Researchers have created a plant-based, sustainable and scalable material that could replace single-use plastics in many consumer products.
Researchers at the University of Cambridge created a polymer film by mimicking the properties of spider silk, one of nature’s strongest materials. The new material is as strong as many common plastics in use today and could replace plastic in many common household products.
The material was created using a novel approach to assemble plant proteins into materials that mimic silk at the molecular level. The energy efficient method, which uses sustainable ingredients, results in a self-supporting plastic-like film that can be manufactured on an industrial scale. A “structural” color that does not fade can be added to the polymer and it can also be used to make water resistant coatings.
The material is compostable at home, while other types of bioplastics require industrial composting facilities to degrade. In addition, the material developed by Cambridge does not require any chemical modification of its natural building blocks, so it can degrade safely in most natural environments.
The new product will be marketed by Xampla, a Cambridge University spin-off company that develops alternatives to single-use plastics and microplastics. The company will launch a line of single-use sachets and capsules later this year, which can replace plastic used in everyday products like dishwasher tablets and laundry detergent capsules. The results are published in the journal Nature Communication.
For many years, Professor Tuomas Knowles of the Yusuf Hamied Chemistry Department at Cambridge has been studying the behavior of proteins. Much of his research has focused on what happens when proteins fold up or “misbehave,” and how that relates to human health and disease, primarily Alzheimer’s disease.
“We normally study how functional protein interactions keep us healthy and how irregular interactions are involved in Alzheimer’s disease,” said Knowles, who led the current research. “It was a surprise to discover that our research could also address a big sustainability problem: that of plastic pollution. “
As part of their protein research, Knowles and his group investigated why materials like spider silk are so strong when they have such weak molecular bonds. “We discovered that one of the key characteristics that gives spider silk its strength is that the hydrogen bonds are arranged evenly in space and at a very high density,” Knowles said.
Co-author Dr Marc Rodriguez Garcia, a postdoctoral researcher in Knowles’ group who is now responsible for R&D at Xampla, began to investigate how to replicate this regular self-assembly in other proteins. Proteins have a propensity for molecular self-organization and self-assembly, and plant proteins in particular are abundant and can be obtained sustainably as a by-product of the food industry.
“Very little is known about the self-assembly of plant proteins, and it is exciting to know that by filling this knowledge gap, we can find alternatives to single-use plastics,” said doctoral student Ayaka Kamada , first author of the article.
The researchers managed to replicate the structures found on spider silk using a soy protein isolate, a protein with a completely different composition. “Because all proteins are made up of polypeptide chains, under the right conditions we can make plant proteins self-assemble just like spider silk,” Knowles said. “In a spider, the silk protein is dissolved in an aqueous solution, which then assembles into an extremely strong fiber through a spinning process that requires very little energy.”
“Other researchers have worked directly with silk materials to replace plastic, but it’s still an animal product,” Rodriguez Garcia said. “In a way, we created ‘vegan spider silk’ – we created the same material without the spider.”
Any replacement of plastic requires another polymer – the two in nature that exist in abundance are polysaccharides and polypeptides. Cellulose and nanocellulose are polysaccharides and have been used for a range of applications, but often require some form of crosslinking to form solid materials. Proteins self-assemble and can form solid materials like silk without any chemical modification, but they are much more difficult to work with.
The researchers used soy protein isolate (SPI) as a test plant protein because it is readily available as a byproduct of soybean oil production. Plant proteins such as SPI are poorly soluble in water, which makes it difficult to control their self-assembly into ordered structures.
The new technique uses an environmentally friendly mixture of acetic acid and water, combined with ultrasound and high temperatures, to improve the solubility of SPI. This method produces protein structures with enhanced intermolecular interactions guided by the formation of hydrogen bonds. In a second step, the solvent is removed, which gives a film insoluble in water.
The material has performance equivalent to high performance engineering plastics such as low density polyethylene. Its strength lies in the regular arrangement of the polypeptide chains, which means that there is no need for chemical crosslinking, which is frequently used to improve the performance and strength of biopolymer films. The most commonly used crosslinking agents are not durable and can even be toxic, while no toxic element is required for the technique developed by Cambridge.
“This is the culmination of something we’ve been working on for over a decade, which is understanding how nature generates material from protein,” Knowles said. “We didn’t set out to solve a sustainability problem – we were motivated by curiosity about how to create strong materials from weak interactions.”
“The key breakthrough here is being able to control the self-assembly, so that we can now create high performance materials,” said Rodriguez Garcia. “It’s exciting to be a part of this journey. There is a huge, huge plastic pollution problem in the world, and we’re fortunate to be able to do something about it.”