SustainabilitySustainable Dyeing

Waterless Carbon Dioxide Dyeing is a powerful solution for Sustainable Coloration

Carbon dioxide dyeing, sometimes called CO₂ dyeing, is a cutting-edge and sustainable method of dying textiles. Traditional textile dyeing methods frequently use enormous amounts of water, chemicals, and energy, which has a negative impact on the environment and pollutes the water supply.

Supercritical carbon dioxide, which has the characteristics of both a gas and a liquid, is used in CO₂ dyeing. CO₂ may effectively dissolve and transfer dyes into textile fibers in this form, acting as a solvent. Pure powder chromophores are the main dyeing component in CO2 dyeing. CO2 dyeing ensures that garments are efficiently and effectively colored by employing powdered colors. This method can precisely control the dyeing procedure, resulting in brilliant and durable colors on the dyed textiles.

In the procedure, the fabric is loaded, the system is pressurized to achieve a supercritical CO₂ state, the cloth is colored, and finally, the system is depressurized to release the dyed fabric.

  • Loading: The fabric, required dyes, and auxiliary materials are loaded into a high-pressure dyeing tank.
  • Pressurization: The vessel is filled with carbon dioxide, which raises the pressure and temperature to reach the supercritical state.
  • Dyeing: The dyes dissolve and enter the textile fibers in the supercritical CO₂ state, producing the desired coloring.
  • Depressurization: When the pressure is reduced, the CO₂ turns back into a gas, leaving the colored fabric behind within the fibers.

CO₂ dyeing has proven effective for PET (polyethylene terephthalate) materials, providing efficient and thorough coloring with outstanding and long-lasting results. The dyeing medium of supercritical CO₂ ensures high dye penetration and homogeneous dispersion throughout the fabric structure. CO₂ dyeing dramatically reduces water consumption compared to traditional dying procedures, harmonizing with sustainability goals and lowering environmental impact.

While CO₂ dyeing has been chiefly used for PET fibers, attempts have been made to employ CO₂ with dispersion dyes to color other synthetic textiles such as nylon, polylactic acid (PLA) fibers, and PP fabrics. However, due to their nonpolar aliphatic structure and high crystallinity, these fibers provide problems. These synthetic fibers have a low dye sorption rate and poor fastness quality.

To improve fastness quality, dispersion dyes that interact with the polymer and establish covalent connections with functional groups must be carefully chosen. CO₂ dyeing, on the other hand, is less effective for natural textiles like cotton and wool.

Natural fibers are hydrophilic and contain polar groups, making using nonpolar supercritical CO₂ for coloring difficult. Natural fibers’ complex structure and composition make it challenging for CO2 to accomplish sufficient dye penetration and uniform color distribution. As a result, natural fiber CO₂ dyeing frequently results in poor color fastness.’

Figure: Material Scope in Supercritical CO₂ Dyeing

Advantages of CO₂ dyeing

The advantages of CO₂ dyeing over traditional dyeing techniques include their efficiency, sustainability, and circularity.The considerable decrease in water consumption is one noteworthy advantage. Contrary to conventional techniques, CO₂ dyeing does not require vast quantities of water for dye baths and rinsing.

The procedure reduces water consumption, saving valuable water resources and lessening the environmental effect of water use in textile dyeing by using supercritical CO₂ as the dying medium.

  • Using chemical auxiliaries and additives is reduced while using CO₂ dyeing, further increasing its eco-friendliness. This decrease in chemical use benefits both the environment and the safety and well-being of dyeing process workers while reducing the environmental effect.
  • CO₂ dyeing emphasizes energy efficiency as a crucial component. Compared to conventional dyeing methods, CO₂ dyeing uses less energy because it operates at lower temperatures. This contributes to a cleaner and more sustainable dyeing process by lowering carbon emissions and energy consumption.
  • CO₂ dyeing saves time. The procedure shortens the whole dyeing time, increasing productivity and using fewer resources because it does not require prolonged dye bath heating and rinse cycles.
  • CO₂ dyeing provides better dye penetration. Due to CO₂’s small molecule size and ability to penetrate textile materials, dye fixing and color fastness are improved. As a result, the dyed fabrics are guaranteed to keep their brilliant colors longer.
  • Dying without water equates to being entirely free from the availability of pure water wherever you are. In the middle of the Sahara, the fabric can be dyed. This creates new prospects for the textile sector by enabling closer production to the market, shorter lead times, and disconnection from water, the planet’s most precious resource.
Figure: Annual environmental savings for one CO₂ dyeing machine

Drawbacks and Limitations of CO₂ dyeing

CO₂ dyeing has many benefits, but it also has a few drawbacks and limitations. Dyeing natural fibers using supercritical fluids like CO₂ is a severe issue. Supercritical CO₂’s nonpolar nature limits its use in coloring polar hydrophilic materials. Supercritical CO₂’s low polarity makes it acceptable for coloring hydrophobic textiles. Natural fibers, which are hydrophilic and contain polar groups, have poor color fastness when dyed with sc CO₂.

This is owing to the restricted interactions of hydrophobic dispersion dyes with natural fibers. Adoption of CO₂ dyeing equipment and methods may be hampered by the high initial investment costs, especially by smaller textile companies. Difficulties may arise during the early stages of implementation due to the complexity of process control and the requirement for specialized knowledge. However, these obstacles can be overcome as technology develops and economies of scale are attained.

Dyecoo’s waterless dyeing technology at ITMA 2023

Dyecoo introduced its waterless dyeing technology at ITMA 2023. DyeCoo is the first manufacturer of industrial CO2 dyeing machines, offering a chemical- and water-free dying method for polyester fabric and yarn. LCA studies have verified this innovative approach, demonstrating considerable reductions in carbon and water footprints compared to standard methods.

Big brands and merchants have successfully adopted the most recent machine, DyeOx4, lowering their environmental impact significantly. DyeOx4, the fourth generation of CO2 dyeing equipment, has three independent dying vessels, allowing for a batch capacity of 120-180 kg for fabrics (depending on width, weight, and permeability) and up to 200 kg for yarn dyeing.

These machines are intended explicitly for polyester dyeing and can be used on knit, woven, and yarn fabrics. Notably, the entire dyeing process is water-free, which ensures environmental sustainability. The machines run without needing to process chemicals and have a phenomenal 95% CO2 recycling rate, making them energy-efficient and environmentally beneficial.

Figure: The DyeOx4 machine

Leading businesses and retailers are implementing CO₂ dyeing to fulfil sustainability goals, decrease environmental impact, meet consumer demand for sustainable products, stimulate innovation, and potentially save money. CO₂ dyeing allows brands to improve their environmental credentials by reducing water, chemical, and electricity consumption.

It satisfies rising consumer demand for eco-friendly fabrics and allows firms to stand out. CO₂ dyeing shows a commitment to sustainability and establishes brands as industry leaders. Furthermore, while the initial investment costs may be higher, the long-term benefits include operational improvements and possible cost reductions in water and energy prices.

Figure: A growing global adoption by leading brands & retailers

CO2 dyeing options provide a sustainable and environmentally friendly method for coloring textiles. CO2 dyeing helps to conserve resources, reduces pollution, and fosters a textile business that is more ecologically conscious by using less water, chemicals, and electricity. With ongoing advancements and increased adoption, CO2 dyeing has the potential to transform the dyeing process and shape a greener future for the textile industry.

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