Vat Dyes Research Articles

Green extraction of natural indigoid from Baphicacanthus cusia (Nees) Bremek using hydrophilic and hydrophobic deep eutectic solvent technology

This study focused on the development of an alternative and more environmentally friendly extraction solvent, a deep eutectic system (DES), for extracting indigoid pigments, specifically indigo and indirubin, from Baphicacanthus cusia (BC). BC is recognized in the textile industry as a natural vat dye and in traditional Chinese medicine as "Qing-Dai". It is known for treating inflammatory diseases such as psoriasis. In this study, 46 DES systems were compared with conventional methods. The hydrophobic DES, a terpenoid and fatty acid system comprising thymol:decanoic acid (DES40), and the hydrophilic DES, a choline chloride-based system comprising choline chloride: p-toluenesulfonic acid (DES19), showed significant extraction improvements. DES40 and DES19 achieved approximately 26-fold higher indigo content compared to classical ethanol and outperformed the harsh organic solvent dichloromethane. The green extraction process was optimized using a Box–Behnken design, considering parameters such as temperature, time and co-solvent. DES19 maximized indigo and indirubin content to 270.91±14.38 and 5.70±0.11mg/g, respectively, while DES40 yielded 108.28 ± 3.9 and 0.16 ± 0.00mg/mg/g, respectively. Safety evaluations using a cell-based MTT model with human skin cells in keratinocytes and fibroblasts showed that both DES19 and DES40 were safe at all concentrations tested. These results indicate that a more environmentally friendly solvent technology for the extraction of indigoids from BC using the DES is an efficient and potential application in the textile and pharmaceutical industries.

Optimized single-bath dyeing of bio-based nylon 56/cotton blends with vat dyes: Mechanistic insights and process enhancements

Nylon 56/cotton (N/C) blended fabrics have excellent durability and can cater to various clothing needs. However, the quality and value of textile garments are significantly influenced by the dyeing process. Due to variations in the structure and characteristics of nylon 56 and cotton fibers in blended fabrics, achieving consistent coloration is challenging, resulting in noticeable color discrepancies. To tackle these issues, this study focused on dyeing nylon 56/cotton blended fabrics in a single bath using vat dyes. The three primary colors of the vat dyes were selected to be suitable for these fabrics. Subsequently, the study explored the impact of different factors on color consistency and optimized the dyeing process conditions using response surface methodology. The findings revealed that fabrics dyed using the optimized process exhibited vibrant colors, uniformity, and excellent colorfastness to soaping and rubbing, surpassing standard requirements. Furthermore, the study delved into the dyeing mechanism of nylon 56/cotton blended fabrics, analyzing the kinetic and thermodynamic properties of dye adsorption on fibers. This analysis aims to provide a theoretical foundation for developing a rational dyeing process and offer guidance for practical production.

A comparative study of iron-complex mediated cathodic vat dye reduction with dyebath regeneration by ultrafiltration, and the conventional dyeing process

The huge consumption of fresh water in the textile dyeing industry is a consequence of the use of chemicals, dyes and processes that are not compatible with recycling techniques. In this work pilot scale vat dyeing of yarn cones with use of electrochemically regenerable iron-complexes as reducing agents was investigated. A combination triethanolamine and heptagluconate was used for stable complexation of iron(III/II) at dyebath temperatures up to 80°C. At the end of the dyeing step the used dyebath was collected and oxidised by air oxygen. The dispersed oxidised vat dye was removed by filtration using a 0.45 µm PTFE membrane. A comprehensive analysis of the relevant waste water parameters demonstrated the potential of the technique to reduce the water consumption of the dyeing step by 68 % and to achieve significant reduction in chloride (-87 %), nitrate (-83 %) and sulphate (-99.6 %) load. Dependent on colour depth a replacement of single-use chemicals by this new technical concept will lead to significant chemical savings between 18 % and 72 % compared to the state of the art processes.

