A while ago we rejoiced in the widespread presence of bioplastics or bio-based plastics.  

Finally, there’s an alternative for oil-based plastics, we said. At last, we can improve plastic waste issues, we said. 

Yes, bio-based plastics like polylactic acid (PLA) were created to tackle the plastic waste crisis.  

Unfortunately, we’ve recently found out that they often complicate waste management.  

The main cause for this complication is the resemblance of PLA plastics to traditional petroleum-based ones. 

Because they look similar, most well-intentioned consumers unknowingly toss them into the recycling bin instead of composting. 

Despite consumers’ meticulous effort to separate plastics, the similarity between the two types of plastics becomes a drawback. 

This leads to a mix of plastics that’s challenging to process, hindering the production of functional recycled plastic items. 

So far, the only solution is to separate these plastics at recycling facilities.  

However, even with advanced automated tools, some bio-based plastics still find their way in sorted plastics. 

Scientists from Lawrence Berkeley National Laboratory and the Joint BioEnergy Institute have worked together. They’ve also collaborated with X—the moonshot incubator led by Alphabet, Google’s parent company. 

Together, they wanted to tackle this issue by taking a new approach. 

They’ve devised a straightforward “one pot” process. This process breaks down mixtures of petroleum-based and bio-based plastics using naturally derived salt solutions and specialized microbes. 

If you’d like, you can read more details about their discovery in One Earth paper. 

 

 

One pot process 

The scientists explained that in a single vat, the salts act as a catalyst. The salts then break down the plastics into individual molecules called monomers. 

Microbes then ferment these monomers into a new type of biodegradable polymer. And it’s not just flimsy polymer, it’s one that’s ideal for creating fresh commodity products. 

This streamlined process eliminates the need for separating different plastics, making recycling more efficient. 

First author Chang Dou said, “”It’s sort of ironic because the purpose of using bio-based plastics is to be more sustainable, but it’s causing problems.” 

Dou is a senior scientific engineering associate at the Advanced Biofuels and Bioproducts Process Development Unit at Berkeley Lab. The scientist was also 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,” Dou added. 

Aside from making recycling much simpler, this method could open doors to bio-based manufacturing of other valuable products. 

Using one-pot method to produce other things 

The team wants to continue using the same bacteria to process plastic monomers. They want to see a future where biofuels or medicines are made from plastic waste. That way, there’ll be less amounts of it just sitting in landfills or polluting the waters. 

Zilong Wang, a UC Berkeley postdoctoral researcher, said, “There is an open discussion on whether we can use waste plastics as a carbon source for biomanufacturing. It is a very advanced idea. 

“But we proved that using waste plastics, we can feed microbes. With more genetic engineering tools, microbes might be able to grow on multiple types of plastics at the same time. 

“We foresee the potential to continue this study where we can replace the sugars, traditional carbon sources for microbes, with the processed hard-to-recycle mixed plastics that can be converted to valuable products through fermentation.” 

So, the scientists want to experiment further with different organic salt catalysts. They want to find cost-effective and reusable options. 

Moreover, they’re exploring how the process would operate at the large scales of real-world recycling facilities. 

Their experiments have demonstrated the potential of the approach with mixtures of polyethylene terephthalate (PET) and PLA. 

The two are the most common petroleum-based and bio-based plastics. 

This one-pot process successfully broke down 95% of the mixture. It has also converted the molecules into a biodegradable polymer known as polyhydroxyalkanoate (PHA). 

It should be noted that the recycling process is currently proven for PET plastics contaminated with biodegradable PLA. 

However, the team believes it can adapt to various plastic streams encountered in real recycling facilities. 

Per the scientists, the potential economic viability and environmental benefits of this method are promising. They’re excited to develop this process further to provide solutions for sustainable plastics. 

 

 

Similar discovery by ORNL scientists 

The current problem of mixing plastics together is so well-known that other scientists want to tackle it, too. 

These plastics often end up in landfills or incinerated, contributing to environmental issues. That’s why folks at the Department of Energy’s Oak Ridge National Laboratory (ORNL) want to stop that. 

As we know, the current, conventional recycling process involves manually (or mechanically) separating plastics. Since that takes effort and money, facilities are reluctant to do it all the time. 

In response, the ORNL scientists developed a new catalytic recycling process. This process uses carefully planned chemical design, neutron scattering, and high-performance computing.  

Similar to the previous discovery, this process breaks down multiple polymers in mixed plastics into monomers. 

Published in Materials Horizons, the researchers found that their multipurpose catalyst outperformed using individual catalysts for each plastic type.  

The new catalyst demonstrated significant environmental benefits.  

Per the researchers, the benefits include up to 95% fewer greenhouse gases, up to 94% less energy input, and up to a 96% reduction in fossil fuel consumption. 

ORNL synthetic polymer chemist Tomonori Saito said, “Our approach involves a tailored synthetic organocatalyst — a compound comprised of small organic molecules that facilitate organic chemical transformations. 

“The organocatalyst can convert batches of mixed plastic waste into valuable monomers for reuse in producing commercial-grade plastics and other valuable materials.” 

 

 

The ambition to have a closed-loop recycling system 

With the efficient chemical processes by ORNL scientists and researchers from the first mentioned research, they could revolutionize plastic production. 

By establishing a closed-loop recycling system globally, it has the potential to reduce annual energy consumption by about 3.5 billion barrels of oil. 

Now, the ORNL process isn’t limited to a specific type of plastic. The scientists said that their new organocatalyst has proven effective in deconstructing various polymers. 

For instance, the catalyst could deconstruct safety goggles, foams, water bottles, and ropes or fishing nets. Altogether, those items make up over 30% of global plastic production. 

The process offers numerous environmental advantages by replacing harsh chemicals, providing good selectivity, thermal stability, nonvolatility, and low flammability. 

Moreover, it’s also effective against multicomponent plastics like composites and multilayer packaging. It’s a breakthrough that may greatly contribute to a more sustainable approach to plastic recycling. 

To confirm the formation of deconstructed monomers, the scientists used small-angle neutron scattering at ORNL’s Spallation Neutron Source. This offered them detailed structural insights at different levels. 

The organocatalyst operates at various temperatures to sequentially recover individual monomers in a reusable form.  

This allows for the conversion of mixed plastics polymers into true recycled plastics. 

In addition, the recovered monomers and organocatalyst are water-soluble, enabling easy extraction and reuse for multiple deconstruction cycles. 

Lead author Md Arifuzzaman highlighted the practicality of their approach.  

“The nearly pure monomers are then extracted, leaving the catalyst, which is almost entirely recovered by evaporating the water and can be directly reused for multiple deconstruction cycles,” Arifuzzaman said. 

 

Sources:

https://phys.org/news/2023-11-plastic-anxiety.html

https://www.ornl.gov/news/ornl-scientists-close-cycle-recycling-mixed-plastics