pH control in the dyeing of polyamide with acid dyes

In this study, we report a number of pH control systems for the dyeing of polyamide fibres in a closed dyeing procedure. These include a phosphate buffer system and four pH sliding systems (ammonium sulphate and three hydrolysable organic esters). The dyeing properties of these systems are compared with their ability to control the pH. In comparison with sodium dihydrogen phosphate and ammonium sulphate, hydrolysable organic esters showed a much more effective pH sliding and, consequently, showed higher dyebath exhaustion and colour yields. They also showed very low conductivity, typically less than 0.5 mS. However, no difference in the levelness of the dyed samples among the five acid donors studied was observed and no difference in colour fastness of the dyed fabrics under various pH control systems was detected.     

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.     

Adsorption of a spent reactive dyebath by a chitosan bed: study of water reuse,bed regeneration,and UV/Fenton oxidation

In the present paper, a facile process combining chitosan bed adsorption and the UV/Fenton advanced oxidation process for treatment and reuse of spent reactive dyebath waste has been developed. The chitosan bed was very effective in decolouring spent reactive dyebath waste by adsorption enrichment of CI Reactive Red 195, and the water and sodium sulphate therein could easily permeate through the chitosan bed and then be recycled. Although the resulting recycled dyebaths were used 10 times as reconstituted dyebaths for dyeing with CI Reactive Red 195, the colour difference and the relative unlevelness index changes of the dyed samples still remained within acceptable levels. That was also true for CI Reactive Blue 19 in the 11th recycling cycle. As a result, an average saving of 60.4% and 93.4% for water and sodium sulphate, respectively, was achieved with the reuse process for the 11 dyebaths. The exhausted chitosan bed can be regenerated three times by dilute alkali without any significant sacrifice of adsorbability or mass. Emissions of the elution concentrates generated from three regeneration runs of the chitosan bed and then treated by UV/Fenton oxidation were found to meet the most stringent emission standards for both chemical oxygen demand and colour in China. Results reveal that the process combining chitosan bed adsorption and UV/Fenton advanced oxidation is promising for treatment and reuse of spent reactive dyebath waste, which can potentially benefit the environment and reduce operating costs.     

Decolorisation by Bacillus flexus of exhausted dyebaths containing CI Acid Red 249 and their reuse for wool dyeing

A dyebath containing left-over CI Acid Red 249 after dyeing of wool was completely decolorised using an isolated bacteria Bacillus flexus. Optimisation was carried out by varying the pH, temperature, dye concentration, and microbial loading. Complete decolorisation of a 50 mg l⁻¹ dye solution was achieved in 8 h at pH 7 and 37 °C with 10% v/v loading of the bacteria. The decolorised bath was utilised for dyeing of wool fabric with the same dye at 5% shade. This cycle of dyeing–decolorising–dyeing was repeated 5 times. The evaluation of dyed fabric was done using K/S, colour values, and fastness to light and washing. Comparison of a sample dyed with the conventional exhaust process showed that the dyeing quality is not affected for all five successive reuse cycles. The results are important from the viewpoint of reducing water consumption and chemicals.     

An innovative approach to the preparation of coloured and multifunctional silk material with the natural extracts from chestnut shell and black rice bran

In order to reutilise the byproducts of foods and crops to benefit the environment and economise on resources, the natural extracts from chestnut shell and black rice bran were applied in the simultaneous dyeing and multifunctionalisation of silk fabrics. In this work, the influence of pH value on dyeing properties was studied. The effects of the ratio of chestnut shell and black rice bran extracts and the application of mordants (aluminium potassium sulphate and ferrous sulphate) on the dyeing performance as well as anti-ultraviolet and antioxidant properties of treated silk were also discussed. The results showed that deep-coloured silk fabrics can be obtained when dyed with the two natural extracts as the pH value of the dyebath approached 3. The ratio of the two natural extracts and the use of the mordants have significant effects on colour depth, colour hue, colour fastness, and the functionalities of dyed silk fabrics. Combination dyeing and mordanting are able to enrich the colour hues of dyed fabrics. The washing, rubbing, and light fastness of the dyed fabrics after mordanting can be rated higher than grade 4. Moreover, the silk after combination dyeing has good UV protection performance (UPF > 30) and antioxidant activity. In addition, the functionalities of treated fabrics showed excellent washing fastness. This study reveals that chestnut shell and black rice bran extracts are suitable as natural colourants and multifunctional finishing agents for the preparation of coloured and multifunctional silk materials.     

