The researchers, from the University of Cambridge, said the compostable polymer film is as strong as many common plastics and could be used in a variety of household products.
The material was created using a new approach for assembling plant proteins into materials which mimic silk on a molecular level. The energy-efficient method, which uses sustainable ingredients, results in a plastic-like free-standing film, which can be made at industrial scale. Non-fading 'structural' colour can be added to the polymer, and it can also be used to make water-resistant coatings.
“Other researchers have been working directly with silk materials as a plastic replacement, but they're still an animal product,” said research co-author Dr Marc Rodriguez Garcia. “In a way we've come up with 'vegan spider silk' – we've created the same material without the spider."
The team replicated the regular spacing and high density of hydrogen bonds in spider silk by using soy protein isolate, readily available as a by-product of soybean oil production.
“Because all proteins are made of polypeptide chains, under the right conditions we can cause plant proteins to self-assemble, just like spider silk,” said research leader Professor Tuomas Knowles. “In a spider, the silk protein is dissolved in an aqueous solution, which then assembles into an immensely strong fibre through a spinning process which requires very little energy.”
The new technique uses an environmentally friendly mixture of acetic acid and water, combined through ultrasonication and high temperatures, to improve the solubility of the protein isolate. This method produces structures with enhanced intermolecular interactions, guided by the hydrogen bond formation. In a second step the solvent is removed, which results in a water-insoluble film.
The material reportedly has a performance equivalent to high performance engineering plastics such as low-density polyethylene. Its strength lies in the regular arrangement of the polypeptide chains, meaning there is no need for chemical cross-linking, which is frequently used to improve the performance and resistance of biopolymer films. The most commonly used cross-linking agents are non-sustainable and can even be toxic, but no toxic elements are required for the Cambridge-developed technique.
“The key breakthrough here is being able to control self-assembly, so we can now create high performance materials," said Dr Rodriguez Garcia. “It's exciting to be part of this journey. There is a huge, huge issue of plastic pollution in the world, and we are in the fortunate position to be able to do something about it.”
The new material is home compostable, whereas other bioplastics require industrial composting facilities to degrade. The Cambridge-developed material also requires no chemical modifications to its natural building blocks before composting, so it can safely degrade in most natural environments.
The product will be commercialised by Xampla, a University of Cambridge spin-out company developing replacements for single-use plastic and microplastics. The company will introduce a range of single-use sachets and capsules later this year, which can replace the plastic used in everyday products like dishwasher tablets and laundry detergent capsules.
The research was published in Nature Communications.
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