Researchers from the University of San Diego are advancing their brand of renewable and biodegradable materials to create coated fabrics, patent leather, adhesives, flavors and fragrances. The team created methods to produce microalgae-based polyols that can be used to make polyurethane foams with waste oils from algae biomass.

Image from the research team's prior work, showing a student pouring polyurethane into a flip-flop mold.Source: Erik Jepsen/UC San Diego Publications

Algae is considered the best renewable resource for replacing fossil fuels and battling global warming without impacting food supplies. But algae contains small organic contaminants like photosynthetic pigments and other cofactors that have prevented their widespread use.

The team worked with oil from green microalgae called Nannochloropsis salina (N. salina). This is a common source of omega-3 fatty acids commonly sold as dietary supplements. They chose N. salina as their growing algae for large scale production because it has high production of eicosatetraenoic acid (EPA) and for its ability to grow the strain for high biomass content.

After omega-3 fatty acid production, more than 70% of the microalgae is typically thrown away or burned. The team created a way to purify and convert the waste into azelaic acid, the building block for flexible polyurethanes. Researchers converted the co-product of the azelaic acid, hypertonic acid, into food flavoring and fragrance.

To start their work, the team created a scalable and cost-effective way to improve the purity of algae oil with simple physical methods and saponification. Saponification is a process where oils react with sodium and potassium hydroxide to produce glycerol and fatty acid salt, or soap. They also identified multiple contaminants in the waste oil to be eliminated.

Microalgae contain a variety of metabolic components that are insoluble in water and freely soluble in algae oil when extracted. These pigments inhibit downstream reaction efficiency and their removal is key to successful production. There is a scalable process performed on the oils from multiple algal species to produce valuable monomers to create bio-based plastic. The valuable monomers are molecules that take part in a chain reaction to form polymers. This process resulted in an eco-friendly polyurethane foam.

Polyurethane foams have varying commercial applications, including flip flops, running shoe soles, mattresses, yoga pats and more. They also made a flavoring molecule that was valued at $500 per kilogram.

A paper on this development was published in Green Chemistry.