Thesis Details

Thesis Title: Evaluation of current technologies for modifying cotton to affect fiber reactive, acid, and direct dyeing
Thesis Author: R. Scott Bagley
Abstract: During recent years the importance of natural fibers in the marketplace has increased dramatically, with cotton being a major force in this transformation. Over the past ten years, cotton-has captured one-third of the total textile fiber market and is the fiber of choice in the apparel industry. There are several methods which are prevalent in the dyeing of cotton in industry today, among these are fiber reactive and direct. These dyes provide a wide shade range and bright colors with relatively good fastness to light and water. However, these dyeing systems are confounded by certain factors. These factors are due to the nature of the dyeing systems and the methods used to facilitate the reactions. Fiber reactive dyeing requires the reaction be carried out at an extremely alkaline pH and in the presence of large amounts of electrolytes, usually common or Glauber's salt. Direct dyes, although carried out at a neutral pH, require significant amounts of salt also. In addition, certain portions of the dyestuff are not consumed in the dyeing reaction and therefore remain in the bath after the dyeing. These contaminants in the effluent must then be dealt with, which poses a tremendous environmental burden. The objectives of this thesis were to study the impact of chemically modifying cotton to alter the dyeability using fiber reactive and direct dyes and also to study the feasibility of dyeing the modified cotton with acid dyes, which are not normally used with cotton. Two monomers of different chemical structure and one polymer were applied to 100% cotton twill fabric using a pad-dry-cure technique and the samples were then dyed using a fiber reactive, acid and direct dye. The concentration of the chemicals was varied, in addition to various parameters of dyeing. In addition, the effects of DMDHEU were investigated. The fiber reactive dyeings were performed at three pH levels, 3.0, 6.0, and 12.0, and three levels of salt-concentration ranging from the manufacturers recommended amount to zero. Directs dyeings were perfomed at three levels of salt concentration ranging from the manufacturers recommended amount to zero. The acid dyeings were performed at two levels pH, 3.0 and 6.0. Pre-treated undyed samples were tested to ascertain any changes in the whiteness or tear strength the chemical treatments may have incurred. The dyed samples were tested for KlS, eIE L* a* b* values, lightfastness, washfastness, and nitrogen content. The results of this thesis revealed that cotton can be modified using compounds containing a quaternary nitrogen function without any significant detrimental affects to the whiteness or tear strength of the fabric. The dyeability of the cotton using all dye classes was significantly affected by the use of these chemical modifications. The concentration of the chemical added and the presence of DMDHEU was also found to significantly affect dyeability. Fiber reactive dyeings could be performed at a relatively neutral pH without the use of salt, with lightfastness and washfastness results comparable to those of untreated cotton. Direct dyeings were also conducted using little or no salt and without sacrificing lightfastness or washfastness. In general, acid dyeings of the cellulose were not as successful as the other two dye classes, although those samples which did dye to a significant degree had acceptable lightfastness and washfastness results. Using the dyeing quality data and the nitrogen content data, proposals for the complex reaction mechanisms were presented. These chemical modification treatments significantly reduced the concentration of residual dyestuff in the bath. This factor coupled with the excellent dyeing results of the fiber reactive and direct dyeings indicate that a modification of the cotton fabric prior to dyeing will significantly reduce the amount of contamination in the effluent from these processes.