You Ask, We Answer Edition #4:  Waterless dyeing techniques

"You Ask, We Answer" – brought to you by Carbonfact's Head of Science. Each week Laurent Vandepaer answers one of your questions about sustainable materials, manufacturing impact, and energy transition in the apparel and footwear industry.

Before joining Carbonfact, Laurent led the integration of LCA into the sustainability and innovation efforts at On and performed LCA for other brands like Arc'teryx. Laurent also worked for several years in research with a PhD focusing on the deployment of LCA at a large scale.

Question: What are the environmental impacts of waterless dyeing techniques compared to traditional dyeing methods?

Asked by the Head of Sustainability from a lingerie brand

ANSWER

Waterless dyeing techniques, which do not use water as the main medium for coloring fabrics and garments, claim significant impact reductions (80-95% across various impact categories). The main non-aqueous dyeing techniques are supercritical CO2 dyeing, solvent-based dyeing as well as solution dyeing (we will cover the recent one in our upcoming series!).

Traditional Dyeing: Environmental Concerns

Traditional dyeing methods have a high environmental impact. These processes often involve large amounts of water, energy, and chemicals, leading to several significant issues:

• Water Consumption: Conventional dyeing requires vast amounts of water. For example, it can take up to 200 liters of water to dye just 1 kilogram of fabric.
• Water Pollution: The dyeing process generates wastewater contaminated with dyes, salts, and other chemicals, which can pollute rivers and groundwater if not treated properly.
• Energy Use: Heating water for dyeing consumes substantial energy, contributing to higher carbon emissions.
• Chemical Usage: Many traditional dyes contain harmful chemicals that can be toxic to aquatic life and harmful to human health if not handled correctly.

Waterless Dyeing

Supercritical CO2 Dyeing

This method uses supercritical CO2 instead of water to dye fabrics. Supercritical CO2 is a state of carbon dioxide where it acts both as a liquid and a gas, allowing it to penetrate fibers effectively. Key benefits include:

• 40% reduction in CO2 equivalent emissions
• 60% reduction in water use

While the actual dyeing process does not use water, water might still be used in the pre-treatment and post-treatment stages. The main environmental impacts are related to energy use. 

However, the reductions are notable, and as technology progresses and energy sources become more sustainable, these impacts may decrease further. Companies like DyeCoo and CleanDye are at the forefront of providing this technology.

Solvent-Based Dyeing

This technology uses organic solvents instead of water. The solvents are recycled in a closed loop, potentially reducing the energy needed to heat large water baths, which can offer environmental benefits. 

We received an environmental assessment from the brand's supplier that claimed even larger emissions than CO2-based dyeing. However, the reported reductions might be overestimated due to several factors:

• Life Cycle Emissions: The full life cycle emissions of the chemical and energy inputs used in the process may not be fully accounted for. Solvent inputs are crucial, and underestimating their impact could skew results.
• Pre- and Post-Treatment: As with supercritical CO2 dyeing, additional pre- and post-treatment processes may be required, which should be included in the overall environmental assessment.
• System Boundaries: It's essential to clarify the system boundaries of their studies. For example, does the assessment start with greige fabric entering the facility and end with finished fabric ready for assembly?
• Reference Technology: The reference technology chosen for comparison can significantly influence the perceived benefits. For instance, comparing against a batch dyeing process (which has a higher CO2 impact per kg of fabric) may show more favorable results for the new technology.

The environmental benefits are possible but more data should be collected. At this time we rejected the report supplied by the brand.

Real-World Example: H&M Testing CO2-Driven Dyeing Solution

H&M Group is exploring an innovative technology to replace traditional chemical-driven dye processes. The brand is set to test Deven Supercriticals’ Suprauno technology, which utilizes supercritical CO2—carbon dioxide in a fluid state—rather than water and chemical compounds for dyeing fabrics. The trials will be conducted in collaboration with their long-term manufacturing partner, India’s Arvind Ltd.

According to the partners, previous prototyping using Suprauno has yielded promising results when it comes to energy, water, and chemical use reduction. Deven Supercriticals’ testing on poly-cotton blended fabrics showed:

• 76% water savings
• 67% energy savings
• 90% fewer chemicals used

Waterless dyeing techniques offer promising reductions in environmental impacts, but it is crucial to consider the full life cycle and system boundaries when evaluating these technologies. 

About Carbonfact

Carbonfact is Sustainability software, built specifically for apparel and footwear brands as well as manufacturers to measure the environmental impact of their products and take actionable steps to reduce their footprint. Our Product Impact Simulation tool enables you to run what-if scenarios on a product level, where you can experiment with different material preparation techniques, suppliers, renewable electricity share, or transportation methods, and build concrete company-level decarbonization scenarios.

Do you have questions about sustainable practices, manufacturing impacts, or energy transitions in the apparel and footwear industry? We'd love to hear from you! Comment, send us a DM on Linkedin or email: youaskweanswer@carbonfact.com