When bananas really are green

By Nick Carne

Australian researchers have discovered a way to turn banana plantation waste into packaging material that they say is both recyclable and biodegradable.

Tests to date suggest that it can be used up to three times without any change to its properties, then breaks down in soil when it’s time to throw it away.

And there is no shortage of raw material given that bananas are one of the world’s most popular crops but only about 12% of each plant – the fruit – is used. The rest is waste.

“What makes the banana growing business particularly wasteful compared to other fruit crops is the fact that the plant dies after each harvest,” says chemical engineer Jayashree Arcot from the University of NSW.

“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.” {%recommended 9171%}

Arcot and chemist Martina Stenzel wondered whether pseudostems could be a source of cellulose for use in packaging, paper products, textiles and potentially medical applications such as wound healing and drug delivery.

The pair sourced banana plants grown from the Royal Botanic Garden in Sydney, extracted the pseudostem, dried it at very low temperatures then milled it into a very fine powder.

“We then take this powder and wash it with a very soft chemical treatment,” says Stenzel. “This isolates what we call nano-cellulose, which is a material of high value with a whole range of applications.” 

When processed, the material has a consistency similar to baking paper, the researchers say. It could be created at varying thicknesses, to suit a variety of format, from shopping bags to food trays.

Importantly, they add, tests with food showed there was no contamination risks.

“We tested the material with food samples to see whether there was any leaching into the cells,” Stenzel says. “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.”

Attention already has turned to other types of agricultural waste, with trials completed extracting cellulose from rice paddy husks and waste cotton gathered from cotton gins.

“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,” Stenzel says.