Radio-frequency-assisted fixation of reactive dyes by pad-batch application

This study was undertaken in an effort to use radio-frequency energy to improve the level of fixation of reactive dyes on cotton in pad-batch dyeing. The successful application of statistical experimental design strategies for the development and optimisation of a new dye application method is described. Key process variables were identified and optimised to maximise dye fixation. Heating of the batch with radio-frequency energy during the batching stage greatly accelerated the rate of fixation. Fixation levels achieved using optimised radio-frequency-assisted methods were approximately equivalent to those achieved in conventional pad-batch dyeing.     

Synthesis and application to cotton of a polymeric black colorant prepared by grafting of reactive dyes to polyvinylamine

A novel polymeric black dye was synthesised by grafting yellow, orange, red, and blue reactive dyes onto polyvinylamine. Such a polymeric black dye takes the onus away from dyers to worry about the compatibility of individual dyes. The polymeric black dye was characterised by Fourier transform infrared, ultraviolet‐visible, and nuclear magnetic resonance spectroscopy. The absorption of the polymeric black dye in aqueous solution was nearly constant across the wavelength range 400–700 nm. Compared with a black mixture of reactive dyes with low fixation on cotton, which was prepared by mixing yellow, orange, red, and blue reactive dyes, the polymeric black dye reached 99% fixation on cotton through the use of a crosslinking agent. The colorimetric properties of cotton dyed with the polymeric black dye and with the black mixture of reactive dyes showed that better blackness can be obtained by using the polymeric black dye. Analysis of the thermal stability and penetration ability of the polymeric black dye showed that the polymeric dye has high stability in the application and a uniform distributution in the cotton fabric.     

Foam properties and application in dyeing cotton fabrics with reactive dyes

The foam dyeing of cotton fabric with CI Reactive Red 120 has been studied as a low‐add‐on technology. The foamability of different types of foaming agent and the stability of foam stabilisers were compared. Factors influencing foam dyeing, including wet pick‐up, fixation agent, foam stabiliser, and blow ratio, were evaluated by colour strength and dye fixation rate. Wet pick‐up, fixation agent, and foam stabiliser were found to be the main factors in the foam dyeing process. The comparative build‐up properties, dyeing properties, and total consumption between foam dyeing and conventional dyeing were assessed. The results indicate that, in foam dyeing, the dyestuff has a better build‐up property, the dyed fabric has excellent wash and rub fastness, and large amounts of water and energy are saved. Moreover, foam dyeing requires smaller dosages of chemical agents and reduces the difficulty of effluent treatment.     

Neutral-fixing reactive dyes for cotton.

Research into a new type of reactive dye based on the monochlorotriazine group is described. Reactive dyes of the 3-carboxypyridino-1,3,5-triazine type have been investigated, with a nicotinic acid leaving group, having high stability and fixation efficiency. Dyes of this type react with cellulose in a neutral bath, so widening the scope of reactive dyeing. A classification scheme for reactive dyes is outlined.     

Neutral-fixing reactive dyes for cotton. Part 1 —synthesis and application of quaternised S-triazinyl reactive dyes

A number of different tertiary amines have been employed to prepare the corresponding quaternised triazines from a selected monochloro-s-triazine reactive dye. Preparation conditions have been established along with suitable analytical methods. The reactivity of the quaternised dyes with cellulose has been determined, special attention being paid to neutral fixation at high temperatures (100°C). Good neutral fixation was achieved with all the tertiary amine derivatives studied. In the case of the nicotinamide derivative an anomalous hydrolysis reaction involving ring opening was noted; this reaction led to the formation of aminotriazine rather than the expected hydroxytriazine.     

Printing of cationised cotton with reactive dyes

The printing properties of cationised cotton that had been pretreated with 2,3-epoxypropyltrimethylammonium chloride were examined. Fixation (steaming) time, colour yields, colorimetric properties, fastness properties, staining of the white grounds and penetration behaviour were evaluated for a number of reactive dyes with cationised cotton fabrics. The cationisation of cotton was found to be very effective in reducing steaming times and washing off processes, and in increasing colour yield. Fastness and other properties of the printings are also discussed.     

The dyeing of cotton with phosphonic reactive dyes in alcohols

The poor fixation achieved with phosphonated reactive dyes on cotton in practice, particularly in printing, has prompted a study of the effect of reaction conditions and the use of different diimides to achieve fixation. It has been possible to achieve as much as 95% fixation with a typical dye under suitable application conditions, where decomposition of the diimide can be minimised.     

Continuous dyeing of cationised cotton with reactive dyes

Cotton fabrics pretreated with cationic starch have been dyed with reactive dyes by a continuous dyeing method and the pretreatment conditions influencing dyeability of the treated cotton investigated. Cationised cotton has been found to give level dyeing without the presence of salt and dye fixation is improved compared with untreated cotton. The dyeings show good wash and rub fastness.     