Early prediction of fabric quality using machine learning to reduce rework in manufacturing processes

The increasing competition and rapid technological advancements in today's business world have raised customer expectations. People now expect quick delivery, low prices, and high-quality products. As a result, companies must adapt to this competitive environment to survive. Rework, which is a significant cost in production, increases expenses, reduces production efficiency, and can lead to customer attrition. Research shows various efforts across different sectors to reduce rework, although there is still a gap in the textile sector's fabric dyeing units. Common problems in these units include non-retentive colors, customer dissatisfaction with shades, and repeated dyeing due to environmental factors or dye vat issues. This study uses logistic regression and artificial neural networks models from machine learning to predict which fabrics will need rework, using data from a textile company in Bursa. The analysis indicates that artificial neural networks models perform better.

Improved coloration of hemp fabrics via low-pressure argon plasma assisted surface modification

Interest in hemp as a viable cellulosic fibre for clothing has increased, driven partly by its economic benefits and the importance of natural renewable materials in emerging circular economies. However, the coloration and chemical finishing of lignocellulosic fibres such as hemp typically require large quantities of water and chemicals. Argon plasma pretreatment provides a way of modulating the physical properties of hemp fibres to improve the coloration process without compromising other bulk properties such as tensile strength. Such plasma treatments may contribute to alleviating the negative environmental impacts associated with liquid pretreatments, heating, or the use of auxiliary chemicals. Dyeing of hemp fibres is particularly challenging due to its crystalline chemical structure. In this study, low-pressure argon plasma-assisted surface modification of woven hemp fabrics up to 600 s at 40 and 80 Hz was explored for enhanced dyeability, resulting in enhanced dye-fibre bonding. Fourier-transform infrared spectroscopy and Raman spectroscopy of argon plasma pretreated hemp fabrics produced no noticeable changes in the functional groups of the fibres, but a physiochemical modification was observed in terms of the density of polar groups. Scanning electron microscopy (SEM) images revealed marked morphological changes including nano-etching of the fibre surface at certain argon plasma process conditions. The pretreatment process increased fibre hydrophilicity, and enhanced reactivity of the surficial –OH groups towards fibre-reactive and vat dyes, resulting in higher colour strength in dyed woven hemp fabrics. Overall, we envisage such plasma pretreatments may impact positively on the material and energy efficiency of the hemp fabric dyeing process.

Forensic discrimination of fiber microspectrophotometry data by resampling and repeating two-sample hypothesis testing

Textile fibers are important forensic trace evidence in criminal investigations. Colored textile fibers are often analyzed using non-destructive microspectrophotometry. However, when the spectra of questioned and known samples are very similar, it is difficult to compare the spectra visually. Chemometric methods, such as principal component analysis and agglomerative hierarchical clustering, have been applied to microspectrophotometry data. In this study, we used two-sample hypothesis testing as a chemometric approach for discrimination of fiber samples without reducing or eliminating the dimensionality of the data. Cotton fibers dyed with vat dyes were analyzed by microspectrophotometry. We examined suitable data types and statistical methods for test fiber samples by resampling and repeating hypothesis testing. A combination of spectral data type and statistical method was identified that provided a good balance of type I (false exclusion) and type II (false inclusion) error rates in two-sample hypothesis testing of the fibers.The main advantage of our chemometric approach is that an appropriate method for samples can be selected by using the type I and II error rates. Furthermore, our method can use all the measured data for the calculation without reducing or eliminating the dimensionality of the data, so it is not necessary to reduce variables or smooth the spectrum. This statistical method also requires no training set. Therefore, two-sample hypothesis testing could be applied to fibers of different types, colors, or materials from those used in this study. Resampling and repeating two-sample hypothesis testing technique is promising as a new chemometric approach for comparing microspectrophotometry spectra.

