Some novel azo reactive dyes

The synthesis of some novel azo dyes is described. They have an aldehyde auxochromic group in the dye molecule, and show promise as effective reactive dyes for wool.     

Cellulase digestion of cotton dyed with reactive dyes and analysis of the products by thin layer chromatography

Enzymatic digestion of cotton fibres dyed with reactive dyes produces coloured solutions. These are not true dye extracts but they are nonetheless amenable to separation and analysis by thin layer chromatography.     

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.     

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.     

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.     

Ozone utilisation for discharge printing of reactive dyed cotton

Environmental pollution is one of the major concerns of the textile finishing sector. The reduction or substitution of the harsh chemicals used during dyeing and printing processes is necessary. In this study, the use of ozone for the discharge printing process was examined in order to substitute the use of reductive agent and caustic soda by ozone gas. The reactive dyed cotton samples were wetted by water and some selected solutions at 25%, 40% and 60% pick up were used and subjected to ozone gas treatment. The gas flow rates were 5 and 10 l/min for 5 and 10 min treatment times, respectively. The results were compared with that of conventional discharge printed samples. Colour discharge (%), colour difference (ΔE), strength, washing and rubbing fastness and chemical oxygen demand (COD) values were compared and reported. Colour discharge increased at higher gas flow rates and prolonged treatment times. Although ozone printing could not attain the contour sharpness of conventional discharge printing, the addition of selected chemicals affected colour discharge and the contour sharpness. Strength tests did not show a significant decrease when using ozone treatment. Fastness tests results (washing and rubbing) were slightly higher compared with conventional discharge printed samples. COD values were much lower for ozone treatment compared with conventional discharge printing effluent. Consequently, it was demonstrated that ozone may be an environmentally friendly substitute for discharge printing.     

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.     

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.     

Fading of azo reactive dyes by perspiration and light

The fastness of azo reactive dyes on cellulose in a combined perspiration and light test was investigated, and compared with the results obtained in a conventional light fastness test. Whereas reactive dyes containing an H-or K-acid azo chromophore performed better in the conventional light fastness test, reactive dyes of the J-or γ-acid type exhibited a higher fastness in the combined test. The results suggest that testing under combined perspiration and light conditions involves a photoreduction mechanism, but a photo-oxidation mechanism operates when dyed fabrics fade under light only.     

The effect of reactive dyes upon the uptake and anti bacterial action of poly(hexamethylene biguanide) on cotton. Part 2: Uptake of poly(hexamethylene biguanide) on cotton dyed with β-sulphatoethylsulphonyl reactive dyes

Polyhexamethylene biguanide (PHMB) is a widely used bacteriocide. It is marketed as an aqueous solution of its hydrochloride from which it is readily adsorbed onto cotton, this process depending upon the ability of the cationic PHMB to form electrostatic links with the anionic carboxylate groups present on cotton. The introduction of chemically bound sulphonic acid groups into cotton, which takes place during the process of dyeing with reactive dyes, increases the capacity of cotton to take up PHMB. The saturation levels of PHMB on un-dyed cotton, and cotton dyed individually with a trichromat of warm dyeing dyes, has been measured. Additionally, the effective agent contents of the dyes and their percentage fixation on to the cotton were determined, thus allowing the concentration of sulphonic acid groups present on the cotton to be calculated. From this and knowledge of the saturation value of PHMB on dyed and un-dyed cotton the stoichiometry of the interaction between PHMB and sulphonic acid groups was deduced. For the disulphonated dye, C I Reactive Black 5, each sulphonic acid group appeared to be associated with uptake of an additional 1.12 equiv. of monomeric biguanide unit. For the monosulphonated dyes, C I Reactive Orange 16 and C I Reactive Orange 107, the corresponding values were 1.31.and 1.47, respectively.     

Photochromism of polyurethane cationomers with pendent azo groups

A new polyurethane cationomer with pendent azo groups bounds to quaternary nitrogen atoms has been synthesized by polyaddition reaction between poly(tetramethylene oxide) (PTMO), 4,4′-bibenzyldiisocyanate and N-methyldiethanolamine, followed by quaternization of tertiary nitrogen with 4-(3-chloropropionyloxy)azobenzene. E–Z photoisomerization of azo chromophores by UV irradiation with a high pressure mercury lamp and Z–E thermal relaxation were studied both in solution and film. An azo urethane model and a synthetic mixture of polyurethane cationomer with azobenzene were used for comparison.     

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     

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.     

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.     

