Junk plastic turns into high-value commodity with chemistry trick

**Nick Petruchel** (0:24)
Welcome back to The Nature Podcast. This week, how to turn a plastic into a lubricant, and how a yeast can help make a cancer drug. I'm Maren Hunsberger, and I'm Nick Petruchel.
This week in Nature, researchers have shown that a common plastic can be turned into a lubricant rather than heading to landfill.
The plastic in question is polyvinyl chloride, better known as PVC. The poly may give you a clue to its structure, if you remember your high school chemistry. It's made up of hydrocarbons, carbon and hydrogen atoms, with a chlorine atom on the side, repeated many, many times in a long chain. This relatively simple structure belies how versatile it is, coming in harder and more flexible forms. That means it's everywhere. It's in pipes, doors, bottles, packaging, and probably in your pocket, as it's often the plastic of choice to make credit cards. But while it's useful for making a lot of products, there is the question of what to do with it at the end of its life. It can be recycled, but the process is difficult, and in many cases, the resulting recycled products aren't worth much more than the original PVC, meaning that a lot of it just ends up in landfill. This new work, though, may show a way to make a much more valuable product out of PVC, and therefore give an economic incentive to recycle it. That product? Lubricant. And by lubricant, I mean the kind you put in your car. This lubricant, often made from a chemical called poly-alpha-olefin, can fetch a price of 3,200 to 6,000 US dollars per metric ton. Much higher than the perhaps 1,000 dollars per metric ton that PVC is worth.
I called up Greg Liu, one of the authors behind this transformative work, to learn more about his lubricant making process. And he told me how he and his team got started in tackling PVC.

**Maren Hunsberger** (2:38)
So, the first, initially, we actually thought about, OK, can we use them to make a material?
But after a few years of trial and error, and we realized that actually it's very difficult to make those materials, especially to reuse them in the plastic field. Then we realized, OK, maybe we don't have to close the plastic loop to just use it as a new plastic, but we can turn into something else.

**Nick Petruchel** (3:00)
And so Charles, what is that idea? What did you want to do to not turn them into plastic, but to turn them into what else?

**Maren Hunsberger** (3:06)
At first, we were thinking about if it's polyvinyl chloride, if we can take all the hydrocarbon background, so maybe we can use it as a backbone for linkage. And if we can attach something else to that, then we may be able to make a cross-linked PE version of material.
The motivation is actually very simple, right? Because PVC is widely used in pipes. And nowadays, especially in Europe and in the United States, and there are more pipes made of cross-linked PE or XPE. So if we can take the old PVC pipes and make it into XPE, that means we can still use them in piping and similar applications.
So we tried a lot of times to make them into cross-linked materials, and we made some materials. It's some materials that potentially can be usable, but it's not the performance that we would like to be. And then we realize, okay, what if we break it down further? And what else we can do about it? And that's why we came up with the lubricant idea.

**Nick Petruchel** (4:06)
But the question, I suppose, is how does one turn PVC into said lubricant? So how did you actually go about doing it?

**Maren Hunsberger** (4:13)
So when we got the first experiment results from the attempt to make an XPE, we made some material that is like soft, very gooey, kind of tacky, and we don't know what to do with it. And if you made a reaction to go further, is it a little bit of whiskers? And then we realized, oh, it's a whiskers honey-like material.
So maybe that's not the best material for XPE, but it's a nice material for lubricant. And that's how we actually stumped on pound it.

**Nick Petruchel** (4:43)
Bit of serendipity there then, but I suppose that having this sort of gooey substance isn't quite a lubricant. So did you have to do more to actually get it to be a proper lubricant?

**Maren Hunsberger** (4:53)
Yes. So we have to do some more chemistry to make it happen. And then it becomes a question, maybe a bit more technical here now, is that we need to controllably break the chains in a way that we can attach some new molecules onto it, and then we can make some molecule in a range that's suitable for lubricants. And that's how we perform the systematic study, how do we tune the reaction conditions like temperature, time. All those are the downstream optimization process to make a high-quality lubricant.