Bio-based plastics, or bioplastics, which are made from more renewable sources were designed to help with plastic pollution. While they are not necessarily biodegradable or compostable, they do pose a peculiar problem when it comes to waste management at recycling centers.
Now, researchers 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 fix this issue.
According to researchers, since bioplastics 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 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 biobased plastics end up contaminating the sorted streams," a press release from Berkeley Lab explains.
The researchers have devised 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 release explains. The process was described in a paper published recentlyin the journal One Earth.
In the paper, the researchers demonstrated the potential of their approach in laboratory bench-scale experiments with mixtures of polyethylene terephthalate (or PET) – this is the most common petroleum-based plastic, used in things like water bottles and spun into polyester fibers – and PLA, the most common bio-based plastic. The Berkeley Lab release adds: “They used an amino-acid-based salt catalyst previously developed by colleagues at JBEI and a strain of Pseudomonas putida engineered by scientists at Oak Ridge National Laboratory. This combination successfully broke down 95% of the PET/PLA mixture and converted the molecules into a type of polyhydroxyalkanoate (PHA) polymer.”
“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,” Chang Dou, a senior scientific engineering associate at the Advanced Biofuels and Bioproducts Process Development Unit (ABPDU) at Berkeley Lab, said in the release.
The next step, according to the release, is to experiment with other organic salt catalysts to try to find one that is both highly effective at breaking polymers down and can be reused in multiple batches to lower costs. The researchers are also modeling how the process would work at the large scales of real-world recycling facilities.
According to the UN Environment Programme less than 10% of plastic waste is recycled, while at least 14 million tonnes end up in oceans every year, as per data from the International Union for Conservation of Nature.