Study On High-temperature Dyeing Behaviors Of Bis(Monochloro-s-triazine) Reactive Dyes

Due to enormous differences in structures and properties of cellulose and polyester fibers one bath one step dyeing process exists many contradictions in dyeing temperatures, pH values of dye bath, and additions of electrolytes when reactive dyes and disperse dyes are used to dyeing multicomponent-fiber fabrics containing cellulose and polyester. Using two bath dyeing process could ensure dyeing quality but require longer process line, huge energy consuming and a large number of wastewater discharging. One bath one step dyeing process can shorten dyeing time but above-mentioned contradictions, especially problem of low color yield of reactive dyes in high-temperature dyeing, could not be perfectly solved. As alkali dyeing technique of disperse dyes has been developed high-temperature dyeing problems of reactive dyes have been a sticking point for realization of one bath one step dyeing process using disperse and reactive dyes.Solving the problem of low color yield of reactive dyes need to investigate the causes of losses of reactive dyes at high temperature. The losses of reactive dyes in high-temperature dyeing relate to process factors such as dyeing temperature and pH values of dye bath, more important, however, relate to changes of properties of the reactive dyes themselves including changes of reactivity, stability and dyeing thermodynamics and kinetics of the dyes at high temperature. Therefore, these factors need be first of all considerate in solving high-temperature dyeing problems of reactive dyes. With bis(monochloro-s-triazine) reactive dyes used in alkali one bath dyeing process as objects, above-mentioned key questions influencing the high-temperature dyeing properties of reactive dyes including reactivity of hydrolysis reactions, and selectivity of hydrolysis/methanolysis reaction of reactive dyes at high temperature, stability of reactive dyes at high temperature(including stability of dyes in solution and on fibers), high-temperature dyeing thermodynamics and kinetics, and the design of high-temperature dyeing alkali, and so on, were studied systematically in this paper, and some ways to solve these problems were put forward.1. To problem of increasing of hydrolysis reactivity of reactive dyes, hydrolysis reactions of a bis(monochloro-s-triazine) reactive dye(C.I. Reactive Red 120) in excessive alkali buffer solution at different dyeing temperatures(90 ~130°C) and various pH values(pH 8.0~11.0)were studied. Through comparing hydrolysis rate constants kH1 that the bis(monochloro-s-triazine) reactive dye hydrolyzed to monochloromonohydroxy-bis-s- triazine dye and kH2 that monochloromonohydroxy-bis-s- triazine reactive dye hydrolyzed to bis(monohydroxy-s-triazine) dye, relations between hydrolysis temperature and p H value changes and hydrolysis reactivity of reactive dyes were found. The obtained rate constants for the hydrolysis of the dye showed that two hydrolysis rate constants increased with the increase of temperature and pH values, however, hydrolysis rate constants was low when the pH value of the hydrolysis solution was decreased at high temperature. Especially reactivities in these conditions, i.e. 100°C,pH 10.0;110°C,pH 9.5;120°C,pH 9.0;130°C,pH 8.0, were close to the reactivity at 90°C and pH 11.0, indicating that severe hydrolysis of the active groups of the dye could be avoided at high temperatures by lowering the pH value of the dye bath.2. The hydrolysis/methanolysis reactions of bis(monochloro-s-triazine) reactive dye(C.I. Reactive Red 120) in mixed solution of methyl alcohol and alkali buffer at 90°C, pH 11.0 and 130°C, pH 8.0 were studied to solving problem of competition between hydrolysis and methanolysis reaction of the reactive dyes. The obtained rate constants for hydrolysis/methanolysis of the dye show that the change of rate constants of hydrolysis/methanolysis at 130°C, pH 8.0 is similar to that obtained at 90°C, pH 11.0, that is, the methanolysis reactions of the first chlorine atoms in bis(monochloro-s-triazine) reactive dye are high prior to hydrolysis reaction at two temperatures. Meanwhile, both the hydrolysis rates and the methanolysis rates of the second chlorine atoms in bis(monochloro-s-triazine) dye form showed decline after the first chlorine atoms were hydrolyzed, but decreases of the hydrolysis rates were greater, so the methanolysis reactions for the second chlorine atoms were still priority. Similarly, both the hydrolysis rates and the methanolysis rates of the second chlorine atoms in bis(monochloro-s-triazine) dye form show decline after the first chlorine atom was methanolysised, and decrease for the hydrolysis rate was greater, so the methanolysis reaction was still