Over in Thailand, Rimping Supermarket wraps its groceries in banana leaves instead of using plastic packaging. A continent away in Australia, researchers at the University of New South Wales dig further down to mesh the banana plant’s stem into ‘bioplastic’ with the potential to make a range of items, including shopping bags and packaging trays for meat.
Bananas are technically berries, and are grown commercially by creating thousands of cuttings which are planted and grown, have their fruit harvested and then die back. After harvesting the bananas, the plant material is then largely discarded or composted. Only 12 percent of a banana plant (the fruit) is actually used, say UNSW’s School of Chemical Engineering Research Professors Jayashree Arcot and Martina Stenzel.
88% plant waste is itself is not unusual of course – we eat billions of tomatoes and again the plants are composted after a short life, but it was the usefulness of the banana plant pseudostem that caught the attention of the UNSW professors. They’ve been working on a project to ‘convert agricultural waste into something that might add value to the industry it came from’. It turns out that the layered fleshy part of the discarded banana plant trunk can produce nanocellulose which the researchers have spun into a film.
Speaking on a podcast for The Royal Botanic Garden Sydney, Professor Stenzel explained that the fibers of nanocellulose are tiny compared to ordinary cellulose, and that they have a large surface area that can be used for many applications.
Cellulose is nature’s plastic
Cellulose can be extracted from many other plants, such as rice paddy husks and cotton waste. Bananas are an ideal candidate for developing into nanocellulose because their pseudostems produce a large amount of workable material, and there’s a steady global supply as banana crops are harvested.
“We are able to modify the surface chemistry of this extracted compound so that we can develop different types of grades of the bioplastic,” said Professor Arcot, adding “When I say ‘grades’, I mean whether we want a very strong material, a very flexible material or whether we want it to be very hydrophobic, whatever is required.”
Bioplastic – biodegradable packaging
Once the material has been processed and made into an item it can be further recycled several times, and it is also completely biodegradable. “We’ve done some preliminary biodegradability tests and we’re very happy with it,” Professor Arcot told the Brisbane Times, “One of our PhD students proved that we can recycle this three times without any change in properties.”
The researchers tried burying their banana plastic in soil for six months and showed that it was disintegrating. The film is also non-toxic. We tested the material with food samples to see whether there was any leaching into the cells,” Stenzel said on the podcast. “We didn’t see any of that. I also tested it on mammalian cells, cancer cells, T-cells and it’s all non-toxic to them. So if the T-cells are happy – because they’re usually sensitive to anything that’s toxic – then it’s very benign.”
An industry partner is needed
“What we’re really wanting at this stage,” Professor Stenzel told listeners, “is an industry partner who can look into how this could be upscaled and how cheap we can make it.” – ultimately that’s the biggest challenge for banana based bioplastic, it may be more sustainable but petrochemicals are cheap and hard to compete with.
Earlier last year, Professor Arcott had urged Australia’s own banana producers to consider making use of the banana’s biostem waste. “There is huge promise here for the banana industry to use that waste; at the moment I believe the stems are cut up and thrown away,” she said.
The researchers think that it would make sense for the banana industry to begin the processing of the pseudostems into powder at their plantations (as 90% of the stem is water – which would increase the cost of transport), the dried powder could then be sold to packaging suppliers to make new bioplastic packaging for the food industry or even has potential medical applications.
As of January 2020 there has been interest in this project from banana growers in Western Australia and Queensland as well as the packaging industry in NSW. Early stage talks are ongoing.