We all know just how much plastic waste has polluted the planet, from the oceans to marine life, the list goes on. Many of us play our part in the fight for sustainability in trying to recycle as much as we can. Unfortunately though, recycling isn’t as helpful as it seems. Roughly about 30% of the plastic that goes into ‘single-use’ plastic bottles gets turned into new plastic, and more often than not ends up as a lower strength version.
Certain environmentalists feel that abandoning the use of plastics entirely is key, whilst others place greater emphasis on the recycling of the material. Carbios, a sustainable plastics company, suggest that the strong, lightweight nature of the material is extremely useful and that true recycling is part of the solution. Researchers from Carbios have engineered a bacterial enzyme that breaks down 90% of that same plastic into its original chemical building blocks that can then used to create high-quality new bottles.
Polyethylene terephthalate (PET) is one of the world’s most frequently used plastics, with approximately 70 million tons manufactured annually. Whilst PET bottles are recycled in many places already, the current approach has many problems. For example, recycling companies often end up with a vast array of different colours of plastic. They use high pressures and temperatures to melt these down, producing a grey, black or dark coloured plastic starting material that few companies want to use in the packaging of their products. This recycled material is usually turned into carpets or other low-grade plastic fibres frequently end up in a landfill or get burned. All in all, it seems as if it’s not really ‘recycling’ at all.
To overcome this inefficiency, scientists have searched for enzymes in microbes that break down PET and other plastics. Back in 2012, researchers at Osaka University discovered one such enzyme in a compost heap. However, the enzyme known as leaf-branch compost cutinase (LLC), slowly breaks apart PET bonds only, and falls apart after a few days of working at 65°C – the temperature at which PET begins to soften and allows the enzyme to move into the polymer to reach the links it needs to break.
Alain Marty, the chief scientific officer at Carbios, teamed up with Isabelle Andre, an enzyme engineering expert at the University of Toulouse. They sought to modify the enzyme in order to maximise its’ efficiency. After hours of work and research, they tested their new mutant enzyme, discovering that it could break down 90% of the PET bottles in less than 10 hours. The researchers then used the terephthalate and ethylene glycol building blocks generated by the enzyme to generate new PET and produce plastic bottles that were just as strong as those made from conventional plastics, thus overcoming the limitations of the current recycling of PET bottles.
Whilst this is very exciting, there are still questions surrounding whether the enzyme will be an economically viable solution. One of the main advantages of the enzyme is that it has no difficulty in making pure PET chemical building blocks from a mix of plastics containing ones other than PET, and PET bottles of different colours. This is because, the enzyme only breaks bonds linking the two PET components, returning them to their original form, while ignoring dyes and other plastics in the mix.
This groundbreaking research is fascinating for environmentalists, and those in the fight against plastics and the sustainability industry. Whilst the enzyme cannot recycle other major types of plastics, such as polyethylene and polystyrene. If successful, it could help society deal with one of the most challenging plastic problems we face.