Scientists have synthesized an improved hydrolase — an enzyme which breaks down to 90 percent of PET (polyethylene terephthalate) to the monomers for 10 hours. Obtained plastic properties not inferior to what was produced from the petroleum products initially, and can be used again for the manufacture of packaging and textiles, which will allow us to achieve a closed production cycle. Article published in the journal Nature.
Every year the world produces approximately 350 million tons of plastics and 200 million tons almost immediately become solid waste, because they are used for a short period of time and then do not are recycled. One-fifth of the world accounts for the plastic polyethylene terephthalate (PET) — the material used for the manufacture of textiles and packaging, mainly plastic bottles for water and carbonated beverages.
PET is a complex polyester and is resistant to hydrolysis because of the high content of aromatic fragments terephthalate. The most common way of processing — thermomechanical. Unfortunately, it leads to loss of mechanical properties and material quality is much lower than the original. Scientists have already described PET-hydrolases — enzymes that can depolymerize the PET and recycle it into new raw materials of good quality, however, they showed poor performance and was unprofitable.
French scientists headed by Valerie Tournier (Tournier Valérie) from the University of Toulouse began the search for improved PET-hydrolases. At the moment they have completed the first phase of the project and achieved an effective processing of terephthalic acid, which accounts for the bulk of PET — 863 kilograms in one tonne of PET waste.
In the study, they were treated with a commercial amorphous PET different enzymes: hydrolase BTA1 and BTA2 soil bacterium Thermobifida fusca; cucinati pathogenic fungus Fusarium solani pisi; Patati gram-negative bacterium Ideonella sakaiensis and cucinati LCC obtained from leaf compost leaves. They discovered that LCC is 33 times more effective than other enzymes and demonstrates the high thermal stability.
Next, the researchers tried to further improve enzyme activity and thermostability LCC using protein engineering: chemical activity of improved targeted mutagenesis of key amino acid residues, and the thermal stability was improved by adding a disulfide bridge.
In the end, the specialists chose a version of PET hydrolases, which cleaves 99.8 percent terephthalic acid monomers (and this is 90 percent of PET-wastes) in 10 hours. The cost of the enzyme required for processing of one ton , is only 4 percent of the price of a ton of primary PET. From recycled materials they had already manufactured plastic beverage bottles, and properties are not inferior to original.
Here you can learn where to recycle PET bottles for reprocessing in our country and what happens to them after that. Previously, we wrote about the fact that the ships are thrown into the South Atlantic plastic bottles, ignoring the Convention for the prevention of pollution from ships.