Scientists synthesized an improved hydrolase – an enzyme that breaks down up to 90 percent of PET (polyethylene terephthalate) into monomers in 10 hours. The properties of the resulting plastic are not inferior to those that were originally made from petroleum products, and can be used again for the manufacture of packaging and textiles, which will achieve a closed production cycle. The article was published in the journal Nature.

Every year, around 350 million tons of plastic are produced in the world, and about 200 million tons almost immediately become municipal solid waste, because they are used for a short period of time and are not further processed. One fifth of the world’s plastic is polyethylene terephthalate (PET) – this material is used to make textiles and packaging, mainly plastic bottles for water and carbonated drinks.

PET is a polyester and poorly hydrolyzed due to the high content of aromatic fragments of terephthalate. The most common way to process it is thermomechanical. Unfortunately, it leads to a loss of mechanical properties, and the quality of the material at the output is much lower than that of the original. Scientists have already described PET hydrolases – enzymes that can depolymerize PET and process it into new raw materials of good quality, however, all of them showed low productivity and were unprofitable.

French scientists led by Valérie Tournier of the University of Toulouse have begun searching for an advanced PET hydrolase. At the moment, they have completed the first stage of the project and have achieved effective processing of terephthalic acid, which accounts for the bulk of PET – 863 kilograms per ton of PET waste.

During the study, they treated commercial amorphous PET with various enzymes: BTA1 and BTA2 hydrolases of the soil bacterium Thermobifida fusca; the pathogen fungal cutinase Fusarium solani pisi; Gram-negative PETase Ideonella sakaiensis and LCC cutinase obtained from leaf compost leaves. They found that LCC is 33 times more effective than other enzymes and exhibits the highest thermal stability.

Next, scientists tried to further improve the enzymatic activity and thermal stability of LCC using protein engineering: chemical activity improved target mutagenesis of key amino acid residues, and thermal stability was improved by adding a disulfide bridge.

As a result, experts settled on the version of PET hydrolase, which breaks down 99.8 percent of terephthalic acid into monomers (which makes up 90 percent of PET waste) in 10 hours. At the same time, the cost of the enzyme necessary for processing one ton is only 4 percent of the price of a ton of primary PET. Plastic bottles for drinks have already been made from recycled raw materials, and in terms of properties they are not inferior to the original ones.

Here you can find out where to take PET bottles for recycling in Russia and what will happen to them after that. Earlier, we wrote that ships throw plastic bottles into the South Atlantic, ignoring the Convention on the Prevention of Pollution from Ships.