Technology · July 11, 2024

Here’s the problem with new plastic recycling methods

This article is from The Spark, MIT Technology Review’s weekly climate newsletter. To receive it in your inbox every Wednesday, sign up here.

Look on the bottom of a plastic water bottle or takeout container, and you might find a logo there made up of three arrows forming a closed loop shaped like a triangle. Sometimes called the chasing arrows, this stamp is used on packaging to suggest it’s recyclable. 

Those little arrows imply a nice story, painting a picture of a world where the material will be recycled into a new bottle or some such product, maybe forming an endless loop of reuse. But the reality of plastics recycling today doesn’t match up to that idea. Only about 10% of the plastic ever made has been recycled; the vast majority winds up in landfills or in the environment. 

Researchers have been working to address the problem by coming up with new recycling methods, sometimes called advanced, or chemical, recycling. My colleague Sarah Ward recently wrote about one new study where researchers used a chemical process to recycle mixed-fiber clothing containing polyester, a common plastic. 

The story shows why these new technologies are so appealing in theory, and just how far we would need to go for them to fix the massive problem we’ve created. 

One major challenge for traditional recycling is that it requires careful sorting. That’s possible (if difficult) for some situations—humans or machines can separate milk jugs from soda bottles from takeout containers. But when it comes to other products, it becomes nearly impossible to sort out their components. 

Take clothing, for instance. Less than 1% of clothing is recycled, and part of the reason is that much of it is a mixture of different materials, often including synthetic fibers as well as natural ones. You might be wearing a shirt made of a cotton-polyester blend right now, and your swimsuit probably contains nylon and elastane. My current crochet project uses yarn that’s a blend of wool and acrylic. 

It’s impossible to manually or mechanically pick out the different materials in a fabric the way you can by sorting your kitchen recycling, so researchers are exploring new methods using chemistry. 

In the study Sarah wrote about, scientists demonstrated a process that can recycle a fabric made from a blend of cotton and polyester. It uses a solvent to break the chemical bonds in polyester in around 15 minutes, leaving other materials mostly intact. 

If this could work quickly and at large scale, it might someday allow facilities to dissolve polyester from blended textiles, separating it from other fibers and in theory allowing each component to be reused in future products. 

But there are a few challenges with this process that I see a lot in recycling methods. First, reaching a large industrial scale would be difficult—as one researcher that Sarah spoke to pointed out, the solvent used in the process is expensive and tough to recover after it’s used.  

Recycling methods also often wind up degrading the product in some way, a tricky problem to solve. This is a major drawback to traditional mechanical recycling as well—often, recycled plastic isn’t quite as strong or durable as the fresh stuff. In the case of this study, the problem isn’t actually with the plastic, but with the other materials that researchers are trying to preserve.

The beginning of the textile recycling process involves shredding the clothing into fine pieces to allow the chemicals to seep in and do their work breaking down the plastic. That chops up the cotton fibers too, rendering them too short to be spun into new yarn. So instead of a new T-shirt, the cotton from this process might be broken down and used as something else, like biofuel. 

There’s potential for future improvement—the researchers tried to change up their method to disassemble the fabrics in a way that would preserve longer cotton fibers, but the reported research suggests it doesn’t work well with the chemical process so far. 

This story got me thinking about a recent feature from ProPublica, where Lisa Song took a look at the reality of commercial advanced recycling today. She focused on pyrolysis, which uses heat to break down plastic into its building blocks. As she outlines in the story, while the industry pitches these new methods as a solution to our plastics crisis, the reality of the technology today is far from the ideal we imagine. 

Most new recycling methods are still in development, and it’s really difficult to recover useful materials at high rates in a way that makes it possible to use them again. Doing all that at a scale large enough to even make a dent in our plastics problem is a massive challenge. 

Just something to keep in mind the next time you see those little arrows. 

Now read the rest of The Spark

Related reading

Read Sarah’s full story on efforts to recycle mixed textiles here

I wrote about several other efforts to recycle mixtures of plastic using chemistry in this piece from 2022

For a full account on the state of the hard problem that is the plastics crisis, check out this feature story

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