pH Dependent redox behaviour of Alizarin Red S (1,2-dihydroxy-9,10-anthraquinone-3-sulfonate) – Cyclic voltammetry in presence of dispersed vat dye

The redox chemistry of Alizarin Red S (1,2-dihydroxy-9,10-anthraquinone-3-sulfonate) was studied as function of pH by photometry, potentiometric titration and cyclic voltammetry. Dependent upon solution pH three species of the oxidised form of Alizarin Red S are present. Electrochemical reduction of the anthraquinone group leads to 1,2,9,10-tetrahydroxy-anthracene-3-sulfonate. The four phenolic hydroxyl groups dissociate with increasing pH value, above pH 12 a tetra anion is the main species in solution. Cyclic voltammetry experiments in unbuffered solution indicate that the overall cathodic reduction contains electron transfer and pH-dependent protonation reactions. Above pH 12 dispersed Vat Yellow 1 could be reduced by indirect cathodic electron transfer using the fully deprotonated system as reversible redox couple. In cyclic voltammetry a reduction potential of (E_p)_d = −900 mV (vs. Ag/AgCl/3 M KCl) was observed, which is sufficiently negative to reduce Vat Yellow 1. No indication for an indirect cathodic reduction of Vat Yellow 46 could be registered.     

pH Dependent redox behaviour of Alizarin Red S (1,2-dihydroxy-9,10-anthraquinone-3-sulfonate) - Cyclic voltammetry in presence of dispersed vat dye

The redox chemistry of Alizarin Red S (1,2-dihydroxy-9,10-anthraquinone-3-sulfonate) was studied as function of pH by photometry, potentiometric titration and cyclic voltammetry. Dependent upon solution pH three species of the oxidised form of Alizarin Red S are present. Electrochemical reduction of the anthraquinone group leads to 1,2,9,10-tetrahydroxy-anthracene-3-sulfonate. The four phenolic hydroxyl groups dissociate with increasing pH value, above pH 12 a tetra anion is the main species in solution. Cyclic voltammetry experiments in unbuffered solution indicate that the overall cathodic reduction contains electron transfer and pH-dependent protonation reactions. Above pH 12 dispersed Vat Yellow 1 could be reduced by indirect cathodic electron transfer using the fully deprotonated system as reversible redox couple. In cyclic voltammetry a reduction potential of (E_p)_d = −900 mV (vs. Ag/AgCl/3 M KCl) was observed, which is sufficiently negative to reduce Vat Yellow 1. No indication for an indirect cathodic reduction of Vat Yellow 46 could be registered.     

Reuse of spent dyebath following decolorisation with ozone

Spent reactive dyebaths were decolorised by treatment with ozone and reused in the bleaching, whitening and dyeing of two textile substrates. The study shows that the reuse of a spent dyebath is possible with little modification to the standard processes for dyeing cotton with reactive dyes, provided that the pH of the treated dyebath is adjusted. Moreover, the cycle of decolorisation and reuse was successfully repeated. Renovated reactive dyebaths were also reused for bleaching cotton fabric with hydrogen peroxide, whitening with optical brightener and dyeing polyester fabric with disperse dyes. The whiteness index of bleached and whitened cotton was comparable to that of the same fabric given a control treatment with fresh baths. Likewise, there was a negligible colour difference between polyester dyed using liquor from a spent reactive dyebath and the same fabric dyed in a new bath.     

The effect of reactive dyes on damage in wool dyeing

This paper demonstrates that reactive dyes exert a significant fibre–protective effect when dyeing wool fabric; this effect may be measured, in a reproducible manner, using the wet–burst strength test. The effect of dyebath pH, dye concentration, dyebath temperature and dyeing time on wool can thus be evaluated. The magnitude of the above protective effect has been compared with that achieved using commercially available fibre–protective agents. It is concluded that reactive dyes are significantly more effective than the latter agents when employed in medium to full depths. It is proposed that the unusual protective effect afforded by reactive dyes is related to the following factors. Reactive dyes readily react with sulphur nucleophiles, thus inhibiting thiol–disulphide interchange reactions and thereby significantly interfering with the level of set produced in a boiling dyebath. Reactive dyes react preferentially with non–keratinous proteins in the intercellular cement and the endocuticle thus reducing their tendency to hydrolyse and to partially dissolve in the hot aqueous dyebath.     