Spin-dyeing of cellulose fibres with vat dyes using the Ioncell process

Estimated 20 % of global clean water pollution is attributed to textile production. Dyeing and finishing processes use an extensive amount of water and chemicals, and most of the effluents and wastewater is released into the environment. In this study, we explore spin-dyeing of man-made cellulosic fibres (MMCFs) with vat dyes using the Ioncell process, circumventing the ubiquitous use of fresh water and potentially reducing effluents streams to a great extent. Spin-dyeing is an established process for synthetic polymers but is not common for MMCFs. Regenerated cellulose fibres were produced through dissolution of dissolving pulp in the ionic liquid 1,5-diazabicyclo[4.3.0]non-5-ene acetate. The produced fibres were processed into yarn and a jersey fabric was knitted. Mechanical and colour fastness properties were tested. The fibres properties were also assessed through SEM, birefringence, and crystallinity measurements. Fibres with excellent mechanical properties (tenacity higher than 50 cN/tex) and colour fastness were produced, with most samples receiving the highest or next highest performance grade. The spun-dyed fibres also hold great potential to be recycled themselves without colour change or loss in colour intensity. Textiles with colours produced in large quantities such as black or navy blue could be the first market entry point.

Vat Dye Molecule–Proton Dual Adsorption Catalysis Based on Molybdenum Disulfide for Sustainable Textile Dyeing

Vat Dye Molecule–Proton Dual Adsorption Catalysis Based on Molybdenum Disulfide for Sustainable Textile Dyeing

Indigo as a Low‐Cost Redox‐Active Sorbent for Electrochemically Mediated Carbon Capture

AbstractClimate change has driven the need for carbon capture to mitigate anthropogenic greenhouse gas emissions, yet current thermochemical methods are hampered by high energy intensities. Electrochemically mediated carbon capture (EMCC) utilizing redox‐active carbon dioxide (CO2) carriers is an attractive alternative for carbon capture. Here, an economical vat dye compound, indigo, is presented, which can reversibly capture and release CO2 upon electrochemical reduction and oxidation, respectively. Electrode and electrolyte engineering strategies are utilized to improve the reversibility and stability of indigo for EMCC. A bench‐scale prototypical fixed‐bed carbon capture device is constructed to demonstrate indigo's EMCC performance under various practically relevant conditions, such as simulated flue gas and extremely dilute sources pertinent to direct air capture. A hybrid sorbent electrode‐gas diffusion layer approach is revealed to alleviate CO2 mass transport limitations, achieving ≈80% CO2 capacity utilization under a 15% CO2 feed stream. Furthermore, a reactive‐diffusive mass transport model is developed to illustrate engineering approaches that can be universally applied to optimize fixed‐bed EMCC systems. This work advances the potential for a class of low‐cost sorbents for EMCC while underscoring the importance of molecular, electrolyte, materials, and device engineering strategies to enable high‐performance carbon capture.

Dyeing of Cotton and Wool Fibers with the Aqueous Extract of Alnus glutinosa: Evaluation of Their Ultraviolet Protection Factor, Their Color fastness and the Antioxidant Activity of the Aqueous Extract

The aim of the present study is to evaluate the dyeing properties and behavior of the aqueous extract of Alnus glutinosa leaves when applied on cotton and wool fibers. The antioxidant activity and the total phenolic content of the aqueous extract were calculated. The colorfastness of the dyed samples such as washing, acid and alkali perspiration, wet and dry fastness and light fastness was performed. The ultraviolet protection factor (UPF) which is a measurement of the protection offered by the dyed fabric substrates against ultraviolet radiation was also assessed. It was found that Alnus glutinosa aqueous extract shows exceptionally high antioxidant activity and high phenolic content. The dyed samples showed astonishingly high light fastness approaching the light fastness of synthetic dyes such as the vat dyes or metal complex dyes. The conferred protection of the dyed samples against the distractive ultraviolet radiation is exceptionally high as this is demonstrated by the high UPF measurements of the dyed samples.

Development of effective coloured flame-retardant finishing for cotton fabric

Coloured flame-retardant (FR) dyes are important for applying cotton textile materials. In this study, we have developed flame-retardant coloured cotton fabric (FR@Coloured cotton fabric) using FR-Vat dye. The flame retardant vat dye (FR-Vat dye) was synthesized by the phosphorus group functionalization on active nitrogen and oxygen sites of vat dye, which was further dyed on cotton fabric called FR@Coloured cotton fabric. The synthesized FR@Coloured cotton fabric showed excellent flame retardancy and sustained for 315 s on continuous flame exposure. In contrast, only dyed cotton fabric entirely burned within 18 s. We observed excellent limiting oxygen index (LOI), i.e., 35 % and vertical flammability (char length) value, i.e., 3 cm, for synthesized FR@Coloured cotton fabric. This excellent flame-retardant property provides it an ideal material for practical application and opens a new window for synthesizing coloured flame-retardant fabrics with other dyes and broadens the flame-retardant area for different applications.

