The Complexity of Dyes in the Textile Industry
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Our technical approach to dye compound-specific impact ????
When it comes to giving color to the fabric, one needs to optimize the dyeing process to satisfy various needs: The color needs to stay on the given type of fabric, the fabric needs to be evenly colored, and should not wash off easily.
This resistance to fading is called color fastness, which is due to the bonding forces between the applied dye and the textile fiber. Furthermore, the dye should not be costly yet to satisfy the set criteria.
While historically numerous natural dyes have been used to obtain desired visual effects, thanks to the growth of the chemical industry, now thousands of synthetic dyes and pigments are readily available to provide the exact shade and fastness we want. But what do we sacrifice??
The dyeing process consumes various resources: water, which subsequently needs to be treated to preserve water bodies; energy to heat the dyebath to the required temperature which can reach above 100°C; and other chemicals, known as auxiliaries, which facilitate the performance of the dyestuff on the fabric.
What are the problems associated with synthetic dyestuff?
Synthetic dyes are complex organic molecules, of fossil origin, which are produced through several chemical intermediates. Their structure varies based on the chromophore and the type of application.
However, since dye manufacturers are not legally required to share the exact composition or identify the chemicals in the product, it has been historically impossible for the fashion industry to fully study the upstream impact of chemical production.?
Going further, if the compound happens to be successfully identified, the next big issue is to obtain inventory data about the production processes as they are not widely documented due to confidentiality reasons.?
Furthermore, the main manufacturers of the dyestuff and their intermediates are in China and India, often with complex supply chains, not allowing for traceability.
How to classify dyes and their intermediates
However, despite the low amount of information available, it is still possible to reject the idea of using a generic proxy like “chemical, organic” to quantify their impact and create datasets following widely used frameworks.
The steps we followed are the following:
Through this approach, we have built compound-specific impact (where the raw material usage was fully documented) and highlighted production hotspots.?
Yet, to estimate the impacts of non-declared dye compounds, a technical classification is useful: As a means of averaging the modeled compounds in our database, a general cluster can be formed.?
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This way we can obtain proxy categories like “average reactive dye”, “average vat dye”, “average direct dye” etc, matching the ZDHC Roadmap to Zero Programme subcategories within the category of dyes and pigments.?
An example of Azo Dye
A comparative example shows for an azo dye, which contains anthraquinone as a building block, the effect of proxy choices in the four highlighted impact categories, for the sake of simplicity.?
Choosing the average organic chemical dataset from ecoinvent results in a massive underestimation of impacts, while choosing one of the building blocks only (anthraquinone) overestimates both climate change and the human toxicity impact categories.?
Why so? Because anthraquinone only makes up around 50% of the molar mass of the selected dye, the remaining 50% comes from organic syntheses completely different from anthraquinone.
Research Shift and Methodology
The estimation of the upstream impact of dyestuff is just one of the several problems associated with them.
Since synthetic dyes are designed to withstand light and water to maintain the original color of the garment, they are inherently hard to decompose when treating wastewater, and they often contain metals as a complexing agent which can further increase the toxicity of effluent wastewater.
These impacts are taken into account when analyzing the wastewater treatment facility of a dyehouse.
Due to this and the toxicity of decomposition products, we can see a shift in research towards natural pigments which are generally biodegradable by nature, and free of the fossil origins of synthetic dyes, but worth it only if they can perform the numerous advantages that synthetic dyes have set as standards.
The developed systematic impact estimation method is essential to facilitate a more sophisticated comparative analysis with potential natural dye alternatives.
Ready to calculate your dyeing impacts with our software and scientific approach? Book a demo of our solutions with our Sustainability Success Team!
This article was written by Enik? Kincses , Sustainability Analyst and Chemist at Sustainable Brand Platform. As a chemical engineer, she is working on filling the gaps by modeling the chemicals used in the fashion industry that increase the accuracy of our calculations. She shares the same mission as the rest of the team: "Making the fashion world more sustainable!" One chemical at a time ??