| Reactive dyes become the main dye for cotton due to their excellent color fastness to laundering, acceptable prices, wide color gamut and brightness of shade. But in the dyeing process, it’s necessary to add a large amount of inorganic salts to promote dyeing, which resulted in emissions of salty wastewater. Based on salt pollution, the biomass material, chitosan(CS) was as raw materials to synthesize a serial of cationic modifiers for cotton fabric with the aims to reduce the amount of salt usage and optimize the dyeing process.Firstly, several preparation methods were used to synthesize three kinds of cationic quaternized chitosans, named trimethyl ammonium chloride chitosan(Quat-CS1), N-trimethyl ammonium chloride chitosan(Quat-CS2) and N-hydroxypropyl ammonium chloride chitosan(Quat-CS3). Then CS and quaternized chitosan were applied in the dyeing of cotton with reactive dye. The influences on the dye-uptake from salt dosage, alkali dosage or dyeing time were discussed and the adsorption mechanisms of cotton pretreated were also studied. The result showed that the obtained quaternized chitosans can be used as low or free salt dyeing auxiliaries. The dyeability-improvement of quaternized chitosans was higher than CS, and among of which, Quat-CS3 was the best. Without the addition of salts, both the adsorption-rate and the equilibrium-exhaustion of cotton pretreated with Quat-CS3 were higher than that with Quat-CS1 or Quat-CS2. The adsorption mechanism of cotton pretreated with quaternized chitosan followed by the Langmuir model, while that pretreated with CS followed by the Freundlich model.The synthesis and dyeing conditions of Quat-CS3 were furtherly optimized by orthogonal experiments, which could suit the three different reactive dyes(red, yellow and blue). The optimum synthesis conditions were: reaction temperature at 90 ℃, reaction time at 24 h, mass ratio of CS/GTA at 1:8, and the solvent volume at 200 m L. And the optimum dyeing process was: modified dosage at 0.5 g/L, modifying time at 20 min, modifying temperature at 60 ℃, dyeing time at 20 min. The results showed that the optimum dyeing process was benefit with its short working time, less-salt usage and low-energy consumption. In the optimum dyeing conditions, all the dyeing-rates of the three reactive dyes are more than 78%. However, their wet-fastness was only grade 2-3, which need to be improved.In order to improve the wet-fastness of cotton fabrics prepared with Quat-CS3, the reactive quaternized chitosans were synthesized by grafting reactive groups and the dyeability-improvement were also investigated. IR spectra showed that cyanuric chloride or methylolacrylamide were successfully grafted into Quat-CS3. The results showed that the optimum dyeing processes of red, yellow and blue reactive dyes were obtained by the orthogonal experiments in a small bath ratio, short process and salt-free dyeing process; under the optimum conditions, the dyeing effects of cotton fabric modified with reactive quaternized chitosan were better than that of unmodified, among which the wet-fastness was improved by 1-2 level.Several methods were used to modify the structure of chitosan molecular, and then five kinds of chitosan derivatives were synthesized. The systematic research provideda certain theoretical basis for molecular modification of chitosan. Meanwhile, an optimum dyeing process was developed with low salt, short work cycle and low consumption, which provided the use of reactive dyes with certain practical value.
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