Textile industry is one of the largest consumers of water, energy, and chemicals. Traditional dyeing methods often release toxic effluents into the environment, causing water pollution, high energy use, and health risks. To overcome these problems, the industry is shifting toward sustainable dyeing techniques. Now sustainable dyeing techniques are becoming increasingly popular in the textile industry as it works to reduce its environmental impact.
In this article I will explain why sustainable dyeing is important and various popular sustainable dyeing techniques.
Why Sustainable Dyeing is Important?
Sustainable dyeing techniques aim to minimize water usage, reduce chemical waste, and save energy, making the textile industry greener and safer. Main reasons for sustainable dyeing are point out below.
- Environmental Protection: Reduces water pollution and chemical waste.
- Resource Efficiency: Saves water, energy, and raw materials.
- Cost Reduction: Lower consumption of chemicals and utilities in the long run.
- Health and Safety: Less harmful chemicals protect workers and consumers.
- Meeting Regulations: Complies with international environmental standards and buyer requirements.
Popular Sustainable Dyeing Techniques in the Textile Industry
1. Supercritical Carbon Dioxide Dyeing:
Supercritical Carbon Dioxide (CO₂) dyeing is a modern waterless dyeing technique developed to reduce water usage and pollution in the textile industry. Instead of water, it uses supercritical carbon dioxide (CO2) as the solvent. So, no wastewater is produced in this waterless dyeing method. CO₂ can be recycled within the system. Besides, it produces vibrant colors with shorter dyeing time.
The super critical fluids have low viscosity and high solubilizing power. This makes them suitable for use as a dyeing medium. They can dissolve dyes and penetrate the remote regions inside the fiber structure without any agitation. Among other super critical fluids, CO2 is considered for dyeing applications due to its nontoxic and noninflammable properties.
The dyeing in scCO2 is characterized by low mass transfer resistance and a high rate of dissolution of dyes. This helps in the penetration of the dye into the deep core of the fiber structure. Moreover, this is a waterless process eliminating the energy- intensive drying process. There are also negligible chances of the dye getting hydro-lyzed, and hence, most of the dye is available for reaction with the fiber. The scCO2 used in the process can be recovered. These are some of the advantages of using scCO2 as a dyeing medium over aqueous dyeing.
Super critical carbon dioxide has been used to dye natural as well as man-made fibers. Cotton has been dyed using disperse reactive dyes in scCO2 medium. It has been found that the increase in dyeing temperature helps in dye-fiber interaction in the scCO2 medium. Increased dyeing time helps in deeper penetration of the dye into the fiber. The process is completely water-free, and approximately 95% of the CO₂ used is recycled within the system, making it highly efficient.
2. Plasma-Assisted Dyeing:
With the aim of sustainable, innovative and eco-friendly dyeing technologies, plasma-assisted dyeing is gaining attention in the textile industry to improve dyeing efficiency and reduce environmental impact. One promising innovation is plasma-assisted dyeing, which modifies the fiber surface using plasma technology before or during dyeing. Plasma treatment improves dye absorption and reduces the need for harmful chemicals, making dyeing more eco-friendly and efficient.
Plasma is referred to as the fourth state of matter. The active ionic species of plasma have the capacity to break chemical bonds that result in surface modification of textiles. Hence, plasma is a dry technology that is utilized in dyeing as well as finishing treatments. Based on the gas used and the process conditions, plasma can be used to get different effects like cleaning, etching, and other surface functionalization properties. Plasma can be of two types according to the working pressure of the system: hot plasma and cold plasma. Owing to the degradation of textiles at elevated temperatures, cold plasma is used for the plasma treatment of textiles.
Wool shows a hydrophobic character due to the lipid content in its outermost epi-cuticle layer. This provides a hindrance to the penetration of water and chemicals during the dyeing process. Hence, surface modification is done by plasma treatment to increase the wettability and absorbency of the fiber. Dielectric barrier discharge plasma was used for this purpose. The reactive dye exhaustion on the fiber increased after the plasma treatment due to the introduction of nanoscale surface roughness that provided a pathway for the diffusion of the dye into the fiber interior. Cellulosic fibers like cotton have been treated with plasma and dyed with natural dyes that added functional properties to the dyed fabrics.
Polyester is the most popular fiber in the category of synthetic fibers. Due to its hydrophobic nature, it becomes difficult to dye polyester with natural dyes. It has also been treated with plasma through dielectric barrier discharge in air at atmospheric pressure. This treatment has introduced changes in the polyester surface that helped to reduce its hydrophobicity and hence increased its dyeability with natural dyes.
