Afterclearing by ozonation: a novel approach for disperse dyeing of polyester

A set of trials has been conducted to examine the efficiency of ozonation afterclearing on poly(ethylene terephthalate) fibres dyed with disperse dyes. The afterclearing process was performed in neutral distilled water at room temperature with 12.8 ± 0.3 mg/min ozone at 400 ml/min ozone gas flow rate. The results indicate that 1 min ozonation time is adequate to achieve wash fastness results comparable with conventional reduction clearing without significant colour yield losses. Ozonation periods greater than 1 min not only caused significant colour yield losses, but also caused a severe decrease of the breaking load of the fabric. The advantages of ozonation afterclearing are: savings in energy and time, as it is performed at room temperature for only 1 min, and decrease of environmental load as it avoids the use of the harsh chemicals used in conventional reduction clearing.     

Ozone applications for after‐clearing of disperse‐dyed poly(lactic acid) fibres

In this study, the effectiveness of the ozonation process, in neutral distilled water at room temperature, as a clearing process for disperse‐dyed poly(lactic acid) fibre fabrics is investigated. The efficiency of simultaneous decolorisation of dyebath effluent and clearing of dyed poly(lactic acid) in the cooled dyebath after completion of the poly(lactic acid) dyeing cycle is also explored. Conventional alkaline reduction clearing with sodium dithionite was chosen as a control clearing process for comparison. Wash fastness, colour difference, colour removal (in Hazen) and chemical oxygen demand values were determined and compared. Long ozone treatment times at high ozone dose resulted in unacceptable colour differences. The colour difference problem was solved by use of lower ozone dose; however, a warm soaping step had to be added to the after‐clearing sequence in order to achieve the desired fastness properties. A 33% reduction on the chemical oxygen demand load of the total process (dyeing + after‐clearing) could be achieved by ozone after‐clearing instead of using a conventional reduction clearing treatment. The addition of the warm soaping step to improve the fastness properties of the ozonated samples increased the total chemical oxygen demand of the process (dyeing + ozonation in water + warm soaping), but a 12–18% reduction on the chemical oxygen demand load of the total process was observed when compared with the conventional treatment sequence (dyeing + reduction clearing).     

Comparison of different ultrasound support methods during colour and chemical oxygen demand removal of disperse and reactive dyebath solutions by ozonation

In this study, the effects of ozonation, ozonation with ultrasonic bath and ozonation with ultrasonic homogeniser processes on colour and chemical oxygen demand removal properties of disperse (CI Disperse Red 60, CI Disperse Blue 337) and reactive (CI Reactive Blue 171 and CI Reactive Blue 19) dyebath solutions with and without dyeing auxiliaries were investigated. Chemical oxygen demand (in mg/l) and colour (in Hazen) measurements of the studied dyebath solutions were determined. The ozonation process caused simultaneous chemical oxygen demand removal during decolorisation. However, the improvement in chemical oxygen demand reduction was less than of that on decolorisation. The application of the combination of ozonation with ultrasonic homogeniser is the most efficient process and creates a great time advantage over the other process types studied (ozonation alone and ozonation with ultrasonic bath) to reach the same colour and levels of chemical oxygen demand removal.     

Afterclearing of disperse dyed polyester with gaseous ozone

The efficiency of ozone treatment for the clearing of disperse dyed polyethylene terephthalate fibres has been examined. The ozone treatment for the clearing of the dyed samples was performed by blowing the ozone gas from the ozone generator on to the wet fabric samples. The results indicated that 3‐ and 5‐min ozonation times were appropriate to achieve comparable wash fastness results with conventional reduction clearing without significant colour differences (ΔE* value) for the samples dyed with CI Disperse Yellow 23 and CI Disperse Blue 79, respectively; however, the ozonation time had to be increased to 15 min for CI Disperse Red 82. Tensile strength tests and scanning electron microscopy analysis indicated that the ozone treatment did not cause any severe damage to the fabrics. Ozone treatment for the afterclearing of disperse dyed polyester fabric can lead to energy and time savings and environmental load reduction when compared with conventional reduction clearing. This study tested a new method of ozone application for clearing of disperse dyed polyester by blowing ozone directly on to the fabric samples. This new method of application has the advantage of being readily adoptable for continuous treatment lines and lower water consumption.     

