US researchers create fast-degrading spirulina-based bioplastics and emphasize importance of recycling

24 Jul 2023 --- Researchers from the University of Washington (UW), US, have developed new bioplastics made from spirulina that they claim degrade in approximately three to four weeks – the same rate as a banana peel in a backyard compost bin.

The team used heat and pressure to form the spirulina powder into various shapes – the same processing technique used to create conventional plastics. The material is also recyclable, which the researchers say may be a better end-of-life solution for the material than letting it biodegrade. 

“Biodegradation 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, so it’s a bonus that our bioplastics degrade quickly in the environment,” says Eleftheria Roumeli, senior author and UW assistant professor of materials science and engineering.

“The bioplastics we have developed have a degradation profile similar to organic waste and are, on average, ten times stronger and stiffer than previously reported spirulina bioplastics. These properties open up new possibilities for applying spirulina-based plastics in various industries, including disposable food packaging or household plastics like bottles or trays.”

Replacing conventional plastic 
Spirulina was used because it can be cultivated on large scales and is already used for various food and cosmetics applications. Additionally, spirulina cells sequester carbon dioxide as they grow, making this biomass a carbon-neutral, or potentially carbon-negative, feedstock for plastics.

Researchers from UW use powdered spirulina cells to create compostable bioplastic. “Spirulina also has unique fire-resistant properties,” says lead author Hareesh Iyer, a UW materials science and engineering doctoral student. “When exposed to fire, it instantly self-extinguishes, unlike many traditional plastics that 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 centers because the systems that are used to keep the servers cool can get very hot.”

The team created the bioplastic to combat the harmful effects petroleum-based plastics can have on people and the environment. “It can persist in the environment for years. Over time, plastic will break down into smaller fragments, called microplastics, that can pose significant environmental and health concerns,” they write. 

Current scalability 
Other researchers have used spirulina to create bioplastic. But the UW researchers say their bioplastics are stronger and stiffer than previous attempts. 

This is achieved by optimizing the microstructure and bonding within these bioplastics by altering their processing conditions – such as temperature, pressure and time in the extruder or hot press – and studying the resulting materials’ structural properties, including their strength, stiffness and toughness.

The spirulina bioplastic is firm but still relatively brittle and water-sensitive. The team says their bioplastic is still being prepared to be scaled up for industrial usage but can be more easily implemented into existing manufacturing lines.

" We would not have to redesign manufacturing lines from scratch if we wanted to use our materials at industrial scales,” explains Roumeli. Mallory Parker, UW materials science and engineering doctoral student, demonstrates that the bioplastic does not melt or catch fire.

“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 before casting, and this is not scalable.”

The scientists will continue to study the fundamental principles that dictate how these materials behave. The researchers hope to design for different situations by creating an assortment of bioplastics – similar to the variety of existing petroleum-based plastics.

The study is published in Advanced Functional Materials.

Finding the best solution
A recent survey found US consumers are failing to correctly dispose of compostable packaging due to ineffective on-pack labels, even when they have home access to curbside organic collections. Up to half of respondents are confused by look-alike packaging made of non-compostable materials and how to distinguish between packaging labeled “biodegradable” and “compostable.”

“The best-case solution would be to use bio-based plastics that biodegrade instead, but many of those bioplastics are not designed to degrade in backyard composting conditions. They must be processed in commercial composting facilities, which are not accessible in all regions of the country,” asserts the team.

The research reflects the ongoing debate in the packaging industry of which type of packaging results in the best waste management – biodegradable, recyclable or reuse. 

On the side of reuse, The Rethink Plastic alliance and a coalition of 81 organizations argue that using reusable takeaway packaging is a better solution for the food-packaging sector, from reducing emissions to pushing consumers and businesses toward a circular economy. 

Contrarily, DS Smith reported that proposals to increase mandatory packaging reuse in the EU could result in a massive rise in plastic use and backtrack years of progress. 

By Sabine Waldeck