3. Air Dyeing:
Air dyeing is a revolutionary green technology in textiles. It is also a waterless dyeing technology where compressed air is used to transfer dye molecules into fibers. Water is used extensively in textile wet processing. To make wet processing sustainable, waterless technologies are being discovered. It colors textiles with negligible or no use of water. The air flow dyeing technology involves atomization of the dyeing liquor followed by mixing with high-pressure air flow. The fabric passes through a mixture of air streams that is emitted from the blower. The movement of fabric takes place with the help of air or a mixture of air and steam. This process provides bright, durable colors without wasting water. Air dyeing is widely used in sportswear, fashion wear, and upholstery where polyester and blends are common. Besides, it is suitable for industries aiming for eco-friendly and sustainable production.
The fabric absorbs the dye from the moisture saturated air flow, and hence, it is lighter than its weight in conventional dyeing. The light weight of the fabric helps to achieve high processing speed, without causing any damage to the substrate. The strain experienced by the fabric during processing is minimal and hence elastane fibers can be processed through this technology. Polyamide dyeing through air dye technology is also used for end-use applications like automotive, swimwear, etc. in other words, delicate fabrics can be dyed effectively with minimal use of water and energy. Moreover, the high processing speed of this technology helps to increase production with short-run cycles.
The high processing speed and minimal liquor ratio make this process sustainable. The reduction in chemicals also supports in overall cost reduction of the process. However, issues may crop up when dye solubility is a concern. Sometimes, the fabric tends to pack in on the lower end of the machine owing to the reduced liquor ratio. This may lead to the development of permanent wrinkles on the fabric. Hence the synthetic fibers should be heat set before they are dyed using this technology. The air dye technology opens up multiple designs of dyeing fabric. When two sides of the fabric are differently colored, it is called dye-to-dye contrast. When one side of the fabric is printed while the other face is solid colored, it is called dye-to-print. When both sides of the fabric are of the same color, it is called dye squared. When both faces of the fabric are printed differently, it is called print-to-print.
The air dye technology claims to reduce the use of resources like water and energy and hence is a sustainable approach. It is a cleaner way of producing dyed fabrics with rich shades. There are no limitations relating to the washing of the air dyed textiles. This technology is, therefore, being increasingly accepted as a sustainable alternative to the conventional dyeing of textiles.
4. Foam Dyeing:
Foam dyeing is a low-liquor dyeing method where dyes and chemicals are applied to fabric in the form of foam instead of a liquid solution. This technology is considered an energy-saving and eco-friendly alternative to traditional dyeing methods and is gaining adoption in textile manufacturing. In this process, a stable foam is created by mixing air with a small amount of water, dyes, and auxiliaries. The foam is then applied evenly to the fabric surface, and through heat treatment, the dyes are fixed onto the fibers. It is particularly useful for continuous processes like dyeing, printing, and finishing, and is widely applied in fabrics such as denim, cotton, and blended textiles.
5. Ultrasound-Assisted Dyeing:
Ultrasound-assisted dyeing is an advanced textile dyeing technique that uses high-frequency sound waves (ultrasound) to create microscopic bubbles in the dye bath. This cavitation enhances dye diffusion, improves fiber swelling, and breaks up dye aggregates. This technology improves how dyes penetrate fabric fibers, resulting in better color quality, faster dyeing, and a more environmentally friendly process. Ultrasound-assisted dyeing was first discovered in the mid-1900s. Ultrasound has a frequency range that is inaudible to humans. Ultrasound provides some distinguished advantages in dyeing compared to conventional dyeing techniques. It helps to accelerate the process of dyeing and gives good results in mild processing conditions. The effect of ultrasound on the solubility of dyes and dye uptake by textiles has been studied by various research groups. The primary reason for the improvement in the dyeing process is due to the cavitation phenomenon and its consequent effects.
Ultrasound-assisted dyeing is applied in cotton, wool, and silk dyeing, especially with natural dyes, to improve color uptake and fastness. It is also used for eco-friendly processing, reducing water and chemical use, and in developing functional textiles like antibacterial and UV-protective fabrics.
6. Use of Natural Mordants in Dyeing
Natural mordants play a vital role in sustainable textile dyeing by improving color fastness and shade diversity without harming the environment. They are especially important in natural dyeing processes for producing eco-friendly textiles.