Effect of temperature and bath composition on the dyeing of cotton with catalase-treated bleaching effluent

Conventional rinsing to remove residual hydrogen peroxide after the bleaching of cotton fabric can be replaced by enzymatic cleaning using catalases. Our previous study showed that dyeing in such catalase-treated bleaching baths results in a shade change on the dyed fabrics. The aim of this present study was to investigate the reasons for the unacceptable colour differences of the dyed fabrics. Experiments were performed to study the possible temperature-dependent dye interactions in the standard dyebath, and in the dyebath prepared with bleaching effluent. Fluorescence emission spectra were used to detect changes in the structure of the catalase related to the thermal unfolding and denaturing of the protein. It was found that the colour difference on the dyed textiles could be attributed to the temperature-dependent dye-enzyme interaction and precipitation, as well as to the complexity of the bleaching bath composition.     

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.     

Studies on indigo dyeing and diffusion by the film roll method

The influence of reducing agent, indigo concentration and dyebath pH on indigo dyeing and diffusion was studied for the film roll method. An almost linear relationship between the indigo concentrations in the dyed film and in the dyebath was maintained throughout the experiments. Two different calculation methods were used to obtain the diffusion coefficient and the surface indigo concentration in the film. Similar surface indigo concentrations were obtained from the two methods, but a lower diffusion coefficient was obtained by the approximate integral method. It was found that the dyebath pH is the dominant factor influencing the rate of diffusion of indigo and the colour yield of the dyed film. The dyebath pH also had a considerable influence on the reduction of indigo to leuco-indigo, a step that is essential to the dyeing process.     

The Effect of Buffer Systems on the Uptake of Acid Dyes by Wool and Nylon

For the measurement of adsorption of acid dyes by wool and nylon a dyebath pH of 4 can be achieved either by the use of aqueous solutions of acids, e.g. formic acetic or sulphuric acid or by the use of standard buffer solutions, e.g. acetic acid/sodium or ammonium acetate, phenylacetic acid/potassium phenylacetate or potassium hydrogen phthalate. In this work, wool yarn and nylon 6 filament have been dyed from aqueous solutions of C.I. Acid Reds 1 and 41 at a pH value of approximately 4.2 in the presence of either aqueous acetic acid or a selected pH 4 buffer. The effect of each buffer system on the rate of adsorption of each dye by wool and nylon fibres has thus been studied. It was found that, in some cases, the buffer system had a significant effect on the rate and extent of dye uptake. The use of potassium hydrogen phthalate, a primary pH standard, to produce a dyebath pH of 4.2 gave a greatly reduced adsorption of the two dyes by both fibres.     

Factors affecting the dyeability of cotton crosslinked with polycarboxylic acid

Improved dyeing properties of cotton crosslinked with polycarboxylic acids are produced by addition of reactive nitrogenous additives, such as alkanolamines and hydroxyalkyl quaternary ammonium salts, to the treatment formulation. Both N-methylolamides and polycarboxylic acids are effective for crosslinking cotton and bonding reactive nitrogenous additives to the cellulosic substrate, but dyeing characteristics of the finished fabrics are very different. In this study, the influence of the reactive additives and dyebath pH on the colour yields of cotton crosslinked with polycarboxylic acids and then dyed with anionic dyes were determined. Emphasis is on the dyeing properties of cotton finished with 1,2,3,4-butanetetracarboxylic acid or citric acid non-formaldehyde crosslinking agents, and alkanolamine hydrochloride or hydroxyalkyl quaternary ammonium salt additives.     

