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BIOPLASTICS | MATERIALS


Banking on a green future


Research into new types of bioplastic continues – with everything from wood pulp to fish gelatin being considered as possible starting materials. Lou Reade reports


Bioplastics continue to be the most hotly re- searched area of polymers. Sustainable sources of monomers – including soy, wood and even mango peels – continue to be identified. And, while bioplastics still account for a fraction of total plastics production, output is growing due to demand in a range of applications – especially packaging and agriculture. Researchers at Cambridge University have used their knowledge of ‘protein folding’ to create a bioplastic that could replace conventional plastics in many consumer products. They used a new approach to assemble plant


proteins into materials that mimic spider silk on a molecular level. This results in a plastic-like, free- standing film that can be produced on an industrial scale. The polymer can be coloured, as well as being used to make water-resistant coatings. The material is home compostable, while many bioplastics require industrial composting facilities to degrade. In addition, it requires no chemical modifications to its natural building blocks – so can safely degrade in most natural environments. The product will be commercialised by Cam- bridge University spin-out company Xampla. It will introduce a range of single-use sachets and capsules this year, which can replace the plastic used in products such as dishwasher tablets and laundry detergent capsules. The research was reported in Nature Communications. “We normally investigate how functional protein


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interactions allow us to stay healthy and how irregular interactions are implicated in Alzheimer’s disease,” said Tuomas Knowles, professor of physical chemistry and biophysics, who led the research. “It was a surprise to find our research could also address a big problem in sustainability: that of plastic pollution.” As part of their protein research, Knowles and


his group became interested in why materials like spider silk are so strong when they have such weak molecular bonds. “We found that one of the key features that gives spider silk its strength is the hydrogen bonds are arranged regularly in space and at a very high density,” he said. Proteins are known to undergo molecular


self-organisation and self-assembly. However, this process is not well understood for plant proteins. “It’s exciting to know that by filling this knowledge gap we can find alternatives to single-use plastics,” said Ayaka Kamada, a co-author on the paper. The researchers replicated the structure of spider silk using soy protein isolate (SPI) – a plant protein that is a by-product of soybean oil production. Plant proteins such as SPI are poorly soluble in water, making it hard to control their self-assembly into ordered structures. The new technique uses a mixture of acetic acid and water – combined with ultrasonica- tion and high temperatures – to improve SPI solubility. This produces protein structures with enhanced inter-molecular interactions. In a second step, the


July/August 2021 | FILM & SHEET EXTRUSION 13


Main image: Cambridge University researchers have identified a bioplastic modelled on spider silk


IMAGE: CAMBRIDGE UNIVERSITY


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