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.     

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.     

Investigation of a homogeneous activating ozonation method in the rinsing procedure of cotton fabric dyed with reactive dye

The textile dyeing process requires the consumption of large quantities of water, which includes huge amounts of coloured wastewater. Usually the rinsing of dyed fabric and the treating of the dyeing house wastewater are separated. The two independent processes not only increase the difficulty of wastewater treatment but also increase the costs of the treatment. In this paper, the ozone/tetraacetylethylenediamine active oxidation technology was employed to rinse dyed fabric and to decolorise the rinsing wastewater simultaneously. The effects of the rinsing conditions on the decolorisation ratio and the chemical oxygen demand Cr value of treated wastewater, and the K/S value, colour difference, tensile strength and fastness of dyed samples were investigated. The results indicated that the decolorisation ratio of the rinsing effluent was greater than 80% and the chemical oxygen demand Cr value decreased more than 58% by the ozone/tetraacetylethylenediamine rinsing process compared with that of traditional rinsing processes. Furthermore, the curve of decolorisation kinetics was in good agreement with a pseudo‐first‐order kinetic model. In addition, the decolorisation mechanism was also discussed after ultraviolet–visible and ultra performance liquid chromatograph–mass spectrometry analyses of the degraded dye molecule.     

The effect of liposome on dyeing mohair/wool blends

The aim of this study was to examine the use of liposome in the dyeing of wool and mohair fibres with acid dyestuffs. Soybean lecithin and cholesterol were used to form the liposome membrane utilised in the dyebath. Liposome production was performed according to the thin lipid layer method (Bangham Method) using a rotary evaporator. Two different forms of liposome were used for dyeing wool and mohair fibres. In its first form, liposome was utilised as an auxiliary agent, where it was added to a conventional dyebath at the beginning of the process. In its second form, dyes were encapsulated with liposome and then used in dyeing. The effects of these two different forms of liposome were compared with conventional dyeing. Dyeing was carried out at depths of shade of 0.5%, 1.0% and 2.0% using three different concentrations of liposome (0.33%, 0.66% and 1.33%). An analysis of K/S values, fastness to washing, and the alkali solubility of fibres was conducted. The fibre samples dyed in the presence of liposome exhibited very good fastness to light (grade 8). The wash fastness test results of the liposomal‐dyed samples were significantly better (grade 4‐5) than for those samples which were conventionally dyed. In the presence of liposome, the tensile strength of fibres was 20 gf, whereas it was 11 gf without liposomes.     

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.     

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.     

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.     

Reactive dyeing of silk using commercial acid dyes based on a three‐component Mannich‐type reaction

Acid dyes are employed for commercially dyeing silk, which results in ionic bonds between the silk fibroin and the dye. This generally leads to low wet fastness properties for dyed silk fabrics. In this work, three commercial acid dyes with aromatic primary amine structures were selected to dye silk using a Mannich‐type reaction, resulting in improved wet fastness of dyed silk by forming covalent bonds between silk fibroin and dye. The Mannich‐type reactive dyeing was applied to silk fabrics at both 30 and 90°C in trials. Dyeing at 90°C can shorten the dyeing time compared with dyeing at 30°C, even although dye exhaustion and relative fixation at 90°C were a little lower. The dyeing process was optimised when the dyeing temperature was 90°C, dyebath pH 4, dye‐to‐formaldehyde ratio 1:30 and holding dyeing time 60 minutes. The results showed that the dye exhaustion on silk fabrics for the three aromatic primary amine‐containing acid dyes exceeded 94% and their relative fixation was over 80%. Their washing and rubbing fastness reached grade 4 or higher. Hence, the colour fastness properties of dyed silk fabrics using the Mannich‐type reactive dyeing method is superior to the conventional acid dyeing method using the same aromatic primary amine‐containing acid dyes. The Mannich‐type reactive dyeing for silk fabrics at 90°C can be developed into a novel and rapid reactive dyeing method, promising an effective dyeing process with excellent colour fastness.     

