Salt-free Dyeing Research Articles

Salt-free dyeability of thiourea grafted cotton fabric

In this study salt-free dyeing cotton fabric was achieved by grafting thiourea to cotton fibers, where the thiourea grafted cotton fabric (TUGCF) was prepared by epoxidizing cotton fibers with epichlorohydrin in water and subsequently grafting in aqueous solution of thiourea. Fourier transform infrared spectra (FTIR) and XPS of the TUGCF indicated that a great amount of epoxy groups from the epoxidized cotton fibers reacted with amino groups from thiourea. The TUGCF fabric prepared at the optimum condition and subsequently dyed with reactive dyes in the absence of salt displayed significantly enhanced color strength, showing better dyeing properties when compared with the untreated cotton fabric dyed with conventional methods, in terms of washing fastness, rubbing fastness, and levelness. It was found that the dyeing performance of Reactive Red B-3BF followed a Langmuir-type adsorption curve when used to salt-free dye the TUGCF.

Application of Tertiary Amine Cationic Polyacrylamide with High Cationic Degree in Salt-free Dyeing of Reactive Dyes

Tertiary amine cationic polyacrylamide with high cationization degree was used as a new cationic agent to pretreat cotton with dip-pad-bake method. The obtained cationic cotton was dyed with reactive dyes in the absence of electrolyte. The effects of the characteristics of the cationic agent and the pretreatment conditions on dyeability of reactive dye were investigated. The results showed that the fixation and K/ S values of the reactive dyes on the cationic cotton were improved compared with those on the untreated one in the presence of salt. Tests on fastness properties of the dyed cotton and fabric quality of the pretreated cotton were carried out and the results showed that wash and rub fastness of the salt-free dyeing were both satisfactory. And anti-crease property, tensile and tear strength, and handling of the cationic cotton were also good compared with that of the untreated one.

The Application of Water-soluble and Reactive Chitosan on Antimicrobial Activity and Salt-free Dyeing of Reactive Dyes

A novel chitosan derivative, O-acrylamidomethyl-HTCC (NMA-HTCC) was synthesized in two steps. First, N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride (HTCC) was prepared by introducing 2,3-epoxy propane trimethlyl ammonium chloride(GTA) on the amino groups of chitosan. HTCC was further modified by reacting with N-methylolacrylamide (NMA) on the primary alcohol groups (C-6) on the chitosan. The effect of modified chitosan on the dyeing properties of cotton fabric was studied by measuring the dye uptake and K/S values of the treated substrates with different treating processes under salt-free conditions. The antimicrobial activity of modified chitosan against Escherichia coli and the durability of antimicrobial activity was assessed using percentage reduction rate of the bacterium with different treating processes. The results indicate that modified chitosan treated cotton fabric shows increased dye uptake, K/S values and fastness, and its antimicrobial activity and durability are much better than chitosan treated cotton fabric.

Preparation of cationic cotton with two-bath pad-bake process and its application in salt-free dyeing

Cationic cotton was prepared by a designed two-bath pad-bake process with 3-chloro-2-hydroxypropyltrimethylammonium chloride as cationizing reagent to realize recycle utilization of the reagent and continuous processing of cationization. Experiments showed that 8.0% (o.w.bath) of the reagent, 1:1 of molar ratio of sodium hydroxide to the reagent, 60 °C and 6 min of baking temperature and time were selected for cationization and the obtained cationic cotton was suitable for application in salt-free reactive dyeing. The structures of both the untreated and cationic fibers were investigated by X-ray diffraction and scanning electronic microscopy. Higher dye utilization and color yields could be realized on the cationic cotton than that on the untreated one in the conventional dyeing. Levelness dyeing and good fastness properties of the dyes on the cationic fabrics were obtained. Besides, colorimetric properties and mechanical strength of the dyed fabrics were both evaluated to show applicability of this preparation process of cationic cotton.

HBP-NH 2 grafted cotton fiber: Preparation and salt-free dyeing properties

In order to achieve salt-free dyeing on cotton fiber with reactive dyes, an amino-terminated hyperbranched polymer (HBP-NH 2) grafted cotton fiber (HGCF) was prepared by the oxidation of cotton fiber with sodium periodate in water and subsequent grafted with an aqueous solution of HBP-NH 2. Fourier transform infrared spectrophotometry (FTIR) of the HGCF indicated that all aldehyde groups of the oxidized cotton fiber have reacted with amino groups of the HBP-NH 2. As a result, the HGCF fabrics prepared under the optimum conditions displayed markedly enhanced colour strength when dyed with reactive dyes using salt-free dyeing. The washing fastness, rubbing fastness and levelling properties of the dyed HGCF fabrics were also good compared with those obtained by conventional dyeing. The zeta-potential of the HGCF in liquid phase was tested and found to be positive at pHs lower than 6.5. The dyeing behaviour of Reactive Brilliant Yellow A-4GLN on the HGCF was found to follow a Langmuir-type adsorption curve.

Synthesis of cationic hydrolyzed starch with high DS by dry process and use in salt-free dyeing

Cationic hydrolyzed starch was prepared by hydrolyzed maize starch with 2,3-epoxypropyltrimethyl ammonium chloride by dry process. Experiments showed that 80 °C, 1 h, 0.1:1 of molar ratio of sodium hydroxide to cationizing reagent were suitable for cationization, and high degree of substitution of cationic hydrolyzed starch was obtained. The structures of the hydrolyzed maize starch and cationic hydrolyzed starch were characterized by IR spectroscopy, scanning electronic microscopy and X-ray diffraction. The synthesized cationic hydrolyzed starch was employed in salt-free dyeing of reactive dyes. It showed that high dye fixation and level dyeing were obtained by pretreating cotton with the cationic hydrolyzed starch with low viscosity and high DS. Besides, wash fastness and rub fastness were not affected. The highest dye fixation in salt-free dyeing is higher than that of conventional dyeing by 20.3%, 0.9% and 18.4% for C.I. Reactive Red 2, C.I. Reactive Blue 19 and C.I. Reactive Yellow 145, respectively.

Pretreatment of cotton with poly(vinylamine chloride) for salt‐free dyeing with reactive dyes

Poly(vinylamine chloride) has been investigated as a pretreatment for the salt-free dyeing of cotton with reactive dyes. Dye fixation was found to be much higher than by conventional dyeing without pretreatment, even in the presence of a large amount of salt. The influence of pretreatment conditions on dye fixation, such as pad–bake variables and the concentration of poly(vinylamine chloride), has been studied. The dyeing behaviour of CI Reactive Red 2 on pretreated cotton was examined and found to follow a Langmuir-type adsorption curve. Dyed cotton pretreated with poly(vinylamine chloride) showed excellent wash fastness and good rub fastness. It is concluded that poly(vinylamine chloride) is effective as a pretreatment for salt-free dyeing with reactive dyes.