Effect of occupational exposure to vat-textile dyes on follicular and luteal hormones in female dye workers in Abeokuta, Nigeria.

Some synthetic dyes used mainly in textile industries have been associated with endocrine disruption, resulting in infertility, among other disorders. It is unknown if occupational exposure to Vat textile dyes among premenopausal dyers alters hormonal levels. We aimed at determining the probable effects of occupational exposure to Vat dyes on reproductive hormones of female textile dyers in the follicular and luteal phases while relating this to age categories and duration of exposure. Thirty-three premenopausal Vat textile dyers at "Itoku", Abeokuta, Nigeria, among a population of about 80 female dyers were age and sex-matched with 55 non-exposed (control) female participants. Using semi-structured questionnaires, socio-demographic, occupational details and the LMP of participants were obtained. Serum samples were collected in follicular and luteal phases and assayed for female sex hormones using Enzyme Immunoassay. Mann-Whitney U and Z- statistic were used for comparison of the two groups. P-value < 0.05 was considered to be significant. In the follicular phase, the result showed a lower mean FSH ranking (in age category ≤20 years) and higher (p<0.05) Estradiol ranking (in age category 31-40 years) in the exposed than the unexposed. Mean ranks of Progesterone and Estradiol in the luteal phase (age category 31-40 years) were higher (p<0.05) in the exposed, while Estradiol (age category ≥41years) ranked lower (p<0.05). Prolactin demonstrated a significant inverse relationship with the duration of exposure. Occupational exposure to Vat dye among female dyers in Abeokuta is associated with some sex hormone disruption which appears to be age and duration of exposure-related.

Dyeability and mechanical properties of banana fiber reinforced polypropylene composite

AbstractBanana fibers being highly strong and biodegradable, have always been an interesting aspect of polymer science. The research examines the pretreatment process to enhance the dyeability of banana fibers with synthetic dyes, followed by the preparation of polypropylene (PP) composites with dyed fibers to explore their mechanical properties. Raw banana fibers were extracted from the pseudo stems of banana plants for pretreating with sodium hydroxide and hydrogen peroxide and further dyed in the exhaust method using direct, basic, reactive, and vat dyes. Despite a decrease in fiber strength, the scoured‐bleached fibers appeared whiter and lustrous compared to untreated fibers. Direct dye exhibited a higher color strength (K/S) value of 20.7 and better wash fastness on average of 4‐3 rating compared to basic dye. Later polypropylene sheets were prepared using a Hot Plate Molding Machine, and composite specimens were fabricated by sandwiching the fibers between PP sheets and hot pressing. Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed minor bond formations between the dyed fibers and polypropylene matrix in composites showing significant bonding at NH, CH, and OH regions. The composites containing dyed fibers showed slight improvements in tensile strength and modulus which is at best 2% than that of untreated fiber.Highlights Direct and basic dyes were determined as the most suitable synthetic dyes. FTIR analysis revealed minimal bond formation between the fiber and PP matrix. Composites having dyed banana fiber showed little better mechanical features.