Low chrome dyeing. Part 1 — the role of sulphamic acid in the afterchrome dyeing of wool

The role of sulphamic acid in the afterchrome dyeing of wool has been investigated. It was found that chromium residues in the dyebath effluent were significantly reduced when the commonly used formic acid was either partly or wholly replaced with sulphamic acid. The wash fastness properties of the wool fabric dyed in the presence of sulphamic acid were the same as those of wool fabric dyed by the conventional afterchrome process. There was no significant difference in the wool damage caused during the sulphamic acid-assisted dyeing process and the conventional formic acid dyeing process.     

pH control for dyeing polyamide in a reused acid dyebath

The pH control that can be achieved in a reused dyebath was investigated. The study involved a phosphate buffer system and four pH sliding systems, including ammonium sulphate and three hydrolysable organic esters. Instead of discharging the dyebath after each dyeing cycle, the residual dyebath was analysed using a UV-Vis spectrophotometer and reconstituted to the required concentration of dyes, auxiliaries and acid donors. The dyebath was reused for 10 cycles and colour reproducibility, levelness and fastness of the dyed samples were measured after each recycling. In comparison with ammonium sulphate and sodium dihydrogen phosphate, hydrolysable organic esters gave a stable and effective pH shifting in the dyebath reuse system. In addition, hydrolysable organic esters resulted in a very low amount of salt in residual dyebath. No deterioration in colour fastness of the dyed fabrics over 10 cycles of dyebath reuse was evident.     

Dyeing of cotton and jute with tea as a natural dye

Cotton and jute fabrics were dyed with an aqueous extract of tea, containing tannins as the main colorant species. The dyeing was carried out with and without metal salts as mordants, using three different dyeing methods: pre-mordanting, meta-mordanting and post-mordanting. The resulting wash and light fastnesses of the dyed fabrics were good to excellent. The colour of the fabrics was investigated on computer colour matching system in terms of K/S , and CIELAB colour-difference values. Deep shades ( K/S = 3.9) were obtained for jute in acidic media, while cotton fabrics could be dyed in medium depths ( K/S = 2.0) under identical conditions of dyeing.     

Reuse of ash-tree (Fraxinus excelsior L.) bark as natural dyes for textile dyeing: process conditions and process stability

The aqueous extract of ash-tree bark ( Fraxinus excelsior L.) was chosen as a model to study the shade reproducibility of dyeing on wool. A meta-mordanting process using FeSO₄·7H₂O mordant was chosen as a system with particular potential for industrial application. The exhaust dyeing process with immediate use of the extracts as a dyebath and direct addition of FeSO₄·7H₂O stock solution as a meta-mordant process showed good shade reproducibility and satisfying levelness of the dyed material. An increase of Fe( ii )-mordant above a dyebath concentration of 2–3 g l⁻¹ did not result in further colour depth. Extraction of 1–2 g of bark was found sufficient to dye 1 g wool yarn to the darkest colour possible; use of higher amounts of bark did not yield substantially higher colour depth. The quality of bark and the extraction step were found to be of significant importance for the colour depth; thus, in an optimised process, conditions of extract formation have to be well controlled.     

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.     

Enzymes as auxiliary agents in wool dyeing

The action of three enzymes has been comparatively studied when used as auxiliary agents in dyebath. The absorption rate of the dye, the colour differences between wool dyed with and without enzymes and the colour fastness were determined. The action of enzymes consists of increasing dye absorption and also seems to produce a better diffusion of the dye into the fibre. The use of the enzymes in wool dyeing offers the possibility of dyeing under mild temperature conditions.     

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.     

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.