priority. Moreover, rising temperature did not change the rule that methanolysis reaction is always priority in competitive reaction between the dye and the alkali, and the methanol, but higher temperature decreased methanolysis efficiency of the bis(monochloro-s-triazine) reactive dye.3. Because massive low molecule products were found in high-temperature hydrolysis reactions of the bis(monochloro-s-triazine) reactive dye(i.e. C.I. Reactive Red 120), using ultra-high performance liquid chromatography and flight time mass spectrum(UPLC-MS) tested the mass-to-charge ratios of these low molecule products obtained at different hydrolysis time at 130°C. Substances that mass-to-charge ratios are 703.0391, 612.9782, 501.9708 and 218.0676 were detected, confirming that the degradation of the dye with imine bridge group at high temperature in alkali solution is caused by breakage of imine bridge group of the dye. Moreover, the degradation mechanism of the dye was studied, it was found that the hydrolysis reaction of the dye was prior to the degradation reaction; the degradation reaction happened after the bis(monochloro-s-triazine) reactive dye was hydrolyzed to bis(monohydroxy-s-triazine) dye. The position of breakage of bond is the C-N bond formed between carbon atom in triazine and nitrogen atom in p-phenylenediamine when the first degradation happened; the product out of the degradation degraded again at position where C-N bond formed between carbon atom in triazine and nitrogen atom in imine linking group.4. A new dye with propane diamine bridge group and parent dye of C.I. Reactive Red 120 was synthesized and its stability properties at high temperature were contrasted with C.I. Reactive Red 120 with the p-phenylenediamine bridge group. It was found that because of pushing electron effect of propilidene, electron cloud density of carbon atom in s-triazine increased(i.e. electropositivity of the carbon atom decreased), the covalent bond formed between carbon atom in s-triazine and nitrogen atom in p-phenylenediamine bridge group could be not easy to break when it subjected to OH- attacks, so the stability of the dye increased in alkali solution.5. Hydrolysis reactions of reactive dyes(C.I. Reactive Red 120, C.I. Reactive Red 141, C.I. Reactive Red 268, C.I. Reactive Blue 171, C.I. Reactive Blue 198 and the new dye with propane diamine bridge group) fixed on fibers in ranges of 90°C to 130°C and pH 8.0 to 11.0 were studied through testing hydrolysis rates of dyes fixed. Results showed that the hydrolysis rates of the bis(monochloro-s-triazine) reactive dyes fixed increase as hydrolysis temperatures and pH values rise, but the hydrolysis degree of the dyes fixed at high temperatures could be decreased by lowing the pH values of the dye bath. However, a more effective manner for decreasing the hydrolysis rates of the dyes fixed was to optimize molecular structure of the dyes, especially imine group structure.6. Dyeing thermodynamics and kinetics for bis(monochloro-s-triazine) dyes(Reactive Red KE-3B, Reactive blue KE-R and Reactive Red KE-3G) were studied. Comparing with curves of dyeing rates at different temperatures, it was found that dye uptakes at low temperatures(80°C and 90°C) presented increase firstly and later flattened; however, at high temperatures(exceeds 100°C), the dye uptakes increased rapidly to maximum at the beginning of the dyeing and later declined suddenly(appeared a inflection point in curves of dyeing rate), an then rise slowly again until reaching equilibrium. Meanwhile, other characteristic of dyeing thermodynamics and characteristic of dyeing kinetics(including adsorption isotherm, dyeing affinity, diffusion coefficients, the times of half dyeing and dyeing rates) did not change at high temperatures.7. A decomposable liquid alkali consisting of tetraethylammonium hydroxide(TEAH) as an alkaline donor and sodium bicarbonate as an alkaline buffer was designed and applied to high-temperature(130 °C) dyeing of bis(monochloro-s-triazine) reactive dyes under the optimum application condition of the decomposable alkali. Results given phased sampling and testing for two dyes(C.I. Reactive Red 120 and C.I. Reactive Blue 160) showed that the cause that decomposable liquid alkali enhanced high-temperature dyeing effects of the bis(monochloro-s-triazine) reactive dyes was lie in tremendously reducing the hydrolysis of the dye fixed by declining the pH value of dye bath in high-temperature dyeing stage. However, the decomposable liquid alkali could provide an adequate number of alkaline donors to maintain the reaction between the dye and the cellulosic fiber during the low-temperature stage of dyeing, which also was essential for improving high-temperature dyeing effects of the bis(monochloro-s-triazine) reactive dyes.