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Monday Mailbag: What About Chemicals?

Another week, another ‘Monday Mailbag’! You know the drill – questions and answers have been edited for length and enhanced with as many links, photos, and video clips as we can muster.

Have a question of your own?
Our team can be reached at: connect@threadinternational.com


I run a website and blog called The Concerned Craft (Editor’s note: we love a good plug – check out their blog) which focuses on raising ecological and ethical awareness around fiber crafts (think home sewists, quilters, weavers, knitters, etc.).

I am curious about the process after the plastic is turned into flake and before it emerges as finished fabric.

Specifically, which chemicals are used in the processing and what impact the process may have in terms of chemical exposure and runoff, etc.?

Thanks for reaching out to Thread – and for your concern around the chemicals used in the recycling process – a deep understanding of impact from every step of processing is very important to us. We’re always happy to talk through this stuff and share some insight.

At Thread, every step of the production process is important to us. We pay close attention to the recycling process to make sure we are making ethical and responsible decision.

The Process: Mostly Mechanical

The recycling process to extrude rPET flake into fiber then into fabric is predominantly mechanical, as opposed to chemical. The rPET flakes are melted and the recycled plastic is then extruded into fiber before being woven or knitted into fabric.

Dyes and Finishes

The application of finished and dyes is where chemicals come into play. We carefully avoid treatments on several banned substances lists to ensure compliance with all of our customers (and to do what’s best for the planet) during these final stages. There are some dye technologies that have some very promising developments, which will lessen the environmental impact even further.

Further Certification

We also recently completed the Material Health Safety Certification process through the Cradle to Cradle Institute for our t-shirt jersey fabric. This process included breaking down each product used in the manufacturing down to the molecular level to ensure that our fabric isn’t causing human or ecological harm.

You can view our certification here:

Thread’s jersey knit fabric has received a bronze rating for the Material Health Safety Certification.

What We Learned – Antimony:

While our production processes passed certification standards, we learned about the issue of antimony and recycled polyester. Antimony is present in PET bottles (soda and water bottles) and can be released in the heating processes required for recycling the rPET into fiber.

Aside from having an intimidating name, chronic exposure to antimony through inhalation has been reported to result in lung damage, skin irritation and stomach problems, and has been linked to reproductive issues.

We conducted additional third party testing and, while antimony levels were very close to being under the 100 ppm that is required by the institute for higher ratings, we cannot ignore the presence of antimony in rPET. This resulted in a bronze rating.
While the finished recycled fiber itself presents no harm, we cannot score above a bronze rating because of the release of antimony in production processes. If you look through the Cradle to Cradle Certifications, you’ll notice that no recycled polyester yarns or fabric have scored above a bronze material health rating because of this issue.

Moving Forward

Theoretically, removing antimony from the rPET before extruding it into fiber should be possible. We are in the process of exploring this with a number of scientists and researchers who are familiar with this advanced chemistry. Theoretically, removing antimony from the rPET before extruding it into fiber should be possible. We are in the process of exploring this with a number of scientists and researchers who are familiar with this advanced chemistry. Finding a solution to the antimony puzzle is something I am personally very interested in. It’s presence in the manufacturing process limits some of the applications for up-cycling plastic bottles into polyester and other products.

Between the Material Health certification and the fact that our team personally spends time at every production point in our supply chain – I am confident that the production of Thread fabric is safe to the people and communities where it is processed.

Please do not hesitate to follow up with any further questions.


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