Simultaneous afterclearing and decolorisation by ozonation after disperse dyeing of polyester

A set of trials have been conducted to examine the efficiency of ozonation on afterclearing of disperse dyed poly(ethylene terephthalate) fibres. Ozonation was performed in the cooled dyebath after the completion of the dyeing cycle. The ozone concentration used was 12.8 ± 0.3 mg/min at a gas flow rate of 400 ml/min. The results indicate that 3 min ozonation time is appropriate to achieve wash fastness results comparable to conventional reduction clearing. These results were obtained with simultaneous dyebath decolorisation ratios up to 67% and without significant colour yield ( K/S value) losses of the dyed fabric. Ozonation periods exceeding 3 min caused significant colour yield ( K/S value) losses, although dyebath decolorisation ratios increased up to 82% and wash fastness properties further improved. The chemical oxygen demand of the dyeing process decreased up to 62% by the ozonation afterclearing. The advantages of the ozonation afterclearing process are savings in terms of water, energy and time and reduction in environmental load.     

Dyeing in catalase-treated bleaching baths

The conventional rinsing after bleaching to remove the residual hydrogen peroxide, harmful to the reactive colorants, was replaced by enzymatic cleaning using catalases. The catalase-treated bleaching liquor was reused for dyeing. Though no hydrogen peroxide was detected after the enzymatic process, the bleaching bath composition caused unacceptable colour changes on dyed fabrics. By varying the parameters of the dyeing process – dye, salt, alkali and enzyme concentrations – the colour difference could be reduced significantly and a good dyeing result could be achieved.     

Direct coloration of textiles with photochromic dyes. Part 3: dyeing of wool with photochromic acid dyes

Wool dyed with two isomeric water‐soluble spirooxazine‐based photochromic acid dyes, which were specifically designed and synthesised for direct application to protein and polyamide substrates, showed reversible change from a pale yellowish colour to blue when exposed to sunlight or UV light. With the first dye, significantly higher photochromic colour change was obtained when the wool was bleached, a feature attributed to a more open fibre structure which may facilitate penetration of the non‐planar dye anion and also the photocoloration reaction which requires a change in molecular geometry. Experimentation demonstrated that the optimum conditions for application of this dye to wool was from an aqueous dyebath at neutral pH and a temperature of 60 °C. An investigation using HPLC demonstrated that the dye was susceptible to decomposition in aqueous solution at higher temperatures and at lower pH values. The second dye was also applied to wool fabric to give a fabric with similar photochromic properties. The technical performance of the dyed fabrics, in terms of washfastness and photostability, was assessed.     

Colour variation in the dyeing of denim yarn with indigo

In this paper, various parameters of warp yarn dyeing using indigo dyes are investigated. These parameters include dye concentration, number of dips in the dyeing process, dyebath pH, amount of reducing agent, immersion time, oxidation (skying) temperature, effects of a wetting agent and soaping temperature. This study revealed that these parameters have varying degrees of influence on the resultant colour of the samples dyed. The degrees of variation in colour were expressed using the CIE L* a* b* system as well as the shade depth (Integ).     

Using ecological reducing agents instead of sodium sulphide in dyeing with CI Sulphur Black 1

Although low‐cost sodium sulphide is used as a reducing agent in most sulphur dyeing processes, it is considered to be environmentally unfavourable because of the resultant contaminated wastewater and the toxic hydrogen sulphide generated during the dyeing process. In the present paper, hydrazine sulphate, glucose, and sodium borohydride in the presence of sodium hydroxide were used as ecologically safe reduction systems for the CI Sulphur Black 1 dyeing of cotton fabric, and results were compared with those obtained using sodium sulphide. Dyeing processes were carried out at 90 °C for 60 min, and the colour yield (the K/S value), dyeing fastness, and breaking strength of dyed fabrics after soaping were measured. Response surface methodology was employed for experimental design and optimisation of results. Mathematical model equations were derived and statistical analysis carried out by computer simulation programming using Minitab v.15. At a dosage of 0.8 g l^?1 of CI Sulphur Black 1, the optimum sodium borohydride reduction system (sodium borohydride 0.47 g l^?1, sodium hydroxide 0.65 g l^?1) exhibited the highest colour yield and the lowest chemical oxygen demand of the residual dyebath.     

