Recyclable Reactive Dyeing Of Cotton And Wool In Non-Aqeuous Solvents

Reactive dyes are dominant dyestuffs in the cellulose dyeing and are gaining more and more popularity in coloration of protein fibers. The ever increasing dye consumption also indicates the reactive dyes would have a great market potential in future dyeing industry. However, the reactive dyes are prone to hydrolysis in conventional dyeing system since reactive functional groups would react with the water molecules. The inevitable hydrolysis reduces the dye utilization rate and the hydrolyzed reactive dyes increase the difficulty of dyes removal during the wash-off process. It has been reported that up to 60% reactive dyes could be lost due to hydrolysis and disposed as the pollutions. Removal of unfixed dyes requires a huge amount of water in order to meet the desirable colorfastness. In summary, the traditional reactive dyeing suffers from the problems such as dye hydrolysis, excessive salt and water consumption, which cause harmful impacts on the environment. These environmental problems need to be addressed to make the textile industry more sustainable.In the first chapter of this dissertation, the history of non-aqueous dyeing and characterization methods were reviewed. Using non-nucleophilic solvents as the dyeing medium was proposed as the solution to the hydrolysis problem without compromising the dyeing quality. Based on what was known for dyeing cotton, the swelling step is the basic process in a fully recyclable reactive dyeing, which has the crucial effect on the final color depth and color fastness.The swelling phenomenon of cellulose in non-aqueous medium was discussed in this dissertation. Currently, insufficient cellulose swelling became the bottle neck which held back development of all following steps in the non-aqueous dyeing. In this study, the lower color depth and lack of fastness of the dyed fabrics were attributed to the fact that the non-nucleophilic solvents could not open up the holes in cellulose. The swelling degree of cellulose was characterized and its effect on dyeing properties was investigated.The results demonstrated the weight of fabric after centrifugation, the change in diameterand dyeing kinetics were corresponded to the cellulose swelling degree well. After screening and dyeing conditions optimization, N, N- Dimethyl acetamide(DMAc) was selected from a group of non-nucleophilic solvents as the optimal swelling solvent.Compared with the swelling pretreatment at room temperature, DMAc swelling at 150 °C for 1 hour could improve 180% in the weight gain, 63% in fiber diameter and 6 times acceleration in dyeing rates. On the other hand, multiple regression analysis indicated that hot DMAc was also essential in rinsing processes to obtain excellent dye fixation and efficient dye removal.Dimethylsulfoxide(DMSO) was used to replace DMAc as the pretreatment solvent because of its strong ability in swelling cellulose at ambient temperature and favorable EHS attributes. The third part of the dissertation focused on the realization of fully recyclable non-aqueous reactive dyeing process. Both dyeing residuals and rinsing liquor were reused. The recyclable dyeing process could minimize the disposals and prevent environmental problems in a source control way by design. Excellent dye exhaustion,hydrolysis free and low salts usage were achieved with a binary dyeing medium consisting of the proper amount of DMSO and dimethylcarbonate(DMC). The new process approached the goal of zero discharge, and total wastes were reduced by more than 99.7% comparing to the traditional aqueous dyeing. The process was also found to be generally applicable to both vinyl sulfone and triazine dyes with consistently good shade build-up and colorfastness. In addition, the reuse of unfixed dyes could improve the rate of utilization and reduce the dye consumption.The forth part of the research focused on the fixation mechanism of both vinyl sulfone(VS) dyes and Monochlorotriazine(MCT) dyes. In vinyl sulfone dyes fixation study, it was found that the nucleophilic addition of cellulosic hydroxyls to a VS dye required the formation of an activated intermediate of the dye and an amine base, which was distinctive from the general base catalysis observed in conventional wet processing.Diazabicyclo[2.2.2]octane was identified as the most effective base for promoting the reaction. The formation of the amine-dye intermediate was also confirmed for base promoted MCT dye fixation using HPLC. The mechanisms of the amine-promoted dye fixation were modeled using density function theory(DFT) calculations. The quaternary ammonium catalysis effect on intermediate formation was observed. Based on the result,both vinyl sulfone dyes and triazine dyes formed activated intermediate in non-aqueous medium. The current work also represents the first attempt to combine computational and experimental methods to investigate the fixation mechanism of the MCT dye on cotton in an organic solvent.Wool is the second most important natural fiber that could also be dyed with reactive dyes. To expand the scope of non-aqueous recyclable reactive dyeing, wool fabric pretreated with dimethylsulfoxide(DMSO) was characterized and its dyeing behavior in non-aqueous green solvents was investigated in the last chapter of this dissertation. Reactive dyeing of wool in deep shades is challenging because the mandatory alkaline aftertreatment to match the fastness of mordant dyes inevitably causes damage to wool keratin. The poor colorfastness could be solved by replacing water with organic solvents as the dyeing medium. Covalent fixation is predominantly favored in solvent dyeing so that excellent colorfastness is achievable at any given shade without aftertreatment. Compared with aqueous dyeing, solvent dyeing was found to give30% higher covalent fixation on average, which translated to better colorfastness(0.5-1grade) at higher color depth(ΔK/S = 1.3-4.9). In addition, SEM, XRD and ATR-IR results indicated that DMSO pretreatment induced morphological and structural changes of wool which was in favor of dyeability. The findings are crucial to the phasing-out of metal-containing dyes for eco-friendly wool dyeing.In conclusion, the swelling problem in non-aqueous system was solved in this research, which removed the bottle neck in non-aqueous dyeing of nature fibers. With sufficient cellulose swelling, good color depth and fastness could be achieved in the binary non-aqueous solvent system. The fully recyclable dyeing process developed in this research meets the 3R(Reduce, Reuse, Recycle) principle. Multi-cycles dyeing sequences demonstrated that the novel non-aqueous reactive dyeing technology had the advantages of being eco-friendly, reasonable in cost and highly efficient. It was encouraging that the developed dyeing process was also applicable to reactive wool dyeing. High color shade and fastness could be achieved without heavy metal ions.According to our research, this non-aqueous dyeing system is applicable to the most important natural fibers dyeing to eliminate the reactive dye hydrolysis, and has a great potential in environmental protection. As a result, it is worthy to be further pushed toward industrialization.