Bio-based plastics such as polylactic acid (PLA) were invented to help solve the plastic waste crisis, but they often end up making waste management more challenging. Because these materials look and feel so similar to conventional, petroleum-based plastics, many products end up not in composters, where they break down as designed, but instead get added to the recycling stream by well-intentioned consumers. There, the products get shredded and melted down with the recyclable plastics, bringing down the quality of the mixture and making it harder to manufacture functional products out of recycled plastic resin. The only solution, currently, is to try to separate the different plastics at recycling facilities. Yet even with the most high-end, automated sorting tools, some bio-based plastics end up contaminating the sorted streams.
Scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) and the Joint BioEnergy Institute (JBEI) are collaborating with X – the moonshot incubator led by Alphabet, Google’s parent company – to not only skip the problematic separation step, but also make the final product better for the planet.
The team has invented a simple “one pot” process to break down mixtures of petroleum-based and bio-based plastics using naturally derived salt solutions paired with specialized microbes. In a single vat, the salts act as a catalyst to break the materials down from polymers, large structures of repeating molecules bonded together, into the individual molecules called monomers, which the microbes then ferment into a new type of biodegradable polymer that can be made into fresh commodity products. The process is described in a One Earth paper published today.
“It’s sort of ironic because the purpose of using bio-based plastics is to be more sustainable, but it’s causing problems,” said first author Chang Dou, a senior scientific engineering associate at the Advanced Biofuels and Bioproducts Process Development Unit (ABPDU) at Berkeley Lab. Dou was recently named as one of the American Institute of Chemical Engineer’s 35 Under 35. “Our project is trying to get around the separation issue and make it so you don’t have to worry about whether you mix your recycling bin. You can put all the plastic in one bucket.”