Investigation of the improved dyeability of cationised cotton via photografting with UV active cationic monomers

In this study cotton fabric was photografted with cationic monomers using UV radiation. The dyeability of cationised cotton, in the absence of salt, with three classes of dye (direct, reactive and sulphur dyes) was significantly improved due to the increased ionic attraction between the dyes and the cationic cotton. The colour fastness of the cationised fabric was similar or better than that of the untreated fabric. In addition, when cationised, crosslinked crease-resist cotton also showed improved dyeability, in the absence of salt, to direct dyes.     

Synthesis of reactive disperse dyes containing halogenated acetamide group for dyeing cotton fabric in supercritical carbon dioxide

A series of reactive disperse dyes incorporating halogenated acetamide group were synthesized and applied to dye cotton fabric in supercritical carbon dioxide (scCO₂). Dyeing experiments were conducted in scCO₂ with dye concentration of 0.5% owf (% on weight of cotton fabric), varying from 80 to 120 °C, for 1–3 h at a constant pressure of 200 bar. The results showed that the color strength of dyed cotton fabric increased favorably when increasing temperature and time. The color characteristics were studied as well in terms of the reflectance spectra. And the color fastness to washing and rubbing were also reasonably good.     

Electrochemical reduction of CI sulphur black 1—correlation between electrochemical parameters and colour depth in exhaust dyeing

Direct cathodic reduction of oxidised CI Sulphur Black 1 was achieved by means of a multi-cathode electrolyser at cell currents of 0.9–1.5 A. The redox potential in the catholyte decreased from initially −250 to −533 mV as a function of charge flow. The catholyte also served as dyebath for cotton fabric samples. Colour depth was characterised by Kubelka–Munk value K/S and CIELab-coordinates and was studied as function of charge flow and redox potential in the catholyte. Direct correlation between redox potential and colour depth of the dyed samples was observed. Electrochemical reduction permits steering of catholyte/dyebath potential by adjustment of cell current and thus permits direct control of the dyeing process by electrochemical methods.     

Nanofiltration for the possible reuse of water and recovery of sodium chloride salt from textile effluent

During the reactive dyeing of cotton, salts such as sodium chloride (NaCl) are placed in a dyebath to aid the exhaustion of various dyes onto the fabric while bases are added to raise the pH from around neutral to pH 11 to achieve fixation. Afterwards, the used dyebath solution, called dyebath spent liquor, is discharged with almost all the salts and bases added as well as unfixed dyes. Consequently, many raw materials are lost in the waste stream ending up in the environment as pollutants. In this study possibilities of reusing the water and salts of dyebaths were investigated using a nanofiltration membrane. When the NaCl concentration in the spent liquor was increased from 10 to 80 g/L, the NaCl rejection by the membrane was found to decrease initially; however, the NaCl rejection increased over time, which was not expected. The aggregation of dye was also studied and found to decrease in the concentrate when the salt concentration was increased. This information is useful for the textile industry in evaluating the treated water quality for the purpose of reuse.     

Electrocarboxylation of 2-methylhalogen-9,10-anthraquinones

Herein we propose a new synthetic route for the production of 9,10-anthraquinone-2-ethanoic acid (AQEA) by electrocarboxylation of 9,10-anthraquinone-2-bromo-methyl (BrMAQ) or 9,10-anthraquinone-2-chloro-methyl (ClMAQ). Electrocarboxylation of anthraquinones appears as an alternative for synthesizing their respective carboxylic acids. Electrosyntheses were carried out using N,N-dimethylformamide (DMF) as solvent, NaClO₄ as electrolyte and metallic magnesium as sacrificial anode. One of electrolysis products was AQEA, which was isolated, purified and then analysed by IR, RMN and high performance liquid chromatography (HPLC). Electrocarboxylation selectivity to AQEA ranged on average from 32 to 40% using ClMAQ and BrMAQ, respectively.     

The reduction of dispersed indigo by cathodically formed 1,2,4-trihydroxynaphthalene

The indirect cathodic reduction of the vat dye indigo (C.I. Vat Blue 1) by cathodically reduced Lawsone (2-hydroxy-1,4-naphthoquinone; C.I. Natural Orange 6) was studied in aq. solution at different pH values. Cyclic voltammetry and spectroelectrochemistry were used to investigate the electrochemical behavior of 2-hydroxy-1,4-naphthoquinone at a hanging mercury drop electrode. The cathodic peak potential (E_p)_d measured at 0.1 mM lawsone solution at a scan rate of 50 mV s^?1 changed from ?425 mV at pH 7, to ?730 mV at pH 11.5 and ?750 mV at pH 13 (vs. Ag/AgCl, 3 M KCl). Particularly at pH values of 8–9 and 11.5–13 voltammograms indicated successful, indirect cathodic reduction of the dye in which the cathodically reduced 2-hydroxy-1,4-naphthoquinone acted as soluble mediator. The linear relationship obtained for (I_p)_d vs. v^1/2 is indicative of a diffusion-controlled electrode reaction mechanism. In the presence of dispersed indigo, the overall cathode reaction is similar to the E_cat process with continuous regeneration of the electroactive species. Spectrochemical experiments were used to prove the indirect cathodic reaction of dispersed vat dyes by 2-hydroxy-1,4-naphthoquinone.     

