Innovations in Waterless Dyeing Technologies for Textiles
It is no secret that the textile industry is one of the largest water consumers, requiring vast amounts of water for various processes in its production. However, Earth’s freshwater only accounts for 2.5%, with more than 97% being saltwater. Within that 2.5%, over 68% of the freshwater is locked up in ice and glaciers, with 30% of it in the ground. This means that rivers and lakes are the sources of most of the water people and industries use every day, including the textile industry. Meanwhile, rivers and lakes only constitute about 22,300 cubic miles (93,100 cubic kilometers), which is about 1/150th of 1% of the total water in the world.
Water is utilized extensively in all aspects of textile production, such as dyeing, both in terms of fresh water input and effluent discharge. Many pretreatments and finishing processes, such as washing, scouring, desizing, mercerizing, printing, and bleaching, require water as a solvent. For instance, take a single pair of jeans. The United Nations confirmed that to create such a garment from raw material to end product requires around 7,500 liters of water, which is the same amount of water the average person drinks over a period of 7 years. This fact, combined with mass production and the trend of fast fashion, is no wonder that the textile industry is one of the leading water-intensive industries globally. As the demand for textiles continues to grow, it is essential for the industry to adopt sustainable practices to mitigate the impact on Earth’s water resources.
Thankfully, in recent years, a number of methods have been developed to conserve and reduce water usage in and around textile mills worldwide. These water-efficient technologies have enabled the industry to decrease water consumption during production processes. Examples include membrane filtration, closed-loop systems, and advanced dyeing techniques, which we will discuss in detail in the sections below.
When it comes to water consumption in textile mills, the dyeing sector accounts for 15-20% of the overall wastewater flow. It can generate millions of gallons of dye wastewater on a daily basis. Notably, yarn dyeing uses around 60 liters of water per kilogram of yarn. To color just two pounds (one kg) of cotton fabric, anywhere from 25-40 gallons of water (over 100 liters) is required. Depending on the type of dye used, dyeing water usage ranges from 30-50 liters per kg of cloth. Due to the significant consumption levels of traditional dyeing methods, many companies have started to implement advanced dyeing techniques that do not require as much water, such as air dyeing and supercritical fluid dyeing, both of which are waterless dyeing technologies.
Unlike traditional dyeing machines that use a lot of water, air dyeing only uses a little bit of water in the process. In the case of air dyeing, the machine turns the dyeing fluid into tiny droplets and mixes it with air that’s moving very fast then spray this mixture over the fabrics to color them. Since the fabric moves through the machine on a flow of air and steam, it doesn’t need to be soaked in a lot of liquid like in traditional dyeing machines. According to an independent assessment, air dyeing uses up to 95 percent less water and up to 86% less energy, contributing 84% less to global warming, depending on the fabric and type of dyeing. Furthermore, some companies claim that air-dye technology allows them to print to order, reducing waste and extra output. Unfortunately, the air-dye technology is still relatively new and the cost of machine installation is high. As a result, we should support researchers who focus on developing low-cost, simple air dyeing procedures for natural and synthetic materials that use less water and emit almost no pollutants. This could be the future of textile dyeing technology
One company that is based in the Netherlands, DyeCoo, has developed the first commercially available textile dyeing machine that eliminates the need for water and processing chemicals in the dyeing process. The DyeCoo uses pressure and heating carbon dioxide to above 31.1 degrees Celsius, the temperature at which it becomes “supercritical,” a phase between a liquid and a gas. This allows dyes more easily to dissolve and to penetrate deeply into fibers without the use of water or bonding chemicals. The CO2 is then cleaned and 95 percent is recycled back into the machine to be reused.
Other advanced dyeing technology is the usage of membrane filtration. In the case of continuous dyeing, lower water consumption leads to a more concentrated waste stream, which requires a smaller membrane area for dye removal. As a result, a smaller membrane area is needed for removing dye from the waste stream, making the process more efficient and environmentally friendly.
Additionally, water consumption for exhaust dyeing of cellulose with direct dyes is also lower than for reactive dyes, making recycling possibilities more feasible. This is because exhaust dyeing processes generally use less salt, do not require fixation alkali, and achieve the desired level of wet fastness through special after treatments. These factors contribute to a more sustainable dyeing process that is easier to manage and has less environmental impact.
All in all, as the textile industry embraces these cutting-edge solutions, it moves closer to a more sustainable future that preserves Earth’s invaluable water resources while still satisfying the ever-increasing demand for textiles. The collective efforts of governments, businesses, and consumers in endorsing and adopting these sustainable technologies and breakthroughs are vital to securing a greener, more eco-conscious textile industry for future generations.