The French biotech start-up company called 'Carbios' succeeded in developing an enzymatic process to recycle the plastic polyethylene terephthalate (Polyethylene terephthalate) back to its component monomers, from which the finished polymer can be produced again
[Translation by Dr. Moshe Nachmani]
"Everyone believes that polyethylene terephthalate can be easily recycled in light of the fact that plastic bottles made of it can be easily recycled mechanically," says the company's CEO Emmanuel Ladent. "However, plastic food trays are not recyclable; Most of the packaging products for cosmetics are not recyclable; Most polyester fibers, which are also composed of polyethylene terephthalate, are not recyclable; Therefore, most of the amount of polyethylene terephthalate waste today cannot be easily recycled."
Instead of competing with mechanical recycling processes, such as those used for plastic bottles, the company focuses on more complex processes. "Recycling of polyester fibers is a large market in itself. Two-thirds of the total amount of polyethylene terephthalate is actually polyester fibers," explains the CEO.
The company's chief scientist explains that the need to find an enzyme capable of breaking the ester bonds between the polymer chains was initially particularly daunting. "I knew many of my colleagues who worked in the field of cellulose. Decomposing the cellulose compound was a real scientific nightmare, and at first I thought that decomposing polyethylene terephthalate with the help of an enzyme would surely be challenging and difficult." The research team began its experiments with an enzyme described by a research group from Japan in 2012, which was developed to break down the waxy material cutin that covers the leaves of plants. This enzyme is able to break down small amounts of polyethylene terephthalate, but a large amount of enzymes is required for this and the process itself lasts several weeks. Through a process of 'directed evolution', the research team developed improved enzymes that work faster, and are resistant to higher temperatures than usual. "We literally redesigned the active site in the enzyme."
The material polyethylene terephthalate can be crystalline or in an amorphous configuration, explains the main researcher; However, the enzymatic degradation is much more efficient when the configuration is amorphous, and therefore the researchers had to develop a pre-treatment step to ensure that the material inside the backing remains in its amorphous configuration. "We were able to produce elongated pellets of amorphous polyethylene terephthalate with a high surface area in favor of extensive contact between the polymer and the enzymes," explains the researcher. Increasing the thermal stability of the enzyme helps to speed up the rate of the discharge reaction, but also to keep the reaction close to the glass transition temperature of polyethylene terephthalate, which is seventy degrees Celsius. "This fact allows us to take advantage of the fact that the polymer chains are more mobile," says the researcher. However, polyethylene terephthalate may undergo recrystallization at temperatures close to this, so the reaction conditions must be carefully controlled in order to minimize as much as possible the formation of competing processes. At the end of the reaction, the liquid monomers terephthalic acid as well as ethylene glycol can be separated and purified, then they can be sent directly to the re-production of the polymer. "Almost all global production of polyethylene terephthalate uses these monomers," says the researcher. This means that it will be easy to attach a recycling plant directly to existing polyethylene terephthalate production plants. In view of the fact that the developed enzymes are selective for the release of polyethylene terephthalate only, any small amount of other polymers present in the original mixture, such as polyamides or polyolefins, as well as any presence of dyes or additives, can be easily filtered out. "This means that we don't need to use oppressive sorting processes in the initial stage - the enzymes will do it themselves," says the CEO.
Production licenses for many companies to quickly influence the extent of fossil fuel use
"The company's first factory should be built with the company's own investment," said the CEO, but beyond that, the company intends to give production licenses for its technology to trade partners all over the world. "If we want to reduce as much as possible the carbon footprint and water consumption in the world, it will be necessary to build local factories for the treatment of waste water, as well as to create the monomers that are reused again and again within the framework of the local industry", he adds and says. This is also a question for Katsav: "If we are interested in spreading our technology with the help of our own capital, through our fundraising, it will take decades. We don't have that time in the current state of the earth - we must act quickly!"
Regulatory provisions as well as the vision of consumer brand corporations are also pushing towards greater amounts of recycling. The European Union has an ambitious goal of achieving a level of thirty percent recycling of all plastic packaging by the year 2030, and even this goal should increase at a fairly rapid pace after 2030. "This type of arrangement is also starting to appear in some countries in the US and Asia," notes the CEO . "And perhaps more importantly, many consumer brand corporations express commitments to comply with even stricter regulations, in terms of the required recycling percentages and the development of more efficient ways to treat wastewater. So the industry itself is vigorously urging to move forward quickly and recycle more and more products."
The enzymes of the start-up company break down the polyethylene terephthalate plastic into its monomers: terephthalic acid as well as ethylene glycol, which themselves can be used directly in existing plants to re-produce the polymer
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