Process of dyeability modification and bleaching of cotton in a single bath

Graft polymerisation of the cationic monomer, methacryloylaminopropyltrimethylammonium chloride (MAPTAC), onto scoured cellulose was carried out in the bleaching process, aiming at modifying the fibre using a single bath. The extent of MAPTAC fixation on cellulose was measured. The bleaching performance of hydrogen peroxide in the presence of the modifying agent was found to be slightly reduced. The modified bleached cotton fabric was then dyed with a commercial reactive dye in the absence of salt. The dye uptake and colour strength of the modified fabric was markedly increased with an increase in the concentration of MAPTAC. This was attributed to the presence of the cationic groups of the MAPTAC which played a crucial role in attracting the anionic dyes from the dyebath. The results suggest that the dyeing properties of the modified fabric are closely dependent on the efficiency of MAPTAC fixation on cellulose during concurrent modifying and bleaching of cotton.     

Investigation into the effect of a plant‐derived stabiliser on the light and wash fastness of sulphur‐dyed cotton and nylon fabrics

In this study, cotton fabric and nylon fabric were dyed with a range of commercial sulphur dyes and the light and wash fastness of the coloured fabrics was investigated. The effect of after‐treating the coloured cotton and nylon fabrics with a tannin‐based commercial product, Bayprotect Cl, in the presence or absence of sodium sulphate in the treatment bath, was found to significantly improve the light fastness of the sulphur‐dyed cotton, and the photoprotective effect was partially stable to ISO 105‐C06 washing. In addition, the tannin‐based after‐treatment also improved the colour stability of the dyed fabrics to the perborate‐based ISO 105‐C06 washing. The possible mechanisms for the improved fastness properties are also discussed. The application of sulphur dyes to nylon is potentially commercially useful but has been limited because of the reported poor light fastness of the dyeings. The photoprotective effect of the tannin‐based after‐treatment was investigated with a view to providing the necessary commercial performance. However, it was established that on this fibre, the light fastness improvement was marginal, and the associated wash fastness to oxidative bleach‐based ISO 105‐C06 washing was limited.     

Maleic anhydride based copolymer dispersions for surface modification of polar substrates

In this article, we report the modification of poly(styrene-alt-maleic anhydride) (PSMA) with monofunctional amine-terminated poly(dimethyl siloxane) (PDMS–NH₂) by thermal imidization, followed by the preparation and characterization of a surfactant-free artificial latex thereof and application of this latex onto cotton fabric. The imidization reaction was monitored by NMR and attenuated total reflection Fourier transform infrared (ATR–FTIR) spectroscopy. 1,2-Cyclohexyldicarboxylic anhydride was chosen as a model compound for the PSMA copolymer; this allowed a more detailed characterization by NMR and ATR–FTIR spectroscopy. After the PSMA/PDMS–NH₂ imidization reached completion, a fraction of the anhydrides were ammonolyzed. In this way, a self-emulsifying latex with an average particle diameter of approximately 145 nm and a ζ potential of −56 mV was obtained. It was found that the PDMS-modified PSMA latex in which 30 mol% of the initial amount of anhydride groups were previously imidized by using PDMS-NH₂ and a fraction of the anhydrides were ammonolyzed with 0.3 eq. of NH₃ (PSMA30) was stable in the pH range 4–10. The water contact angle values of the latex-coated cotton textile fabric indicated a hydrophobized surface, with a static contact angle of 135.7°± 1.2°. The washing studies with a standard soap solution of the cotton samples with or without crosslinker showed that the crosslinked PSMA30 offered a good coating durability to the cotton. This waterborne resin based on surfactant-free latices displayed promising properties for coating applications and seemed to be very suitable for the hydrophobization of polar surfaces. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Reactive dyeing systems for wool fibres based on hetero-bifunctional reactive dyes. Part 2: Investigation of dyeing properties during the dyeing cycle

The dyeing behaviour during the dyeing cycle of a Sumifix Supra dye and some other commercial reactive dyes under various dyebath pH conditions was investigated. Studies of the dyeing of wool serge fabric indicated that the diffusion properties of hetero-bifunctional Sumifix Supra dyes generally lie between those of b-sulphatoethylsulphone (Remazol dyes) and monochlorotriazine (Procion H dyes).     

