WASTE banana plant stalks could be turned into biodegradable and recyclable shopping bags.
Two researchers at UNSW Sydney are exploring a way to turn banana plantation waste into packaging material that is both biodegradable and recyclable.
Associate Professor Jayashree Arcot, UNSW School of Chemical Engineering and Professor Martina Stenzel, UNSW School of Chemistry were looking for ways to convert agricultural waste into something that could add value to the industry it was a byproduct of, while potentially solving problems for another.
According to Associate Professor Arcot, the banana industry produces large amounts of organic waste, with only 12 per cent of the plant being used (the fruit) while the rest is discarded after harvest.
"What makes the banana growing business particularly wasteful compared to other fruit crops is the fact that the plant dies after each harvest," Associate Professor Arcot said.
"We were particularly interested in the pseudostems - basically the layered, fleshy trunk of the plant which is cut down after each harvest and mostly discarded on the field.
"Some of it is used for textiles, some as compost, but other than that, it's a huge waste."
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Associate Professor Arcot and Professor Stenzel wondered whether the pseudostems would be valuable sources of cellulose - an important structural component of plant cell walls - that could be used in packaging, paper products, textiles and even medical applications such as wound healing and drug delivery.
Using a reliable supply of pseudostem material from banana plants grown at the Royal Botanic Garden Sydney, the duo set to work in extracting cellulose to test its suitability as a packaging alternative.
"The pseudostem is 90pc water, so the solid material ends up reducing down to about 10pc," Associate Professor Arcot said.
"We bring the pseudostem into the lab and chop it into pieces, dry it at very low temperatures in a drying oven, and then mill it into a very fine powder."
Professor Stenzel said they took this powder and washed it with a very soft chemical treatment.
"This isolates what we call nano-cellulose which is a material of high value with a whole range of applications," she said.
"One of those applications that interested us greatly was packaging, particularly single-use food packaging where so much ends up in landfill."
When processed, the material has a consistency similar to baking paper.
Associate Professor Arcot said depending on the intended thickness, the material could be used in a number of different formats in food packaging.
"There are some options at this point, we could make a shopping bag, for example," she said.
"Or depending on how we pour the material and how thick we make it, we could make the trays that you see for meat and fruit.
"Except of course, instead of being foam, it is a material that is completely non-toxic, biodegradable and recyclable."
The researchers have confirmed in tests the material breaks down organically after putting "films" of the cellulose material in soil for six months.
The results showed the sheets of cellulose were well on the way to disintegrating in the soil samples.
"The material is also recyclable. One of our PhD students proved that we can recycle this for three times without any change in properties," Associate Professor Arcot said.
Tests with food have proved that it poses no contamination risks.
"We tested the material with food samples to see whether there was any leaching into the cells," Professor Stenzel said.
"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."
Other uses of agricultural waste that the duo have looked at are in the cotton industry and rice growing industry - they have extracted cellulose from both waste cotton gathered from cotton gins and rice paddy husks.
"In theory you can get nano-cellulose from every plant, it's just that some plants are better than others in that they have higher cellulose content," Professor Stenzel said.
Associate Professor Arcot said what makes bananas so attractive in addition to the quality of the cellulose content was the fact they were an annual plant.
The researchers say for the banana pseudostem to be a realistic alternative to plastic bags and food packaging, it would make sense for the banana industry to start the processing of the pseudostems into powder which they could then sell to packaging suppliers.
"If the banana industry can come on board, and they say to their farmers or growers that there's a lot of value in using those pseudostems to make into a powder which you could then sell, that's a much better option for them as well as for us," Professor Arcot said.
And at the other end of the supply chain, if packaging manufacturers updated their machines to be able to fabricate the nano-cellulose film into bags and other food packaging materials, then banana pseudostems stand a real chance of making food packaging much more sustainable.
"What we're really wanting at this stage is an industry partner who can look into how this could be upscaled and how cheap we can make it," Professor Stenzel said.
Associate Professor Arcot said she thought the packaging companies would be more willing to have a go at this material, if they knew the material was readily available.