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Japan accelerates hunt for plastics that rapidly biodegrade in the ocean

Yutaka Takeuchi (at left) an aquatic biologist at Kanazawa University, works on a tank he devised for accurate bioplastics biodegradation tests.© Kanazawa University

Stroll through the aisles of any Japanese conbini, or convenience store, and you’ll be struck by the staggering array of foods packed in plastics. It’s clear that treats, such as crisps and individually wrapped slices of cake, are very popular in the snack-loving nation.

But to biomaterial engineer Naoki Wada, they’re a symbol of a deep societal problem. “Food packaging in Japan is made of either plastic or paper coated with polyethylene plastic. These materials can’t be recycled, so they’re burned as garbage,” says Wada, who works at Kanazawa University, in central Japan, for a government-funded bioplastics initiative called COI-NEXT.

Japan is the second largest consumer of plastics per capita in the world, after the United States, with each person typically using 300-400 plastic bags per year. But plastics is also a global problem. Of the nearly 460 million tonnes of plastic that’s produced annually worldwide, only 9% is recycled, Wada points out. The rest is incinerated, dumped in the environment or buried in landfills, where it can take hundreds of years to degrade.

A poll in 2021 showed that there was an increasing desire within the Japanese population to see plastics pollution reduced. “Part of the solution is to replace plastics with bioplastics,” says Wada. In other words, swapping hard-to-recycle and slow-to-degrade plastics made using fossil fuels such as oil and gas, with those derived from plants and bacteria.

However, questions about the energy used to produce bioplastics, recyclability and biodegradability remain, which is one of the reasons a series of teams at different Japanese institutions and companies are tackling bioplastics from many angles as part of a project called COI-NEXT.

Recycling revolution

Wada is keen on developing a type of water-resistant bioplastic that could replace food-packaging plastics, such as those used for potato crisp packaging. “Our aim is to produce a biodegradable material that has moderate strength and stretchability, so that it can be used to replace existing products,” explains Gyanendra Sharma, an assistant professor in Wada’s lab.

The trick to making such a substance, the researchers say, lies in combining two types of long carbohydrate molecule chain, or polysaccharide. One polysaccharide is obtained from the dry or pulpy residue left after liquid has been extracted from agricultural products, such as grape skin and sugar beet, or other naturally occurring sugars. The other polysaccharide, known as bacterial cellulose nanofibre (BCNF), is composed of ultra-fine bundles of cellulose produced by certain strains of bacteria as a protective mechanism.

BCNFs are especially useful when it comes to making composites because their tangled structure and compatibility with other polysaccharides can help easily fine tune a material’s properties and make it more water-resistant and robust, for example, says Wada. Crucially, BCNFs can impart better recyclability and durability compared with glass, carbon and the other types of synthetic fibre commonly used to reinforce plastics today.

Composites made from BCNFs and various other substances, such as plant cellulose polysaccharides and polysaccharide esters, are biodegradable in soil and can be recycled a greater number of times without losing their strength, says Sharma.

Another important advantage offered by such composite materials is that, unlike conventional plastics, their production involves few chemicals that are hazardous or require a lot of energy to produce. Moreover, many polysaccharides and their esters, as well as the raw material bacteria feeds on, can be sourced from the agricultural waste. “That makes these bacterially produced composites more sustainable than plant-based fibres,” Wada points out.

Sharma adds: “It helps us fulfill one of our aims, which is to create wealth from waste without using wood, which is an already overused resource.”

Their team has devised a number of new techniques for producing such composites, including one involving suspending BCNFs in a solvent with a polysaccharide matrix, which is then evaporated to leave a layer of usable material.

Cellulose bioplastics can be created using agricultural by-products, such as banana plant fibre (top left) and leftover sugar-beet pulp (top centre) as raw materials. These bioplastics can then be used to create everything from yarn (top right) and filaments for 3D printing (bottom left) to toys (bottom centre) and packaging for cosmetics and toiletries (bottom right).© Kanazawa University

Biodegradability test

Another aspect to creating better bioplastics lies in helping them degrade quicker. For Yutaka Takeuchi, an aquatic biologist at Kanazawa University, that’s an insight that struck close to home.

“Our city has very nice beaches,” he explains. “But when I walk around the one in our neighborhood, I find a lot of small plastic spacers that are used in oyster farming.” They’re only required to separate farmed oysters for about three months, says Takeuchi, but they last indefinitely in the ocean, where they can be ingested by marine life.

Plastics currently comprise 80% of all waste in the ocean. The amount of plastic debris is expected to double over the next 15 years, and by 2050 the total weight of plastics in the world’s oceans could exceed that of fish.

Takeuchi is trying to find a solution to the problem of seafood farming waste, by creating biodegradable bioplastics for use in fisheries with a tropical coral biologist, Shinya Shikina, from the National Taiwan Ocean University. The initial goal is to create aquaculture tools, such as spacers and cable ties, made from bioplastics that will degrade within months.

To help other researchers in this endeavour, Takeuchi is also developing a better method for testing the biodegradeability of plastics in water.

Existing international bioplastics certifications are expensive and slow to obtain, he explains. Laboratories such as his, that make up to 50 bioplastics in a month, need answers more quickly, says Takeuchi.

So, he has devised a rapid test for biodegradability that places a thin film of bioplastic into a tank created to be a closed system containing diverse plants, microorganisms, plankton and fish, and recreating real world water temperature and salinity.

After one to three weeks, he assesses whether the plastic has been degraded by the bacteria and zooplankton present in the tank by measuring the amount of carbon dioxide produced, the activity level of the bacteria-produced cellulase enzymes present, or by staining the film and observing it under a microscope.

“The test is quick and it can be done anywhere, even the small aquarium tanks found in the corner of most classrooms in Japan,” says Takeuchi, whose team recently applied to patent their invention as a “quick and easy biodegradation test for younger generations to learn from”.

He hopes that the simplicity of the test will speed up innovation, that bioplastics will help reduce the use of oil and fossil fuel derived plastics, and that children begin to see fewer snack packets and oyster spacers on Japan’s beaches.

This work is part of the COI-NEXT initiative, which is being led by Kanazawa University with government support from the Japan Science and Technology Agency. Find out more here.

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