Prediction of recipes for cotton cationisation and reactive dyeing to shade match conventionally dyed cotton

Cationisation allows cotton to be dyed with anionic dyestuffs (including anionic pigment dispersions) without the need for salt, and with decreased usage of dye, water, and energy. Appropriate cationisation levels play a part in dyeing properties such as fabric levelness, in fastness properties such as lightfastness, and in the overall cost of the cationisation treatment. The objective of this work is to assess whether it is possible simultaneously to predict a dye recipe and cationisation treatment level for cotton to yield a colourless or nearly colourless dyebath at the completion of the dyeing to match the shade of conventional fibre reactive dyeing of cotton. It has been shown that it is possible to model a cold pad batch cationisation process, relate the colour yield data and cationisation level for individual dyes, and finally predict a dyeing recipe and the required corresponding cationisation treatment to match the shade of conventional fibre reactive dyeing of cotton. The predicted dye recipe and cationisation amount yield colourless or nearly colourless dyebaths at the conclusion of the dyeing process.     

Decolorization and degradation of reactive azo dyes via heterogeneous photocatalytic processes

Reactive dyes are extensively used in textile industry in the last years due to their superior performance, but they are environmentally hazardous and difficult to treat effectively by classical methods. In the present work, the decolorization and degradation of four commercial reactive azo dyes, namely Remazol Red RR, Remazol Yellow RR, Procion Crimson H-exl and Procion Yellow H-exl, were studied using photocatalytic processes (TiO₂/UV and TiO₂/UV/H₂O₂). Decolorization and degradation were found to strongly depend on the system parameters (TiO₂ loading, dye and H₂O₂ initial concentrations, and pH). Decolorization efficiency (%) sharply increases with increasing the TiO₂ loading, especially up to 1 g/L, as well as with decreasing the initial dye concentration from 250 down to 50 mg/L. At pH = 3, a > 90% decolorization of all dyes can be achieved in only 15 min. Addition of H₂O₂ increases the decolorization rates up to an optimum value (97.9% Remazol Red RR decolorization at 12 min irradiation, with a 0.5%w/w initial H₂O₂ concentration and pH = 3). Among the four dyes examined, significant differences in decolorization and degradation rates were revealed, but decolorization and degradation efficiencies up to 100% (in 25 min and 4 h respectively) are possible with proper combinations of the system parameters.     

Equilibrium studies on the adsorption of reactive azo dyes into zeolite

Zeolite was used as a low-cost adsorbent to evaluate its ability to remove color from textile effluents. The zeolit (clinoptilolite) used in this study is a natural clay mineral from the Gbrdes region of Turkey. The adsorption of reactive dyes into zeolite was investigated by a series of batch adsorption experiments. Three reactive dyes (Everzol Black, Everzol Red, Everzol Yellow) were used in laboratory studies. Adsorption test were carried out as a function of solids concentration, conditioning time and dye concentration. The degree of hydrophilicity was found to play an important role in the uptake of reactive dyes. The adsorption results indicated that natural zeolite has a limited adsorption capacity for reactive dyes but can be distinctly improved by modifying its surfaces with quaternary amines. A comparison of natural and modified zeolites at 5% solids concentration indicated that, while the adsorption densities of dyes with natural zeolite yielded negative or slightly positive values, those with modified zeolite gave adsorption densities in the range of 2.9 to 7.6 mg/g.     

The application of cationic fixing agents to cotton dyed with direct dyes under different pH conditions

The effect of application pH on the effectiveness of the conventional cationic fixing agents Matexil FC-ER and Fixogene CXF in improving the wash fastness of the commercial direct dyes CI Direct Red 89, CI Direct Yellow 106 and CI Direct Blue 85 on cotton has been investigated. While the recommended neutral pH application resulted in improved fastness of the dyeings to the ISOC06/C2 wash fastness test, wash fastness was noticeably better when the fixing agents were applied under alkaline conditions.     

Photofading of azo dyes: a theoretical study

The light fastness of a number of azo dyes has been investigated using all-valence molecular orbital methods, AM1 and PM3. The results of molecular orbital calculations are used to obtain both highest occupied molecular orbital and lowest unoccupied molecular orbital frontier electron density, which, respectively, can account for the propensity of the electrophilic and nucleophilic attack at a particular atom in a molecule. The highest occupied molecular orbital and lowest unoccupied molecular orbital superdelocalisability have also been obtained to explain the order of light fastness values in different dyes of a particular series. In addition, attempts have been made to correlate the light fastness values with the difference in energy of the highest occupied molecular orbital of the dye and the lowest unoccupied molecular orbital of the singlet oxygen.