Mordants are an important element of textile dyeing. Natural dyes generally do not possess an affinity toward the textile substrate. Mordants act as a bridge between the fiber and the dyes. They are substantive to dye as well as fiber. Hence, dyes with little or no affinity toward textile can easily be fixed on the substrate with the help of mordants. Depending on the time of mordant application in the sequence of dyeing, the dyeing process can be classified as premordanting, meta/simultaneous mordanting, and postmordanting. The treatment of textile with mordant prior to dyeing is called premordanting, while the treatment of textile with mordant after dyeing is called post mordanting. Simultaneous mordanting involves the dissolution of mordant as well as a dye in the dyebath during dyeing operation. In the view of sustainability in textile processing techniques, biomaterials are being increasingly researched for mordanting properties. Some of the naturally occurring compounds that are used as mordants are tannins and tannic acid. Myrobolans and sumach are natural substances that come under this category. The fruit of Terminalia chebula is called myrabalan. The tannin in myrabolan is ellagitannic acid which is contained in the peel of the fruit. It is used in dyeing cotton and black dyeing of silk. Sumach contains gallotannic acid which is not used in dyeing light shades due to the red coloring matter present in it.
7. Nanotechnology in Dyeing:
Nanotechnology has made a cutting-edge entry in the field of textile wet processing. In dyeing, nanotechnology helps achieve better color quality, stronger bonding, eco-friendly processes, and multifunctional textiles. Fibers having varied dimensions can be dyed using natural dyes. In one such study, natural dye extracted from roselle calyx was used to color nanofibers during bubble electrospinning. Polyvinyl alcohol (PVA) nanofibers were dyed using this naturally extracted dye. The dye could effectively penetrate and color the nanofibres.
Isotactic polypropylene (PP) is also a fiber that is difficult to dye because of its highly regular arrangement of monomer groups resulting in high crystallinity. Hence, nanotechnology has been utilized to dye the otherwise difficult to dye iso-tactic PP fiber. The nanocomposites of PP are dyeable as it is believed that the dye sites are formed at the places occupied by the nanoparticles. Nanoclays are generally used as nanoparticles. They are sometimes surface-modified to increase the dye affinity of the composite.
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The effect of nanoclay addition to a blend of polypropylene (PP) and polytri-methylene terephthalate (PTT) was studied in terms of its structural properties and dyeability with acid and disperse dyes. The fastness properties of the dyed samples were also investigated. On the other hand, the nanoclay acts as a nucleating effect and hence helps to improve the overall crystallinity of the fibers. The disperse dye-ability of the fibers is improved as observed from the enhanced K/S values. This is mainly due to the nanoclays acting as sorption sites because of its high surface area leading to van der Waals’ and ionic interactions with the dyes. The presence of quaternary ammonium salts in the nanoclays serves as points of interaction with the acid dyes due to which the acid dyeability of the fibers was improved.
Nanotechnology in dyeing is an innovative and eco-friendly approach that improves color quality, reduces resource consumption, and enables multifunctional fabrics. Although still costly and developing, it has great potential for the future of sustainable textile dyeing.
Conclusion
Sustainable dyeing techniques represent more than just an environmental necessity. They offer exciting opportunities for innovation, efficiency, and quality improvement in textile production. Sustainable dyeing is key to reducing the textile industry’s environmental impact. By adopting natural dyes, waterless dyeing, low-impact synthetic dyes, and advanced eco-friendly technologies, the industry can conserve resources and protect ecosystems.
References
[1] Yusuf, M., & Shahid, M. (2022). Emerging technologies for textile coloration. In CRC Press eBooks. https://doi.org/10.1201/9781003140467
[2] Muthu, S. S. (2018a). Sustainable innovations in textile chemical processes. In Textile science and clothing technology. https://doi.org/10.1007/978-981-10-8491-1
[3] Blackburn, R. (2015). Sustainable apparel: production, processing and recycling. In Woodhead Publishing eBooks. https://eprints.whiterose.ac.uk/115429/
[4] Muthu, S. S. (2018). Sustainable innovations in textile chemistry and dyes. In Textile science and clothing technology. https://doi.org/10.1007/978-981-10-8600-7
[5] Kiron, M. I. (2022, November 8). Sustainable dyeing process in textile industry. Textile Learner. https://textilelearner.net/sustainable-dyeing-methods/
