Lignin a possible basis for new bioplastics

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Saturday 5 October 2019 12:37PM (view full episode)

Lignin is a polymer found in wood and all plant material. It is tough and allows tall tress to support themselves. As we produce sugar, rice, wheat and other grains, there are enormous quantities of plant waste. Tim Bugg is investigating ways of using this waste as a basis for new chemical processes producing bioplastics. Unlike plastics produced from petrochemicals, bioplastics would be biodegradable and not bring with them the environmental problems associated with current plastics.

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Robyn Williams: Now we return to the place The Science Show visited last week, Warwick University, where Tim Bugg is Professor of Chemistry.

And, Professor Bugg, we're here to talk about lignin, and am I right or wrong, that table is made substantially of lignin.

Tim Bugg: Well, it is one of the components of wood, so wood probably has about 30% lignin. It also contains cellulose, about 50%, and hemicellulose. But all plant biomass has got lignin, may 20% to 30% in it.

Robyn Williams: What is lignin, in fact, chemically?

Tim Bugg: It's a polymer made up of units, which are aromatic rings, and then three carbons. But then they're linked together in different ways. Most biological polymers are regular; they have a very regular repeating unit. Lignin is a bit irregular in that the units are linked together in different ways. But the linkages are either carbon-oxygen ether bonds, or carbon-carbon bonds, which are very hard to break down. So lignin is very tough material. It's evolved to be very tough, to hold plants up. But we're now trying to break it down, which makes it very challenging.

Robyn Williams: And there's lots of it around, because whether we're in big cities or even in the country there's lots of waste that comes from old wood, from papers and god knows what else. So you're trying to make use of this vast supply, are you?

Tim Bugg: Yes, there is lots of lignin around. So there's agricultural waste, in the UK wheat is our major crop, so there's plenty of wheat straw around that could be used for biotransformation. Other countries have got other feed-stocks: rice, et cetera, sugar cane. But it's also a by-product of certain industries. The pulp and paper industry, for example, in Scandinavia, produces a lot of lignin as a by-product which currently they burn for energy. It's a bit like brown coal. But if we could convert it into high value chemicals that would be sustainable and be a very good thing to do.

Robyn Williams: One of the problems, though, surely, if something is so enduring, is the amount of energy you have to put in to break it down to make it useful—makes it counterproductive?

Tim Bugg: Makes it more difficult, certainly. So people have been trying to break down lignin for a number of years and it hasn't translated yet into a commercial process. Energy input maybe, we probably haven't quite got to that stage yet. We're still at the point of trying to get the yield to where it might be industrially important. I think using biological fermentation, probably the energy input would be not a serious problem. There also are people who are doing chemocatalysis on lignin that might be more of an issue for them.

Robyn Williams: If you were doing fermentation, how long would it take and how quickly could you get a yield?

Tim Bugg: Yeah, so our studies that we've published, we've shown that using genetically modified strains we can generate vanillin and pyridine dicarboxylic acids which are bioplastic precursors, but that takes typically seven days to do. So the lignin degradation is rather slow; so as well as the yield being modest, the fermentation time is quite slow. So we need to improve both of those two things, and our more recent strains were faster than that but we need to get down to between 24 and 48 hours.

Robyn Williams: But what's the payoff? I know you've got an awful lot of lignin there to make use of, would it be useful on a scale if you can solve those chemical problems you mention?

Tim Bugg: Yeah, we think so. One of the projects that we're working on is trying to make monomers to make new bioplastics. So I have a collaboration with Biome Bioplastics, a small biotech company based in Southampton, and they've shown that they can take those pyridine dicarboxylic acids and make a new bio-based plastic from that, which is used to make drinks bottles and also other kind of polymers like PBAT.

There's a lot of interest now in making new bioplastics, which are bio-based, they come from a renewable source, but they're also biodegradable, so compostable. And I think there is a big demand for new polymers with those characteristics, and we believe that these new materials would meet those criteria. But there are challenges ahead to get the yield up to what would be industrially relevant, to actually get it working at scale, and then the marketing of those materials.

Robyn Williams: It's interesting that we had on The Science Show a few years ago something from York. And this was an approach of using the vast amount of orange peel waste in a similar sort of way. Are you in touch with the York people in any way, in that regard?

Tim Bugg: Well, I know other people at York, probably not those particular people. There is a lot of food waste around, and that is another possible resource. Any kind of lignocellulosic material contains lignin. But it's possible, and certainly people are interested in that.

Robyn Williams: And the payoff could be enormous.

Tim Bugg: Yes. At the moment people pay you to take the waste away.

Robyn Williams: Tim Bugg is Professor of Chemistry at Warwick University in the UK.


Tim Bugg
Professor of Biological Chemistry
The University of Warwick
Coventry UK


Robyn Williams
David Fisher

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  • richard le sarcophage :

    06 Oct 2019 6:39:07pm

    What an advance, fifty years too late. Pity it will require 'The Market' to see sufficient profit, their one and only God, in it, for it to be put into practise. Oh, and the hydrocarbon plastics industry will fight it, tooth and nail, as is their commercial right in our glorious 'Free World'.