Degradable plastic bottles ten hours, the decomposition rate up to 90%

Global annual production of 359 million tons of plastic, 1.5 to one hundred million tons of which will accumulate in landfills, or exposure to nature. The poly (PET) plastic richest terephthalate, global production of nearly 70 million tons per year – it is what we are likely to come into contact with everyday plastic bottles. The plastic bottle recycling, environmental protection play a crucial role. This is the cover story in the latest issue Nature of interest. But now recycling technology, or destroys the mechanical properties of PET, or is too low efficiency of enzymatic hydrolysis. Recently, a team from the University of Toulouse, France put forward a new enzyme: hydrolysis may be 90% of PET plastic bottles in 10 hours. Related articles to \”An engineered PET depolymerase to break down and recycle plastic bottles\” was published in \”Nature\”, the day of \”Science\” magazine \” \’A huge step forward.\’ Mutant enzyme could vastly improve recycling of plastic bottles\” were reported. This efficiency is all PET hydrolase to be higher than before, more importantly, the monomer, and petrochemical materials produced after hydrolysis of the monomer having the same characteristics. This has greatly promoted the repeated re-use plastic bottles.

PET: I want to \”dissolve\” the

in order to hydrolyze PET, to first understand it. PET form can be solidified into two kinds: one is tightly packed crystalline form, and the other is loose, disordered morphology. Most plastic bottle exist two types of PET form, the manufacturer according to the material properties of the plastic bottles, adjust their proportions. But the crystalline form of PET, its structure is too stable, so that the most effective enzyme is difficult to completely digest. You may ask, will not the high temperature crystalline PET form, become loose and disorderly? But the presence of the enzyme \”high temperature intolerant\” ah, a temperature up, the enzyme becomes inactive. How that turned this \”two mountains\”, so that a better enzyme hydrolysis PET? The first is structural problems. Now the researchers cutinase (cutinase, one kind of α / β hydrolase) structure, and the chemical mimetic, identify the location of the interaction of this enzyme with PET: they found that \”recess\” and the PET surface of the enzyme coincides with (including the cut position PET). In order to improve the fit recess and PET, researchers created mutant versions of a large number of enzymes, by different combinations of amino acid changes inside each recess. Next, the enzyme is not heat problem. After the relevant enzymes do the research seems to have a clue: many enzymes by interacting with a metal ion to stabilize the two parts of such metal ions to the enzyme together. Thus, from the start of the original version of this enzyme, researchers in two amino acid engineering may form a chemical bond between the two portions. This version of the enzyme, will be more stable at high temperatures. Finally, the researchers through a series of improvements, creating two versions of the enzyme, and experiments on shredded plastic bottles.

only high efficiency of hydrolysis, very cheap

After the thus modified hydrolase, efficiency is very high. Previous proposed hydrolase, 20 hours half digest PET. In this work, only 15 hours, digestibility can reach 85%. Moreover, by optimizing the conditions, they can be within 10 hours PET decomposition rate of 90%. Although some residual crystalline form of PET, but this is already very high efficiency: can be extracted from 863 kg to 1000 kg of raw material PET scrap. In other words, the efficiency of this enzyme redesign, decomposition amylase efficiency is even higher than our bodies. Then, the researchers also use these raw materials to industry standards for manufacturing a new PET products. The ability to withstand these new products, only lower than the value of PET with standard chemical raw materials to produce 5%; appearance there was only 10%, in line with standard PET production. Of course, cost is also an important consideration. Compared with petrochemical raw materials, use of recycled PET cost is how much? Researchers estimate that if the cost of manufacture of such proteins is 25 US per kilogramElement, then the cost of this process would be the cost of manufacturing a 4% PET by this protein. While this may not be so cheap petrochemical products, but relatively speaking, it is not the future price shocks, but also more sustainable.

One More Thing

The enzyme can not be recycled other major types of plastic, such as polyethylene and polystyrene, is more difficult to break the bond between them. However, if successful, it can help society to solve one of the most challenging problems of plastic we face. Nature thesis: https: //www.nature.com/articles/s41586-020-2149-4 reports: https: //arstechnica.com/science/2020/04/researchers-engineer-enzyme-to-break-down -plastic-bottles /