Researchers at the University of Washington have led the development of new bioplastics that apparently break down at the same rate as a banana peel in a home compost bin – a breakthrough hoped to prevent plastics from creating microplastic pollution if they escape recycling streams.

Most bio-based plastics currently available on the market are industrially recyclable, but this requires the materials to be sent to commercial composting facilities, which are not yet accessible throughout the United States. Nor are most bioplastics thought to be degradable in home composting processes.

As such, the new materials are said to offer biodegradability while offering the same mechanical properties as single-use plastics derived from petroleum. They are also said to be recyclable.

The bioplastics are made from blue-green cyanobacteria cells, or spirulina. Starting with a powder form, the team applied heat and pressure to form various shapes in a process similar to the production of conventional plastics.

“This means that we would not have to redesign manufacturing lines from scratch if we wanted to use our materials at industrial scales,” said senior author Eleftheria Roumeli, assistant professor of materials science and engineering at the University of Washington. “We’ve removed one of the common barriers between the lab and scaling up to meet industrial demand.

“For example, many bioplastics are made from molecules that are extracted from biomass, such as seaweed, and mixed with performance modifiers before being cast into films. This process requires the materials to be in the form of a solution prior to casting, and this is not scalable.”

It is believed that spirulina can be cultivated at a large scale due to its existing uses in various foods as cosmetics, meaning that its use in bioplastic production would not have negative effects on other supply chains. During their growth, spirulina cells are also said to sequester carbon dioxide in a carbon-neutral, and potentially carbon-negative, process.

“We were motivated to create bioplastics that are both bio-derived and biodegradable in our backyards, while also being processable, scalable and recyclable,” Roumeli continued. “The bioplastics we have developed, using only spirulina, not only have a degradation profile similar to organic waste, but also are on average 10 times stronger and stiffer than previously reported spirulina bioplastics.

“These properties open up new possibilities for the practical application of spirulina-based plastics in various industries, including disposable food packaging or household plastics, such as bottles or trays.”

“Spirulina also has unique fire-resistant properties,” added lead author and University of Washington materials science and engineering doctoral student Hareesh Iyer. “When exposed to fire, it instantly self-extinguishes, unlike many traditional plastics that either combust or melt.

“This fire-resistant characteristic makes spirulina-based plastics advantageous for applications where traditional plastics may not be suitable due to their flammability. One example could be plastic racks in data centres because the systems that are used to keep the servers cool can get very hot.”

Although this is not the first instance of bioplastics being created from spirulina, it claims to be the strongest and stiffest attempt so far. This is due to optimised microstructure and bonding within the plastics, the team explains; this was achieved by altering temperature, pressure, time in the extruder or hot-press, and other processing conditions, and examining the impact on the final material.

However, the team warns that the bioplastics are not yet industry ready. Despite being strong, the materials remain brittle and sensitive to water. Therefore, the researchers are continuing to study their findings and aim to create a range of bioplastics tailored for different applications, much like the variety in existing petroleum-based plastics.

Additionally, Roumeli went on to clarify that “[b]iodegradation is not our preferred end-of-life scenario. Our spirulina bioplastics are recyclable through mechanical recycling, which is very accessible. People don’t often recycle plastics, however, so it’s an added bonus that our bioplastics do degrade quickly in the environment.”

The team’s findings are available in the June 20 edition of Advanced Functional Materials.

At the end of last year, European Bioplastics predicted that the global capacity of bioplastic production will increase by 4.7 million tonnes in the lead-up to 2027.

Since then, biomaterials have been derived from various places. The European BeonNAT project claims to have extracted biomass from various types of wood for use in bioactive cosmetics, biochar, activated carbon, and pet litter with essential oils.

Spark Sourcing’s GEX bio-calcium, which is made from eggshells, has been granted a US patent that recognises the material as waste-saving and environmentally friendly, while the European Bio-Uptake project is set to develop bio-based intermediates to manufacture eco-container lids and other products.

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