Researchers can break down the polymers and form valuable chemicals by adding carbon black to plastics and exposing the recyclate to light.

Black plastic has been subjected to much criticism of late, both deserved and undeserved.

Perennial complaints about how difficult it is to recycle black plastic deserve a mention. Automated sorting machines shine a range of light on plastics and use the reflections to identify some of the different base polymers. However, black pigments absorb almost all the light, making auto-sorting challenging.

In the undeserved criticism category, there was that fiasco late last year about how black plastic in cookware was dangerous to our health. It turned out that a simple math error had greatly overstated the risk. Hopefully, you didn’t replace all your cookware (like we did).

We could all start singing a different tune about black plastics shortly.

A dash of carbon black, and voilà: Chemicals that fetch $10/lb

Prof. Stache’s group at Princeton has found some remarkable recycling results using plastics that many tend to ignore: PVC and polystyrene. By taking the plastics, adding some carbon black, and exposing the mixture to light, the polymers break down and form valuable chemicals that can sell for $10/lb. or more.

This degradation occurs because the light is energetic enough to break chemical bonds, but some of the light is also absorbed by the carbon black, which, in turn, heats everything up. It’s like thermal degradation — aka pyrolysis or chemical recycling — but since the light plays an important role, it’s more appropriately called photothermal degradation.

Related: The Case of the Black Plastic Spatula

True upcycling

What’s neat about this process is that the chlorine in the PVC — usually a headache for chemical recycling — suddenly is desirable. It re-attaches itself to the degraded polystyrene, creating chemicals that are not just cheap hydrocarbons, but chemicals of real value. Even more good news: The process is robust enough that plasticizers don’t appear to affect the results. This truly is upcycling.

My biggest criticism of standard chemical recycling is that you are more or less returning the polymer to its starting chemicals. Going from hydrocarbon monomers to polymers back to hydrocarbon monomers doesn’t make economic sense, and the laws of thermodynamics are the great enforcer of this. You will never come out ahead. Don’t even try.

Photothermal degradation is different. The output is specialty chemicals that won’t end up as polymers, but other chemicals that fetch higher prices. I can get behind this.

Commercialization will take time and capital

Just don’t expect to see this in your neighborhood next week. The research is preliminary and minimal, if anything has been optimized. Reading the research article, I was really excited with the results. At the same time, the engineer in me is going nuts thinking about all the experiments needed to commercialize this. But I’m not dejected. Scaling this up doesn’t appear to require any technical breakthroughs. It will just take some time and capital. The path seems very straightforward (albeit long).

Then there are additional questions to get the mind reeling. What if you do this with PVC and PE? Or PP? Or PET? (Ah yes, the mantra of R&D people everywhere — more research is needed!)

It’s clearly time that we give black plastics a bit more respect. They’ve had this hidden superpower within them all this time, and we’re only now recognizing it. It would be fantastic if this led to a world where we stopped hearing about how difficult it is to recycle black plastic and, instead, heard how wonderfully it can be upcycled.

https://www.plasticstoday.com/advanced-recycling/black-plastic-isn-t-bad-in-fact-it-has-a-superpower