Can superglue help fight the plastic crisis?
The world makes about half a billion tonnes of plastic every year and throws away nearly all of it. It ends up in the oceans, landfill and in incinerators. And for various reasons, recycling plastic is not simple. But Scott Phillips, from Boise State University, has come up with a way to turn an everyday substance that is much easier to recycle back to the starting material - into useful plastics. He can turn cyanoacrylate - otherwise known as superglue - into long polymer chains that can be made, with a mould, into any shape you want. Admittedly the mould itself needs to be made of plastic to stop the glue sticking but they're working on that one, and recycling it just involves adding some heat…
Scott - Plastics are great materials, but the issue is that they've been designed to last forever and we don't need most of them to last forever. So what we're trying to do is create ones that would have good properties as plastics, but that we could ultimately convert back to starting materials to recycle the plastics. In this case, we looked at super glue as a starting material for making that kind of plastic that we could easily recycle.
Chris - Before we talk about super glue, why are plastics hard to recycle? We do have a plastics recycling bin and you're urged to put your waste plastic in it, so someone must be doing something with it.
Scott - It's a separation problem. And that we have a really large mixture of plastics labels that are on the plastics, glues that are with them, paper, aluminum. There's a variety of things mixed in with that plastic waste. And then the plastic itself has additives, dyes to make color, other kinds of additives to give certain properties to the plastic. At the end of the day, what we really need to be able to do is separate out the individual materials within those plastics from everything else that's in that mix. And with the polymer that we've just published on. We've designed a way that helps to circumvent some of that separations problem,
Chris - Tell us what it is and what it's got to do with super glue then.
Scott - When you glue something together with super glue, you're actually making a polymer. So super glue itself is not a polymer, it's just a starting material that reacts with surfaces. And when it reacts, it forms polymers. What we wanted to do is ask the question of could we take that same starting material that's in super glue and be able to make really long polymers and convert it into a useful plastic? People haven't really looked at that because super glue sticks to everything, so you wouldn't necessarily look at making it into a plastic.
Chris - And how did you solve the problem?
Scott - There's multiple components there. One is figuring out what container we could use, which seems like a silly problem to have to solve, but it's super glue and it sticks to everything. And ultimately what my student, Alison Christie, found and discovered is that superglue doesn't stick well to certain kinds of plastics like polyethylene polypropylene Tupperware, as an example. She could do her reactions and make long polymers in Tupperware, which makes it really, really easy to make plastics. And then the cool part about it is you can make Tupperware like plastic in any shape. So we're, we're not only making the polymer and the plastic, but we're also shaping it into a desired shape during the polymerization.
Chris - What about when you want to do the magic thing we were talking about, which is to recycle this? How do you get the plastic to fall apart again?
Scott - Well, one of the interesting things about the polymer that's formed from superglue is if you heat it past a certain temperature, it will reverse, meaning the reaction goes in the opposite direction to starting materials. So we knew that happened. The question was, could we take really bulk plastics, so large plastic items, rather than something like a glue or take a large plastic item and be able to heat it up and have those polymers still break down back to starting material? And then could we collect the starting material cleanly? And then the even harder question is, could we do that in the presence of a really contaminated, dirty mixture of other plastic waste, which is what you would normally encounter in a real life scenario.
Chris - And can you do that? So if you were handed a mixed bag of recycling and it had some of your polymers in it, as well as what normally ends up in the recycle bin, you would be able to get out back to the starting point, what you had made?
Scott - We can, and so we demonstrated that. We actually took basically household waste and it had paper and aluminum and food residue and shampoo and toothpaste residue and all the things you would expect to be in there. And then we combined it with some of Alison's plastic, heated it up, and then ultimately at the temperature that we're using, the starting material becomes a gas. And so we can then collect that gas and separate it from everything else that's in that mixture, including the dirt and the ketchup and everything that's there. The yield there for that experiment was about 75% of the polymer converted back to starting material that we were able to recover. So it's not a hundred percent in that dirty context. If we remove the paper and a bunch of food residue and all those other components, then the yield goes up, into the low 90% range.
Chris - Presumably the irony hasn't escaped you that you do need some non-environmentally friendly plastic, you call it Tupperware, to make your new plastic <laugh>. Can you get around that?
Scott - Oh, I think we probably could. We have other research where we're taking existing plastics, ones that you can't easily recycle, and we're combining them all together and making some new materials out of that existing plastic. Now, whether we could completely get around it, that remains to be seen. That's a good question and something that we'll have to explore.