Electrochemical oxidation of reactive dyes: method validation and application

Electrochemical oxidation is a very effective technique for wastewater processing and, in the textile industry, it can be employed to remove colour from residual dyeing and washing liquors. In previous studies, the main factors were established for the control of the electrochemical removal of reactive dyes from textile wastewater. Mathematical models were proposed for the decolorisation of these dyes and for the electrical consumption. In the present work, these models are analysed and a three-step methodology is established in order to determine whether a dye can be removed from wastewater by electrochemical treatment. This methodology is applied and verified on a further four reactive dyes. The mathematical models are also employed to evaluate the colour removal from textile wastewater samples containing reactive dyes.     

Photochromism of yellow azo dyes: a specific phenomenon of cotton dyed with reactive dyes

A method that is more sensitive than the ISO standard procedure for the detection and assessment of photochromism has been developed using a colour measuring device. Using this method the photochromism of various yellow azo reactive dyes applied to cotton has been studied. This has shown that azo dyes that can form a hydrazone tautomer tend not to be photochromic. In particular for pyrazole and hydroxynaphthalene azo dyes, the colour change is too small to be perceived by the human eye. Furthermore photochromism decreases with increasing size of the aromatic moieties attached to the azo group, as well as with the increasing number of substituents located ortho to the azo linkage. Finally the photochromism of dyeings with the golden yellow chromophore of structure IV was reduced when they were finished with certain Knittex brands.     

Dyeing cotton with reactive dyes under neutral conditions

This paper describes a new method to dye cotton with selected reactive dyes by long-liquor – or so-called 'exhaustion'– processes under neutral conditions. Particularly promising results were obtained with reactive dyes containing free vinyl sulphone residues. Although there are dyes on the market that contain free vinyl sulphone groups, for example, the Novacron C (Huntsman) range of dyes, many of this class contain 'blocked' vinyl sulphone residues; examples include sulphatoethylsulphone or chloroethylsulphone precursor groups, and these may be preactivated to the highly reactive vinyl sulphone form simply by a mild alkali treatment. After this activation, neutral, long-liquor dyeings can be carried out at the boil in the presence of electrolyte. This new dyeing method gave very good results in terms of overall fixation efficiency values, without the need for alkali additions.     

The use of reflectance measurements in the determination of fixation of reactive dyes to cotton

The utility of the Kubelka–Munk equation for determining the fixation of reactive dyes to cotton has been assessed. Large K / S values are not linearly related to dye concentration on fabric and thus give an inaccurate assessment of fixed dye. If lower values of K / S are selected, by measuring at a suitable wavelength, a linear relationship exists with the concentration of dye present, even at very heavy depths of shade. Thus, by judicious choice of wavelength, K / S values can provide an accurate and convenient method for the assessment of dye on fabric, provided that a reference fabric sample, with a known concentration of the same dye, is available as a standard for comparison. Significant implications are then revealed for construction scalable models of opaque medium reflectance that are homogeneously linear over wavelength with respect to colorant concentration change. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 117–121, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20189     

Urea/alkali-free printing of cotton with reactive dyes

Urea reduction or elimination in reactive dye print pastes is of ecological interest. Sodium edetate is presented as a complete substitution of urea in the conventional print paste of reactive dyes, namely CI Remazol Black B and Remazol Brilliant Orange 3R using a constant amount of sodium alginate as the thickening agent. Three different print pastes containing urea/NaHCO₃, sodium edetate/NaHCO₃ and sodium edetate were thoroughly investigated. Different factors that may affect the printability of cotton, such as the concentrations of sodium edetate, urea, dye, absence or presence of alkali and steaming time in the prints obtained were evaluated with respect to the dye fixation, colour strength, dye penetration, levelling and the fastness properties. Excellent to good fastness was obtained for all samples irrespective of the print paste used.     

The accessibility of cotton to anionic dyes

Adsorption isotherms have been obtained for two direct dyes on unmercerised cotton and viscose yarns at the boil in the presence of sodium chloride. Both dyes, CI Direct Red 81 and CI Direct Green 26, show evidence of monomolecular layer adsorption. Controlled acid hydrolysis of cotton was carried out in order to remove non-crystalline cellulose, and dye sorption values were obtained for the residues. Accessible surface areas have been calculated from the saturation values obtained from the reciprocal plots of the adsorption data. The results are interpreted in terms of a crystalline fibril model of the cotton fibre.     

