Synthesis and Application of Azo Dyes in Supercritical Carbon Dioxide
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Date
2006-08-08
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Abstract
This dissertation is concerned with the utilization of supercritical carbon dioxide (SC-CO2) for the synthesis of azo dyes and their application to textile substrates. One of the major benefits to diazotization and coupling in SC-CO2 and small amounts of water includes elimination of mineral acid as a proton source for the diazotization reaction, thereby negating the requirement of neutralization and effluent treatment of highly colored and electrolyte-concentrated effluent.
The work was divided into five main parts. In the first part, ten common arylamines were selected to study the effect of type and placement of substituents on the product yield of a series of simple azo dyes using a SC-CO2-water medium to act as both solvent and proton source. Azo dyes from arylamines containing nitro- and vinylsulfonyl- substituents in the para-position relative to the diazotizable amino group were easily synthesized in SC-CO2 in reasonable yield. The synthesis of azo dyes in SC-CO2 was dependent on a combination of basicity, solubility and steric hindrance around the amino group to be diazotized.
The second part involved optimization of the reaction yield of a vinylsulfonyl-based disperse reactive dye via a statistical design of experiment. For the reaction system employed, the primary influences on product yield were, by far, water, followed by pressure and time. Temperature had little effect on product yield. The optimized synthetic procedure afforded near complete conversion to the target dye.
Part three demonstrated a new SC-CO2 azoic dyeing method, in which the diazotization and coupling of a simple arylamine, aniline, to form a dye inside cotton fibers was optimized using a statistical design of experiments. It was found that H2O, pressure and dyeing time had a significant effect on shade depth, levelness and fastness properties. Under optimized conditions, the dyed fabrics produced uniform dyeings with high color strength and fastness properties that were comparable to those from conventional aqueous azoic dyeing. Furthermore, the potential wide scope of azoic dyeings using SC-CO2 was demonstrated, with cellulose acetate, viscose, wool and silk all being dyed successfully. However, the coupling component had to be applied to the substrate using a conventional pad-dry procedure.
Part four was an investigation of the effects of temperature and pressure on dyeing nylon 6,6 and wool in SC-CO2 using the vinylsulfonyl fiber-reactive disperse dye under various reaction conditions. In addition, equivalent dyeings were performed using a nonreactive disperse dye analog in order to determine the effects of the reactive group on dye fixation. Nylon 6,6 and wool were effectively and efficiently dyed with a high degree of color strength and fixation. Color strength increased with increasing temperature and pressure for both substrates, with greater than 96% apparent fixation achieved. In a model experiment, the fiber reactive dye was successfully reacted with butylamine in SC-CO2 under the conditions used for dyeing, demonstrating that covalent bond formation between the dye and an aliphatic amine (similar to the nucleophilic groups present on nylon 6,6 and wool) was achieved using this dyeing system. The alkylamine derivative of the dye was characterized by FAB-MS and 1H-NMR.
The final part of this work involved the attempted synthesis of the most important fiber-reactive dye, C.I. Reactive Black 5, in SC-CO2 in the absence of mineral acid by two-step method. It was found that coupling in SC-CO2 was only successful at the 7-position of H acid, and not at the position ortho to the amino group of that coupling component, possibly due to steric hindrance and reduced reactivity at that position.
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azo dye synthesis, Supercritical Carbon Dioxide
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Degree
PhD
Discipline
Fiber and Polymer Science
