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Analysis of The Textile Colorfastness to Washing
2016-08-05 08:03  Clicks:
Comparison of the testing method of colorfastness to washing
 
Colorfastness to washing is one of the most common assessment project of color fastness. Colorfastness to washing refers to the color fading degree of the colored fabric after soap washing under the specific condition, including the original sample fading and white fabric staining these two evaluations items. Original sample fading means the colored fabric’s colorfastness before and after soap washing; white fabric staining means to sewing and stacking the white fabric with the colored fabric and washing them together, then to analysis the white fabric staining degree caused by colored fabric fading. The degree of fading or staining should be tested under the specified light source and rate it by the standard gray card. There are totally 5 grades, the grade 5 is the best one, garde 1 is the worst.
 
The structure of dyes, dyeing and post treatment relationship with the colorfastness to washing. 
 
In the routine testing, a considerable part of the textiles, including cotton, wool, polyester, nylon and blended fabrics, as well as the fabric with elastic spandex, the staining degree to nylon and acetate fiber paste lining is grade 3 or lower than grade 3. Although the dyes and dying process for different fiber materials are different, but the issue are quite similar. This is mainly related to the transfer of fabric floating color and partial colored fiber particles, and therefore also associated with the dye, the dyeing process and post-treatment process.
 
The colorfastness to washing of the reactive dyeing products is good or bad depends on the unfixed dye
 
Take the reactive dyes as one example, theoretically, the dyes and fiber formed a covalent bond, the dyes desorption, fading and bleeding was not easy to be caused by washing. Therefore,  the colorfastness to washing of the reactive dyeing products is depend on the amount of unfixed dye (hydrolysed dyes and a small amount of unreacted dyes). If the hydrolysed dyes could not be removed entirely, the fading will continue in the follow-up washing. The soap washing colorfastness is also related to the bond making stability of the bonding dyes, the bond breaking will also occur the color fading after washing. Therefore, the most important factor that effect the soap washing colorfastness is the dye’s structure and property, then is the dying process and the after treatment processing. The reactive dye has high fixation rate, or we can say the hydrolysis rate is slow, the amount of hydrolysed dyes is less and then the amount of dyes need to be washed off is also less. The unfixing dyes and the hydrolysed dyes has low substantivity, good water solubility, not easy to stain and wash off. If the dye has very high concentration, the dye residuals volume will be much and not easy to be washed off.
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