Optimization of a Fabric Softener Formulation with an Electrochemical Sensor and Streaming Potential Measurements

An electrochemical, cationic, surfactant-selective sensor based on multiwalled carbon nanotubes (MWCNT) functionalized with a sulfate group and the cetylpyridinium ion (MWCNT–OSO₃⁻CP⁺) as a sensing material was used for optimization of the formulation of a fabric softener. Potentiometric titrations were performed and response measurements were obtained using four cationic surfactants (CS) of technical grade and four CS of analytical grade. The slope closest to Nernstian was obtained for di-(tallow carboxyethyl) hydroxyethyl methylammonium methosulfate (MAS) (59.5 ± 1.1 mV/decade of activity in water and 57.5 ± 1.3 mV/decade of activity in CaCl₂). When using CS as analytes in potentiometric titrations, the best accuracy (99.8%) was obtained when using MAS; therefore, it was chosen as the CS for the fabric softener formulation. Due to the better properties of fabric softeners with silicone in their formulations, four silicones at several concentration levels were used as potential additives. Based on the stability and viscosity of the system, the diquaternary polydimethylsiloxane (DPS) (w = 0.19%) was chosen for the fabric softener formulation. The pH did not significantly influence the potential when in the range of 3–8 or the recovery of potentiometric titrations when in the range of 3–7. The application profile of the CS was assessed through streaming potential measurements of reference fabrics in an electrokinetic analyzer. The obtained electrokinetic parameters indicated on lag in adsorption of model fabric softener (MFS) based on MAS (w = 9%), with the addition of silicone DPS (MFS 3), on cotton and polyester fabrics, but advantage in stability when compared with other MFS investigated.     

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.     

Reductive Cyclization of (3-) and (4-Oxoalkyl)-9,10-anthraquinones to the cyclopenta[a]anthraquinone and naphthacene-5,12-dione systems

Reductive cyclization of the 1-hydroxy-3-(3-oxoalkyl)-9,10-anthraquinones 2, 9 and 10 yields the angularly condensed cyclopenta[a]anthraquinones 3, 21 and 22a under neutral conditions (DMF/Na₂S₂O₄). By contrast, the linear cyclopenta[b]anthraquinone 23 is isolated from 10 applying the usual alkaline Marschalk conditions (aqueous methanol, NaOH, Na₂S₂O₄). The linearly condensed 5,12-naphthacenequinones 24–28 of different degree of saturation are obtained in good combined yield from the corresponding 1-hydroxy-3-(4-oxoalkyl)-9,10-anthraquinones 19 and 20 under the conditions of the Marschalk reaction.     

Nanofiltration and ozonation for decolorisation and salt recovery from reactive dyebath

Three commercially available high exhaust dyes were used to prepare dyebaths of different shades and subjected to nanofiltration and ozonation. Colour removal, chemical oxygen demand reduction, permeate flux, ozone consumption and total organic carbon removal were analysed to determine the efficiency of nanofiltration and ozonation. It was found that both nanofiltration and ozonation showed a high degree of (>90%) decolorising efficiency. High total organic carbon removal (80%) could be achieved by nanofiltration while ozonation could achieve only a maximum of 55% total organic carbon removal. The treated dyebath was reused for dyeing the fabric and the fabric quality was compared for the different shades. It was found that the quality of the dyed fabric was good for all shades dyed with nanofiltration permeate. The quality of the dyed fabric was affected for dark shades dyed with the ozone decolorised dyebath.     

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.     

The use of membranes for the recycling of water and chemicals from dyehouse effluents: an economic assessment

The practical and economic feasibility of using membrance technology to recycle/reuse dyes and their associated proces waters and auxiliary chemicals from dyebath effluent in and textile plants is assessed. Factors affecting the practicality of recycling dyes include: the type of process used to dye the fabric, classes of the dye used, the effluent volume, the frequency with which the dye is used and the auxiliary chemicals added to the dyebath during the dyeing process. These considerations also apply to the suitability of recycling the process water associated with the dye. Other factors to consider include the water quality required for recycling and the stage of the process to which this water can be reintroduced. To assess the economics of dyebath effluent reuse, water company treatment and supply charges, and dye and chemical costs must be considered. Data from five textile dyehouses are presented.