Thesis Details

Thesis Title: Process Development and Optimization for High Efficiency Fiber Reactive Dyes
Thesis Author: Riley Jo Carrigg
Abstract: Fiber reactive dyes are important in dyeing textiles because they are unequal in their ability to confer bright wetfast shades on cotton fabric. While fiber reactive dyes are commonly employed for this purpose, the use of these dyes can introduce high costs and environmental concerns. For example, their fixation levels can be as low as 50% and high salt levels are typically needed to achieve desired shades. Thus, a mechanism for increasing fixation and exhaustion efficiencies in an economical way would enhance the value of these dyes to the textile industry. With these points in mind, researchers at North Carolina State University have studied a reactive dye modification that holds promise for achieving desirable exhaustion and fixation efficiencies. Specifically, the reactivity and affinity of some widely used dichlorotriazine (DCT) reactive dyes was enhanced using a straightforward 2-step process to convert commercial dyes to structures of types 1-4. In laboratory dyeing studying it was determined that type 2 dyes gave the best results in affinity and shade depth assessments. It remained to be shown that these dyes could be applied in an industrial dyeing setting. This thesis research focuses on applying the type 2 modified dyes in a commercial-scale manufacturing setting in order to further assess the benefits of the modified dyes. In preliminary studies, laboratory-scale dyeings were conducted to further investigate the color strength relationships between the modified and commercial dyes. As the main thrust of this research, dyeings were conducted in the pilot plant at North Carolina State University in order to simulate a production environment. An optimized batch dyeing procedure was developed for the application of the modified dyes, including optimal temperature, salt and alkali concentrations, time, and bath ratio. It has been found that level dyeings can be readily produced using industrial scale equipment, and there was no adverse change in fastness arising from using the modified dyes in lieu of commercially available DCT reactive dyes. Further, it is clear that high fixation levels and deep shades are obtained using the modified dyes at lower dyeing temperatures and salt levels than commonly employed for the commercial dyes. Reactive dyes are among the most common dye type used in the dyeing of cotton. Although there are many dyes commercially available, the use of these dyes leaves excess pollutants in the wastewater after dyeing, principally, salt and color. The treatment of these pollutants is costly and difficult to conduct. One alternative is to increase the inherit affinity of dyes, thus increasing their exhaustion and fixation, allowing a dyer to use less salt and dye and reduce the residual color in his wastewater. Homobifunctional reactive dyes, synthesized through modification of commercially available dyes showed improved exhaustion and fixation in lab experiments (3). The purpose of this work was to extend previous lab studies into a pilot plant setting to further evaluate the performance of these modified dyes. These pilot plant studies used, as a starting point, a procedure that was determined in the lab to be optimal relative to commercially available dyes and three modified dyes. The use of reactive dyes in cellulosic dyeing is often associated with higher-than-necessary cost and environmental concerns from the discharge of color due to inefficient fixation. To achieve an acceptable level of exhaustion and fixation, high levels of salt are typically used with the reactive dyes currently available on the market. This increases cost due to the cost of the salt and raw material, as well as causing costly and difficult wastewater treatment to be necessary. In addition, high concentrations of salt are very corrosive to batch dyeing machines and other equipment.