Polyurethane foams, the material used to make mattresses, car and furniture cushioning, and packaging, cannot be recycled. It is usually turned into carpet underlay, and after that, it’s off to the landfills, where it will sit for a thousand years.
Scientists at the University of California, San Diego have developed a polyurethane foam made from renewable biological materials, however, that breaks down in soil, compost, and even in the ocean. Bacteria and fungi consume the material for nutrition, they report in the journal Science of The Total Environment.
The high-performance foam can be used to make shoe soles, and earlier this year the researchers launched a company, Blueview, that is making fully biodegradable shoes.
Footwear does not necessarily come to mind when you think of plastic pollution. Modern shoes and sandals is made mostly of plastic-based materials, and of the over 24 billion pairs manufactured globally each year, most end up in landfills or incinerators. Footwear also makes up a large percentage of plastic waste that ends up in the world’s oceans.
To tackle this environmental burden, molecular biologist Stephen Mayfield and his colleagues used algae oil to make polyurethane foams, which they first reported two years ago. The foam meets the standards for footwear, and has a chemical structure that allows it to biodegrade. “First, petroleum comes from algae; it’s just fossil algae oil, and plastics come from petroleum,” Mayfield said in April. “So why not make plastics directly from algae oil?”
In compost and soil, the foams lost much of their mass in 12 weeks. The researchers found that several bacteria and fungi grew on the foams, using them as their carbon food source.
To test the material in ocean waters, the team submerged it near a pier at the Scripps Institution of Oceanography. They found a mix of marine organisms, both bacteria and fungi, formed colonies on the polyurethane foam and broke it down. “I was surprised to see just how many organisms colonize on these foams in the ocean,” Mayfield said. “It becomes something like a microbial reef.”
The researchers tracked the molecular and physical changes of the material using spectroscopy and electron microscopy. They found that the material started to degrade in as little as four weeks.
Then, the researchers identified microorganisms from six marine sites around San Diego that could break down and ingest the polyurethane foam.
Source: Natasha R. Gunawan et al. Biodegradation of renewable polyurethane foams in marine environments occurs through depolymerization by marine microorganisms. Science of The Total Environment, 2022.
Image credit: Daniel Zhen, Algenesis Inc.