Technological evaluation of reactive cyclodextrin in cotton printing with reactive and natural dyes

The chemical modification of cotton fabric with reactive cyclodextrin (R‐CD) at different concentrations was carried out to enhance the printability of cotton fabric. The extent of the modification reaction was expressed as %N. Reactive and natural dyes were used to print cotton fabric before and after modification. Printing pastes were applied immediately after preparation or after 24 h of storage. Printing fixation was performed through either steaming or thermal treatment. The effect of the incorporation of R‐CD in the printing paste of unmodified cotton was also studied. The results reveal that the extent of the modification reaction increased with increasing R‐CD concentration and so did the color strength (K/S) of the printed sample regardless of the dye used. The results also revealed that K/S of the R‐CD modified cottons were higher than that of the corresponding unmodified samples regardless of the method of fixation or the time elapsed before printing. On the other hand, the incorporation of R‐CD in the printing pastes of reactive dyes, namely, Cibacron Brown 6R‐P or Remazol Brilliant Red GG, had adverse effects, most probability due to the (a) increasing viscosity of the paste and/or (b) interaction of the reactive dye with R‐CD hydroxyls. The opposite held true when a natural dye was used. Further, the incorporation of R‐CD in the printing pastes had no effect on the rheological type of the pastes or the on overall fastness properties of the prints. Nevertheless, such an incorporation of R‐CD was accompanied by a remarkable increase in the magnitude of the apparent viscosity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 338–347, 2006     

Anchoring β-cyclodextrin to retain fragrances on cotton by means of heterobifunctional reactive dyes

Cyclodextrins are cyclic oligosaccharides which are able to form complexes with a wide range of organic compounds, including fragrance oils. As a result of the complexation, the vapour pressure of the volatile substance is reduced and its release is better controlled. To achieve this, β-cyclodextrin can be anchored to cellulose by means of a chemical linkage provided by heterobifunctional reactive dyes.     

Physico-chemical modelling of the dyeing of cotton with reactive dyes

Over the past decades a great deal of research effort has been devoted to understanding the physico-chemical mechanism of the dyeing of cotton with reactive dyes. However, the use of physico-chemical models has been almost exclusively restricted to research laboratories due to the simplifying assumptions used. A more practical model has now been developed and is intended to allow dyeing recipes and the process parameters used in bulk production to be optimised. The model is additionally able to quantify the effect of non-controllable variables on overall dyeing efficiency.     

Selecting reactive dyes for all-in dyeing of polyester/ cotton blends

As a preliminary study to an investigation of the feasibility of dyeing polyester/cotton blend by an all-in process using a pH-shift method, we have investigated the suitability of three types of conventional reactive dyes by considering the effects of pH and temperature on their hydrolysis and fixation behaviour. Monochlorotriazine, vinyl sulphone and bifunctional high exhaustion dyes were assessed but only the bifunctional reactive dye gave acceptable colour yield under the conditions likely to be employed during such a dyeing process.     

A significant approach to dye cotton in supercritical carbon dioxide with fluorotriazine reactive dyes

A series of fluorotriazine reactive dyes have been synthesized and applied to dye cotton in supercritical carbon dioxide (scCO₂) with good dyeing results. The pieces of cotton to be dyed were previously presoaked in a protic solvent and cosolvents were applied during dyeing. The colour strength of the dyeings was evaluated by K/S measurements. The K/S values achieved on cotton dyed were up to 35.8 ± 4.2. Even after the cotton was subjected to a Shoxlet extraction at 358 K for 1 h, a maximum K/S value of 20.2 ± 1.8 was measured. The percentage of dye molecules chemically fixed to the cotton was on average 85%. The excellent reactivity of fluorotriazines allowed a reduction of 3 h on the dyeing time. It is noticeable that a dye concentration of 10% on weight of the fibre (owf) can be applied to dye cotton with fluorotriazines, since no damage of the cotton fibres occurred, as observed for the chlorotriazines at this high dye concentration.Dyes with fluorotriazine as reactive group were found to be the most preferable dyes for dyeing cotton in scCO₂, as they were able to exceed the limitation of the reaction with the cotton.     

Adsorption of dyes to cotton and inhibition by polymers

This paper addresses some key factors that control the transfer of dyes between garments during detergency. It is shown that adsorption of a series of substituted arylazo-2-naphthol dyes to cotton under simulated detergency conditions is influenced by the log P fragment value of the dye substituent; this suggests that hydrophobic interactions make an important contribution to the binding free energy. The comparative effectiveness of nonionic, zwitterionic and cationic polymers in inhibiting adsorption of dye to cotton was also investigated. Increase in polymer concentration reduces dye adsorption to cotton; increase in polymer molecular weight at constant polymer concentration also inhibits dye adsorption up to a molecular weight of ca. 20000, above which there is no further change. Anionic surfactants reduce the efficacy of polymers by displacing dyes from polymers. Surprisingly, certain dyes become relocated in polymer/surfactant complexes; binding is much more effective than in corresponding surfactant micelles.