Extraction of natural dyes from Alpinia blepharocalyx K. Schum. for dyeing of silk fabric

Natural dyes were extracted from the leaves and stems of Alpinia blepharocalyx K. Schum. Analysis of the designed experiment revealed that extraction at a plant/water ratio of 1:20 could reach an optimal production of natural dyes when extraction was performed at 80 °C, for 4 h, under 20 min ultrasound, in the presence of 10 g/l sodium hydroxide, and with two extractions. The extracted natural dyes were applied to the dyeing of silk fabrics using different methods, including or excluding a mordant. It was found that mordants had a significant effect on the colour of dyed silk fabrics. The silk fabric dyed with the pre‐mordant method using potassium aluminium sulphate as a mordant showed a bright yellow with a higher colour strength. The optimal dyeing conditions were reached when the extracted natural dyes were pre‐mordanted with 10 g/l potassium aluminium sulphate at pH 6, and for a 20 min dyeing time.     

Pomegranate fallen leaves as a source of natural dye for mordant-free dyeing of wool

The application of metal mordants is usually necessary in dyeing of wool with natural dyes to improve the dye exhaustion and fastness properties. The majority of metal salts generally used as mordants are considered as toxic and it is important to find replacements for them. Plant sources with high content of tannins are good candidates as bio-mordant or colourant to overcome this drawback. In this study, the waste fallen leaves of pomegranate tree were used as a source of natural dye for the eco-friendly dyeing of wool fabric without the use of metal mordants. The dyeing process variables including dye concentration, dyebath pH, and temperature were optimised using response surface methodology to obtain the highest colour strength. The colour strength was increased by increasing the natural dye powder up to 100%owf while the optimum pH and dyebath temperature were 4 and 100°C, respectively. The sample dyed under the optimal condition exhibited good fastness properties against washing and light. This study approved the potential of Punica granatum fallen leaves for the dyeing of wool without any mordant, while high fastness properties were obtained.     

Improving the colour fastness of dyed nylon‐6 fabric by graft copolymerisation and curing of acrylic acid

The influence of grafting and grafting–curing of acrylic acid on the colour fastness of nylon‐6 fabric dyed with an acid dye of low wash fastness was investigated. The variables involved in grafting were initially optimised for pristine nylon‐6 fabric prior to grafting the same monomer onto the dyed fabrics. The highest graft yield achieved for the pristine and dyed nylon‐6 fabrics was 44 and 14% respectively. Grey scale testing and colorimetric analysis revealed that the highest colour fastness and the smallest drop in colour strength belonged to the dyed–grafted–cured nylon‐6 fabric. The colour components were measured, and the total colour difference of each sample after five washing cycles was computed. The specific colour difference showed that the implementation of either grafting or grafting–curing processes will alter the reference colour of the dyed fabric. The tensile strength of the grafted and grafted–cured fabrics was respectively 2.7 and 6.3% lower than that of dyed nylon‐6.     

The effect of dyeing on the hygral expansion of worsted fabrics. Part 2-the influence of metal cations

Wool gabardine fabric has been dyed in the presence of several different metal cations. Their influence on setting behaviour and subsequent dimensional properties is detailed. The use of extremely low levels of copper(II) sulphate as a novel dyebath antisetting treatment for wool is also demonstrated.     

Sonochemical destruction of textile dyestuff in wasted dyebaths

Ultrasonic degradation at 300 kHz of basic azo and reactive anthraquinone dyes was investigated in dyebath wastewater at acidic and near-acidic pH. For all conditions, it was found that colour decay was exponential, levelling off at a non-zero plateau and slowing down with increased acidity. It was also found that the bleaching rate of a dyebath was more sensitive to the dye structure than to the dyebath matrix. The rate of azo dye bleaching was slower than that of anthraquinone dyes at both test pH levels regardless of the unfavourable conditions in the latter dyebath against oxidation by hydroxyl radicals. The addition of hydrogen peroxide to the dyebaths rendered a slight enhancement in the degree of colour decay and a significant increase in the overall degradation of the dyestuff.