Polyethylene terephthalate (PET) is one of the most commonly manufactured plastics and has a wide range of uses in the packaging industry. It is also the most-talked-about plastics in waste recycling, and efforts to assist with PET biodegradations have been made.

The difficulty in depolymerising PET is due to limited access to ester linkages. It makes it difficult for ester bonds to be broken and therefore for the plastic to be broken down into its constituents.

Depolymerisation of PET can be achieved in chemical recycling facilities. Unfortunately, it has high processing costs which lead to PET primarily being recycled mechanically, if at all.

However, an accidental experiment has produced a mutant enzyme that degrades plastic more efficiently, eating through the plastic. The bacterium was discovered in 2016 at a waste recycling centre in Japan.

The enzyme, named PETase, was examined using X-ray crystallography, which allowed the researchers to create an ultra-high-resolution 3D model.

PETase has similar properties to a cutinase enzyme, but its active site where the substrate molecules bind, is up to three times the width that of cutinase, which allows the enzyme to accommodate the bulky components of PET.

The mutated enzyme resulted via the PETase and cutinase comparison process, where researchers studied the effects of PETase in a PET-containing environment, turned out to be more efficient at PET depolymerisation than the original form of PETase.

The new enzyme was also capable of degrading another type of plastic, polyethylene furandicarboxylate (PEF). PEF is a bio-based plastic produced from sugars and offers a greener alternative to PET.

The new technology, although in its early stages, could be useful for plastics recycling to address the global plastic waste issue and the increasing amount of discarded plastics through a chemical reaction. The impact of this process on the environment is still in discussion.

Find out more about PETase from thechemicalengineer.com.

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