Coordination complexes of reduced organic dye isoviolanthrone with transition metals and lanthanides [Mn(II), Dy(III), Gd(III), Nd(III)

The reduction of a vat dye isoviolanthrone to the dianion state in the presence of metal-containing compounds yields binuclear coordination complexes. Two manganese(II) acetylacetonate units coordinate to isoviolanthrone2− (L) in {(K+)cryptand}2{[MnII(acac)2]2⋅L}2– (1) with an average Mn–O bond length of 2.022(2) Å. Dysprosium(III)- or gadolinium(III)-2,2,6,6-tetramethyl-3,5-heptanedionate (TMHD) units form {(K+)cryptand}2{[MIII(TMHD)3]2⋅L}2− (M = DyIII for 2 and GdIII for 3) with the length of the M−O bonds of 2.193(3) and 2.254(4) Å, respectively. Tris(cyclopentadienyl)neodymium(III) forms {(Cs+)cryptand}2{[Cp3NdIII]2⋅L}2–⋅C6H4Cl2 (4) with the Nd–O bonds of 2.264(2) and 2.308(2) Å length. The formation of isoviolanthrone2− is supported by their optical spectra, disappearance of the bands of the CO vibrations in the IR-spectra as well as elongation of the CO bonds in 1–4. High-spin (S = 5/2) MnII atoms in 1 have exchange interaction of J = − 0.122 cm−1 at g = 1.98. Lanthanides have weaker coupling through isoviolanthrone2− in 2 and 3 with J = − 0.029 and D = − 0.004 cm−1 for DyIII and J = 0.0019 cm−1 for GdIII. Complex 4 with two Cp3NdIII species demonstrates the χMT value of 2.33 emu⋅K/mol at 300 K, and this value is lower than the theoretically calculated value of 3.39 emu⋅K/mol. The decrease of χMT is observed in the whole 300–1.9 K range providing negative Weiss temperatures of –32 K. That is explained by magnetic behavior of Cp3NdIII similar to pristine Cp3NdIII. Complexes comprising MnII, GdIII, and NdIII show electron paramagnetic resonance (EPR) signals. Zero-field splitting (ZFS) is observed from MnII and GdIII allowing the estimation of zero-field splitting parameter D as − 0.047 and E close to 0 cm−1 for 1 and − 0.033 and − 0.020 cm−1 for 3. Complex 4 with NdIII manifests an asymmetric two-component EPR signal without ZFS. Weak antiferromagnetic couplings are explained by diamagnetism of isoviolanthrone2− and rather long distances between the metal centers of 15.47–16.25 Å. This study shows that the dianions of organic dyes are promising bidentate ligands for preparation of coordination complexes with d- and f-block metal ions.

Dyes and their Importance: A Review

The global market for pigments and dyes is forecast to reach 9.9 million tons and $26.53 billion by the year 2017, driven by the growth in key end-use industries. Before synthetic dyes and pigments were discovered, limited number of natural colorant has been obtained from plants, animals and minerals. The classification of colorants has become mandatory due to huge increase in kind and number of colorants. For this reason, colorants are classified based on their structure, source, color, solubility and application methods. In this chapter, dyes will be investigated in two different groups as accordance with chemical structures and application methods. The basic classification groups were determined as azo, anthraquinone, indigo, phthalocyanine, sulfur, nitro and nitroso dyes by considering their chemical structures. According to application method, they were grouped as reactive, disperse, acid, basic, direct, and vat dyes. However, the classification of pigments as organic and inorganic pigments is also regarded as an appropriate way.

Cathodic reduction of 2-hydroxy-1,4-naphthoquinone (lawsone) to generate 1,2,4-trihydroxynaphthalene as regenerable reducing agent for dispersed indigo

A central chemical step in the application of vat dyes is their reduction into the alkali soluble leuco-form. In denim production the indigo dye is reduced by catalytic hydrogenation, by use of a chemical stock vat or by cathodic electron transfer in presence of soluble mediator systems. In this study the potential of 2-hydroxy-1,4-anthraquinone (lawsone) to serve as reversible redox couple for indirect cathodic reduction of dispersed indigo was investigated. Results from cyclic voltammetry, voltammetry in flow cells equipped with different cathode material and batch electrolysis experiments in presence of dispersed indigo demonstrate successful electron transfer from cathodically reduced lawsone to dispersed indigo above pH 12.5. At this pH the di-anion of 1,2,4-trihydroxynaphthaline is present in solution. At lower pH e.g. pH 11.5 the mono-anion is present, which is not able to reduce indigo molecules. For the study synthetic chemicals have been used as a model, however when the chemically equivalent natural colorants henna and indigo are used instead a new route for a fully bio-based indigo dyeing becomes available.

