Biocomposites - the Future for Plastics?

Chris - Now joining us, we have Paul Fowler on the line. He's from the Biocomposites Centre of Bangor University. He specialises in the design and study of biocomposite materials: that's things like bioplastics and bioresins. He's trying to help companies across the globe practice greener technology. Paul, what exactly is a biocomposite material?

Paul - It's a material that consists of two components, a matrix and a fibre reinforcement. Now in a biocomposite we look for the matrix and the fibre composite to be derived from natural materials.

Chris - The stats are that one trillion plastic bags get made all around the world every year and most of them probably end up in landfills. Are bioplastics something that could replace these plastic bags and will therefore break down and be better for the environment?

Paul - Bioplastics certainly would go some way towards remedying some of the problems of plastics in the environment. The issue around plastic bags is a contentious one and there is a school of thought that perhaps biodegradability isn't necessarily the way to go with plastic bags.

Chris - Why not?

Paul - I'm thinking in terms of the biodegradability of plastic and its inclusion into landfill where it may not degrade in an aerobic fashion but in an anaerobic fashion.

Chris - And that makes methane?

Paul - In which case it would make methane, yes. So the whole issue of biodegradability may, in fact, be a red herring. Unless the application you're putting the material to actually demands biodegradability.

Helen - Paul, I've got an email here from Lizzie Jones and she points out a particular issue. We're getting more of this potato/starch based packaging and cups. She's wondering what to do with them. Now you mentioned that maybe putting them in to landfill isn't going to be the best thing. Can we compost them at home? Our kerb-side collections say clearly not to put these plastics into the compost for waste (they certainly do that in Cambridge). Can we do that at home?

Paul - Well certainly, I think home composting is one way that packaging materials is going. Certainly starch-based materials should compost quite well. If you manage a compost heap in quite an active way and make sure you turn it: keeping it reasonably well topped-up with green matter as well.

Helen - Do you have any idea why council collections say 'don't put them in your green bin'?

Paul - Well I guess it's a question of where the material's going and how it's segregated. It's a question of really being absolutely aware of what material is made from and its ultimate degradation fate.

克里斯-保罗,如果我们可以直接切入正题what bioplastics are: how can you make a plastic out of a potato?

Paul - The active component is the starch that is rendered typically by adding a 'plasticiser'. The starch is then processed to make a film. The starch is a key polymer which is then transformed to make a plastic film.

Chris - So what is going on with that 'plasticiser' to make the starch molecules, which are potato-like, into something plastic and stretchy and flexible?

Paul - What is happening is that the starch granules are being de-structured by applying mechanical and heat forces to them in the presence of a plasticiser. That plasticiser may be water. The individual molecules become sort-of 'flexibalised'. The plasticiser slides in between them to enable the material to become plastic and film-like.

Chris - What could we do with this material?

Paul - Biodegradable plastics, as you are aware, have seen utility in food packaging and carrier bag applications. There's no reason why a bioplastic couldn't be injection-molded or thermoformed into things like caps for products such as deodorants or hairspray. The thermoformed things could be used to package meat or vegetables.

Chris - And there's no danger that my car bumper might dissolve when I put it in the carwash?

Paul - Hehe. That's an interesting question - there's lots of scope for modifying starches to make them less biodegradable. Then you can actually extend the life of the product, if you will, with modifications of other biomaterials to prevent them from being so biodegradable as they first appear.