How Biodegradable Polyurethane Could Solve the Microplastic Pollution Problem

Polyurethane is everywhere. From foam cushions and adhesives, to coatings and synthetic fibers, this versatile polymer is a significant presence in our daily lives. But there's a catch; while uses of polyurethane plastics offer many advantages, its non-biodegradable nature means it can stick around in the environment for a long time, contributing to the global microplastic pollution crisis that damages our ecosystems and our health.

However, a new study from a U.S. Department of Energy (DOE) Bioenergy Technologies Office (BETO) funded startup, Algenesis Corporation and the University of California San Diego has demonstrated the ability to formulate high-quality polyurethane products that generate no persistent microplastics. By utilizing some clever chemistry and sourcing oil from algae instead of petroleum, they can produce polyurethane plastics, including waterproof fabrics and cell phone cases, that biodegrade naturally in the environment. This is possible by formulating the polyurethane in a way so that microorganisms recognize it as a food source and completely consume the material. The chemical bonds formed in petroleum-based polyurethane are unrecognizable to these microorganisms and are left in the environment for decades, turning into harmful microplastics.

In the study, the Algenesis team compared their bio-based polyurethane plastic to a petroleum-based plastic by grinding the materials into fine microparticles and mixing them into compost. The team found that within just 200 days their bio-based sample had been completely consumed, leaving no trace of microplastics, whereas the petroleum-based sample was unchanged.

To demonstrate these results, the team performed three different experiments starting with a respirometry approach. When the microbes break down plastics and use it as a food, they release carbon dioxide (CO2), which the respirometer measures. These results were compared to the breakdown of cellulose, which is considered the industry standard. The plant-based polymer showed 75% theoretical biodegradation in about 150 days, nearly matching the results of a cellulose control.

Next, the team used a water flotation approach. Since plastics are not water soluble and they float, they can be scooped off the surface of water or captured on a filter during lab testing. At intervals of 90 and 200 days, almost 100% of the petroleum-based microplastics were recovered, meaning none of it had biodegraded. On the other hand, after 90 days, only 32% of the plant-based microplastics were recovered, showing that more than half of it had already biodegraded. After 200 days, only 3% was recovered indicating that 97% of it had been consumed.

The last measurement approach involved chemical analysis via gas chromatography/mass spectrometry (GCMS). This approach detected the presence of the monomers used to make the plastic, indicating that the polymer was being broken to the base chemicals that the microbes can recognize as food. Scanning-electron microscopy further showed how microorganisms colonize the biodegradable microplastics during composting.

Creating an eco-friendly alternative to petroleum-based plastics is only one part of the long road to viability. The ongoing challenge is to be able to use the new material on pre-existing manufacturing equipment that was originally built for traditional plastic, and here Algenesis is making progress. They have partnered with several companies to make products that use the plant-based polymers developed at the University of California San Diego, including Trelleborg for use in coated fabrics and RhinoShield for use in the production of cellphone cases. RhinoShield, one of the world’s top producers of phone cases will be launching a Soleic® injectable smartphone case made from these new plant-based thermoplastic polyurethane (TPU) materials. “RhinoShield is looking forward to teaming up with Algenesis to tackle the world’s plastic issue. We’re equally enthusiastic about establishing sustainable standards for the phone case industry,” said Eric Wang, CEO of RhinoShield.

The promise of high-quality yet biodegradable polyurethane plastics offers hope in the fight against microplastic pollution. By working with nature rather than against it, we can create a more sustainable future where our materials leave a positive impact on the planet and do not compromise our health.

Daniel B. Fishman is a technology manager with the Bioenergy Technologies Office at the U.S. Department of Energy, where he helps manage the portfolio of applied research projects focused on developing algal biofuels.