How to improve the dye fastness of reactive dyes
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Dyeing fastness of Cotton fabric
Let’s first talk about the abrasion fastness of dark colors, such as deep red and black
In most cases, the reason for the low wet rubbing fastness of cotton fabrics is not the shedding of the dye, but the shedding of the fibrils of the cotton after dark coloring, which reduces the appearance fastness. Due to the greater friction resistance of cotton in the wet state, the original fibers fall off and adhere to the stained white cloth. Cotton has less friction resistance in the dry state and less fibril shedding, so problems with dry rubbing fastness are less likely to occur.
When confirming the wet rubbing fastness, use reactive black dye to color and soap the cotton fiber, and then use an organic solvent (dimethylformamide) to conduct an extraction test. Even dyed objects with good dye fixation can sometimes only reach level 2 to 3 in the wet rubbing fastness test. Therefore, it can be considered that poor coloring is not the direct cause of poor wet rubbing fastness.
However, if the dye attached to the fabric surface is not thoroughly soaped, the wet rubbing fastness may sometimes be lower than Level 2. When dyeing dark colors, the dyed object must be thoroughly soaped. Judging from the test results, the wet rubbing fastness limit of dark colors for conventional coloring under general conditions is level 2 to level 3, but it is generally difficult to reach level 3.
As mentioned above, the shedding of fibrils will have a certain impact on the fiber surface state such as the shape of the spinning yarn and the fabric structure. Even if the same dye and depth are used for coloring, there will be a difference of about half a degree. Reducing the friction coefficient on the fiber surface has a certain effect on improving the wet rubbing fastness. Treatment with water-repellent finishing agents such as silicone is also extremely effective. These methods may alter the style or functionality of the fabric and are not suitable for all situations.
In addition, the wet rubbing resistance of polyester fabric is smaller than the dry rubbing resistance. Contrary to cotton, its wet rubbing fastness is high and dry rubbing fastness is low.
Color fastness analysis
Dye-dyed cellulose fibers form chemical bonds with the fibers in the form of covalent bonds. Therefore, theoretically speaking, the covalent bond between the dye and the fiber can give the colored object excellent color fastness. But in fact, the colored products often fade, change color or stain during testing, use, cleaning, and even storage. In particular, the wet rubbing fastness and soaping fastness when dyeing dark colors, and the sun fastness and chlorine bleaching fastness when dyeing light colors are all unsatisfactory.
There are two main reasons for the poor color fastness: one is the problem of the dye itself; the other is the problem of the coloring process.
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