Carbios, a small French company that specializes in green chemistry, announced yesterday the recycling of waste polyester clothing into clear water bottles. This is exciting news because options for recycling of polyester or mixed-fiber clothing are very limited – usually limited to down-cycling rather than true recycling. I’ll get to the technology in a moment, but first a quick primer on polyester.
What is polyester?
Polyester is a generic name for a polymer that’s bridged by chemical bonds known as esters – the most common form is polyethylene terephthalate (PET), which is the basis for most plastic drink bottles (it’s labelled #1 in the plastic recycling scheme) and the most common textile, polyester. So, basically your disposable water bottle and polyester sweater are made from the same material and make up the majority of polyester in use. PET bottles can be recycled into new PET bottles, although even that’s not a straightforward process, especially when the waste stream is heavily contaminated. The waste stream contamination is partly why China decided to stop accepting large amounts of material from the West.
Recycling PET bottles is difficult enough, as it entails crushing, washing, separating, melting, and finally, drying the plastic pellets. So, you can imagine how much more difficult this is for waste clothing that contains a mix of several textiles (polyester blended with cotton, viscose, etc.) and a range of textile dyes and coatings. That’s why the Carbios news is exciting. Carbios estimates that up to 42 million tons of polyester clothing is produced annually. That’s equivalent to around 84 billion ugly Christmas sweaters – about 11 per person on the planet – every year. Aren’t we amazing that we churn out so much plastic and generate so much trash?!
How does Carbios recycle polyester?
Corbios made headlines earlier in the year with an article in Nature describing the enzymatic deconstruction of the PET polymer back to the original monomer, terephthalic acid. So, this is the crucial difference between conventional recycling and the approach that the Carbios researchers have taken – rather than trying to work with intact fibers they have broken it down to the original building blocks. This way, it’s possible to take on more contaminated waste streams such as mixed-fiber clothing, where the PET needs to be separated from the other fibers, dyes, and fabric coatings.
Here’s the complete abstract of their Nature paper in April, 2020:
Present estimates suggest that of the 359 million tons of plastics produced annually worldwide, 150–200 million tons accumulate in landfill or in the natural environment. Poly(ethylene terephthalate) (PET) is the most abundant polyester plastic, with almost 70 million tons manufactured annually worldwide for use in textiles and packaging. The main recycling process for PET, via thermomechanical means, results in a loss of mechanical properties. Consequently, de novo synthesis is preferred and PET waste continues to accumulate. With a high ratio of aromatic terephthalate units—which reduce chain mobility—PET is a polyester that is extremely difficult to hydrolyse. Several PET hydrolase enzymes have been reported, but show limited productivity. Here we describe an improved PET hydrolase that ultimately achieves, over 10 hours, a minimum of 90 per cent PET depolymerization into monomers, with a productivity of 16.7 grams of terephthalate per litre per hour (200 grams per kilogram of PET suspension, with an enzyme concentration of 3 milligrams per gram of PET). This highly efficient, optimized enzyme outperforms all PET hydrolases reported so far, including an enzyme from the bacterium Ideonella sakaiensis strain 201-F6 (even assisted by a secondary enzyme) and related improved variants that have attracted recent interest. We also show that biologically recycled PET exhibiting the same properties as petrochemical PET can be produced from enzymatically depolymerized PET waste, before being processed into bottles, thereby contributing towards the concept of a circular PET economy.
The principal investigator on the paper is Prof. Alain Marty (INSA Toulouse) who is also now Chief Science Officer at Carbios. The lead authors are researchers at the Toulouse Biotechnology Institute. For me, this is a key point of their paper:
Here we describe an improved PET hydrolase that ultimately achieves, over 10 hours, a minimum of 90 per cent PET depolymerization into monomers, with a productivity of 16.7 grams of terephthalate per litre per hour (200 grams per kilogram of PET suspension, with an enzyme concentration of 3 milligrams per gram of PET).
Demonstrating technology like this on a small scale is one thing, but scaling it up is often challenging. Their numbers on production rates (grams/liter/hour) and enzyme loading look promising to me. And most likely they are continuing to improve on the enzyme and process efficiency.
Carbios can now recycle polyester fabric
So the paper above describes technology that has been applied to recycling waste PET bottles into either new recycled PET (rPET) bottles or even rPET fabric. The Carbios press release, yesterday, was to announce the application of the same technology to accept waste polyester clothing as an input.
“This result demonstrates the extent of our technology’s possibilities: We can now produce transparent bottles from polyester textile waste or from post-consumer colored bottles. This works both ways – so we can also make a t-shirt from bottles or disposable food trays,” said Professor Marty.
“I am very proud that we successfully transformed polyester textile waste into clear bottles, which have identical properties as those made from virgin PET. This major innovation allows us to expand our sources of supply which, until now, consisted primarily of PET plastic waste”
Is Carbios an ethical investment?
I think that this technology could make an important contribution to our massive plastic waste problem. It goes without saying that we absolutely need to reduce the production of plastic – whether it’s by avoiding Nestlé’s bottled water or choosing clothing that’s made from more sustainable textiles. This is something that we should be already doing, and yet polyester production is only increasing and also forecast to increase further in coming years. The world badly needs an international agreement on plastics, like the Montreal Protocol for ozone-depleting gasses and the Kyoto Protocol and Paris Agreement on climate change. But we also need two other things to happen:
- Consumer avoidance of plastic for single-use applications and fast fashion.
- Better infrastructure and technology for plastics recycling.
The progress that Carbios made towards this second objective gives me hope for the future and I do believe it’s an ethical investment. I bought Carbios stock yesterday – it trades as ALCRB on the Euronext Growth Paris stock exchange and as COOSF in the US. I hope that this technology can be scaled up and implemented in a sustainable fashion (i.e., a closed-loop process, or something close to this). Carbios has a development agreement with Novozymes for producing the enzymes that enable recycling of the PET plastics and fibers. Here’s a one-minute video overview of Carbios from last December:
And here’s an interview from last year with deputy CEO, Martin Stephan, on a French business show:
Carbios: improved biodegradable PLA plastic
The second video, above, also mentions another technology from Carbios: biodegradable plastic that’s made from polylactic acid (PLA) that’s impregnated with enzymes that will break down the PLA polymer. So it’s a self-degrading bioplastic, designed for short-term applications. PLA plastic is already the most common type of compostable plastic – if you’ve ever had an iced coffee or beer in a compostable plastic cup it’s probably made from PLA – but breaking it down normally requires a lot of time or an industrial composter. The PLA with enzymes is designed by Carbios to break down more quickly, either in a home compost bin or a municipal composter. You can see more about that in this video – and note that the example shown is a plastic sheet used to cover the soil around a row of plants. A lot of commercial agriculture involves the use of plastic sheeting – this is something that’s seldom discussed but really needs a solution, and compostable PLA does make sense for this application. A topic for another post 🙂
Disclaimer: I own shares in Carbios (COOSF)