Structure of four vat dyes and of violanthrene

The structures of four industrially valuable vat dyes are solved for the first time: 1,1′-diethyl-[3,3′-bidibenzo[cd,g]indazole]-6,6′(1H,1′H)-dione (Vat Red 13, Cibanone Red 6B, Carbanthrene Red G 2B, Ahcovat Rubine R), 16,17-dimethoxyviolanthrone (Vat Green 1, Caledon Jade Green, Jade Green Base, Indanthren Brilliant Green B), pyranthrone (Vat Orange 9, Ahcovat Golden Orange G, Benzadone Gold Orange G, Pigment Orange 40), 2,8-diphenylanthra(2,1-d:6,5-d')bisthiazole-6,12-dione (Vat Yellow 2, Anthra Yellow, Tyrian Yellow A-GC) and violanthrene. Violanthrene was obtained by reduction of 16,17-dimethoxyviolanthrone with sodium metal in ethanol. The single crystals were grown by vacuum sublimation and examined with a synchrotron radiation source. The structures of all the four vat dyes represent a stacking motif, whereas violanthrene molecules form sandwiches of two molecules. The interplanar distance between the molecules in the stacks (sandwiches) is 3.35–3.48 Å which is typical of polycyclic aromatic compounds.

A novel environmental friendly and sustainable process for textile dyeing with sulphur dyes for cleaner production

This investigation herein primarily focuses on developing a new textile dyeing process with sulphur dye class at room temperature using bacterial Lysate. Sulphur dyes are applied on cotton to produce dark shades at a lower cost, primarily providing excellent colour fastness, except against chlorinating agents. The insoluble sulphur dyes, like vat dyes, are first reduced and then applied as soluble leuco compounds that need to be kept under alkaline conditions, along with a reducing agent. The conventionally followed method of dying process involves the process of reduction of dyes using hazardous chemicals as reducing agent and alkali at higher temperature as well as subsequent dyeing at higher temperatures (60–80 °C) varying with the nature of dyes and processes. It eventually eliminates traditional heating arrangements and achieving easier control of the dyeing process at room temperature than at high temperatures. This investigation compares the newly designed processing route with the followed traditional process in the context of exhaust dyeing and rope dyeing methods with padding mangle. In addition, it involves in substituting the conventional reducing agent i. e. sodium sulphide partially with sodium hydrosulphite for sulphur dyeing. In nut-shell, this process comprises of reduction of dyes in the presence of an alkali agent, a reducing agent and a catalytic agent, wherein the reducing catalytic agent is a bacterial Lysate, establishing it to be environmentally viable, energy and cost effective, and sustainable dying process along with promising improvement quality in terms of dye uptake and comparable fastness properties.

Solvent-based stripping method for dyed cellulosic textiles

The post-consumer textile waste may contain several dyes, and it is difficult to predict the type of dye present in it. The chemistry of dyes and their bonding with textiles are not similar; therefore, colour can be stripped off using a specific method pertaining to a specific dye-fibre combination. However, the common decolourisation method will be highly sought-after to solve such limitations. The present investigation deals with the combined stripping of cellulosic textile materials dyed with Direct, Reactive, Vat and Sulphur dyes, followed by optimisation. Sodium hydroxide and sodium hydrosulphite were used as stripping agents together with a solvent and water mixture during the process of stripping. The optimised recipe obtained was 20 g/l sodium hydroxide and 20 g/l sodium hydrosulphite at 90 °C for 20 min with a 50/50 water/DMSO (Dimethylsulphoxide) ratio. It has been found that solvent-based and conventional stripping perform equally well on direct and reactive dyed fabrics. However, conventional stripping cannot remove vat and sulphur dyes. Contrarily, the same colours showed greater than 90% stripping efficiency in solvent-based procedures.

Application of sonicated chitosan for the remediation of vat dye bath wash: optimization studies using Box–Behnken model

Application of sonicated chitosan for the remediation of vat dye bath wash: optimization studies using Box–Behnken model