Researchers at Washington University in St Louis have taken inspiration from the humble leaf to create bioplastics that are both biodegradable and stronger by adding introduce cellulose nanofibers.
Society has long struggled with petroleum-derived plastic pollution and awareness of microplastics’ detrimental effects on food and water supplies has added further pressure to find alternatives. In response, researchers have been developing biodegradable versions of traditional plastics, or ‘bioplastics’. However, current bioplastics face challenges as well. Current versions aren’t as strong as petrochemical-based plastics and they only degrade through a high-temperature composting system. The new research claims to have solved both of these problems.
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Long before plastic, humans wrapped their food in leaves, which easily biodegrade due to an underlying structure of cellulose-rich cell walls. So WashU’s chemical engineers decided to add cellulose to the design of bioplastics.
‘We created this multilayer structure where cellulose is in the middle and the bioplastics are on two sides,’ said Joshua Yuan, the Lucy and Stanley Lopata professor and chair of energy, environmental and chemical engineering at the McKelvey School of Engineering. ‘In this way, we created a material that is very strong and that offers multifunctionality,’ he added.
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The technology emerged from working with two of the highest production bioplastics today. Yuan and colleagues used a variation of their leaf-inspired cellulose nanofibre structure to improve the strength and biodegradability of polyhydroxybutrate (PHB), a starch-derived plastic; they further refined their technique for polylactic acid (PLA).
The plastic packaging market is a US$23.5billion industry dominated by polyethylene and polypropylene, polymers made from petroleum that break down into harmful microplastics. The researchers’ optimised bioplastic, called Layered, Ecological, Advanced and multi-Functional Film (LEAFF), turned PLA into a packaging material that’s biodegradable at room temperature. Additionally, the structure allows for other critical properties, such as low air or water permeability, helping keep food stable, and a surface that is printable. This improves bioplastics’ affordability since it saves manufacturers from printing separate labels for packaging.
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‘On top of all of this, the LEAFF’s underlying cellulose structure gives it a higher tensile strength than even petrochemical plastics like polyethylene and polypropylene,’ explained Puneet Dhatt, a PhD student in Yuan’s lab.
The USA is uniquely positioned to dominate the bioplastics market and establish a ‘circular economy’ wherein waste products are reused, fed back into systems instead of left to pollute the air and water or sit in landfills.
Yuan hopes this technology can scale up soon and is looking for commercial and philanthropic partners to help bring the improved processes to industry. Competitors from Asian and European research institutions are working to develop similar technology. But US industries have an advantage due to the country’s vast agriculture system.
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‘The US is particularly strong in agriculture,’ Yuan said. ‘We can provide the feedstock for bioplastic production at a lower price compared to other parts of the world.’
The ‘feedstock’ Yuan is referring to are chemicals such as lactic acid, acetate or fatty acids such as oleate, products of corn or starch fermentation by microbes that serve as bioplastic factories.
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Pseudomonas putida, for instance, is a microbial strain widely used in the fermentation industry, including to produce a variety of polyhydroxyalkanoates, including PHB. McKelvey Engineering researchers have designed ways to convert various wastes, including carbon dioxide, lignin and food waste, into bioplastics using strains such as P. putida. With improved bioplastic design, Yuan’s research further fills in that loop, with a version of PHB and PLA that could be produced much more efficiently and degrade safely into the environment.
‘The United States has a waste problem, and circular reuse could go a long way to turning that waste into useful materials,’ Yuan said. ‘If we can ramp up our bioplastic supply chain, it would create jobs and new markets.’
The research has been published in Green Chemistry and Nature Communications.