Nanotechnology

The new biodegradable plastic can be composted in your backyard

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July 10, 2023

(Nanowerk News) We use plastic in almost every aspect of our lives. These materials are cheap to manufacture and very stable. The problem comes when we finish using something made of plastic — plastic can stay in the environment for years. Over time, plastic breaks down into smaller fragments, called microplastics, which can cause significant environmental and health problems.

The best solution is to use biodegradable bio-based plastics, but many of those bioplastics aren’t designed to degrade in backyard composting conditions. They must be processed in commercial composting facilities, which are not accessible in all areas of the country.

A team led by researchers at the University of Washington have developed a new bioplastic that degrades on the same time scale as banana peels in a backyard compost bin. This bioplastic is made entirely from powdered blue-green cyanobacteria cells, otherwise known as spirulina. The team used heat and pressure to shape spirulina powder into various shapes, the same processing techniques used to make conventional plastics. The UW team’s bioplastics have mechanical properties comparable to single-use plastics derived from petroleum.

The team published these findings in Advanced Functional Materials (“Making Strong and Rigid Bioplastics from Whole Spirulina Cells”).

“We are motivated to make bioplastics that are bio-derived and biodegradable in our backyard, while also being processable, scalable and recyclable,” said senior author Eleftheria Roumeli, UW assistant professor of materials science and engineering. The bioplastic we developed, using only spirulina, not only has a similar degradation profile to organic waste, but is also on average 10 times stronger and stiffer than the previously reported spirulina bioplastics. These properties open up new possibilities for the practical application of plastic-based spirulina in a wide range of industries, including single-use food packaging or household plastics, such as bottles or trays.”

Researchers chose to use spirulina to make bioplastics for several reasons. First, it can be cultivated on a large scale because people already use it for various foods and cosmetics. Also, spirulina cells absorb carbon dioxide as they grow, making this biomass a carbon-neutral, or potentially carbon-negative, feedstock for plastics.

“Spirulina also has unique flame retardant properties,” said lead author Hareesh Iyer, a UW materials science and engineering doctoral student. “When exposed to fire, it self-extinguishes immediately, unlike many traditional plastics which catch fire or melt. This flame retardant characteristic makes spirulina-based plastics advantageous for applications where traditional plastics may not be suitable due to their flammability. One example could be plastic shelves in data center because the systems used to keep servers cool can get very hot.”

Making plastic products often involves processes that use heat and pressure to shape plastic into the desired shape. The UW team is taking a similar approach with their bioplastic.

“This means that we don’t have to redesign the manufacturing line from scratch if we want to use our materials on an industrial scale,” says Roumeli. “We have removed one of the common barriers between the laboratory and scaling to meet industrial demand. For example, many bioplastics are made from molecules extracted from biomass, such as seaweed, and mixed with performance modifiers before being cast into films. This process requires materials in a form solution before casting, and it is not scalable.”

Other researchers have used spirulina to make bioplastics, but the UW researchers’ bioplastics are much stronger and stiffer than their previous efforts. The UW team optimized the microstructure and bonding in these bioplastics by changing their processing conditions — such as temperature, pressure and time in an extruder or hot-press — and studied the structural properties of the resulting material, including its strength, stiffness and toughness.

These bioplastics are not quite ready to be scaled up for industrial use. For example, although this material is strong, it is still quite brittle. Another challenge is that they are sensitive to water.

“You don’t want these materials to be exposed to rain,” says Iyer.

The team is working on this issue and is continuing to study the basic principles that determine how these materials behave. The researchers hope to design for different situations, by creating a variety of bioplastics. This would be similar to existing variations of petroleum-based plastics.

The newly developed material is also recyclable.

“Biodegradation is not our preferred end-of-life scenario,” said Roumeli. “Our spirulina bioplastic can be recycled through mechanical recycling, which is very accessible. However, people don’t recycle plastic very often, so it’s an added bonus that our bioplastic degrades quickly in the environment.”



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