to the whitening principle of the whitening agent. The above two points determine the whitening effect of the optical brightening agent in the fabric.
When the UV content in the sunlight is sufficient, the concentration of the fluorescent whitening agent in the fabric is within the applicable range, and the whitening effect of the product increases as the concentration of the fluorescent whitening agent increases. When the concentration of the fluorescent whitening agent reaches a certain optimal standard in the fabric, the whitening effect is the best, and the highest whiteness value that the current product can achieve can be obtained. When the concentration of the fluorescent brightener exceeds the critical value that the current fabric product can use, the whiteness of the fabric will turn yellow or even show the original color of the brightener. So the optimal concentration used in the fabric is called the yellowing point of the brightener. So why does the whiteness decrease when the amount of brightener used in the fabric is too much?
When the concentration of the fluorescent brightener on the fabric product reaches the yellowing point of the brightener, the intensity of the blue-violet light reflected by the brightener and the yellow light on the fabric complement each other, and the brightening effect is the best at this time of. And when the concentration exceeds the yellowing point of the brightener, the reflected blue-violet light exceeds the yellow light of the fabric, resulting in excessive blue-violet light, and the final thing the naked eye sees is a significant decrease in whiteness or even yellowing.
Therefore, before adding the fluorescent brightener to the product, continuous samples should be taken to test the yellowing point of the current type of brightener in fabrics and other products. So as to adjust the optimal addition amount to maximize the whitening effect.
Post time: Nov-10-2021