French scientists have found a way to increase the recycling rate of plastics: modification of enzymes can increase the recycling rate of plastic bottles in your hands by 3 times. The relevant research was published in Nature on April 8.

As the most common plastic component in the world, the global annual output of polyethylene terephthalate (PET) can reach 70 million tons. Although many regions list PET plastic bottles as recyclables, the recycling rate is not satisfactory. Only 30% may be recycled and made into low-strength new plastic.

There is another embarrassing problem when recycling: PET plastic has various colors. If it is recycled without distinction, black or gray plastic particles will be produced after high temperature melting. Plastic products of this type are not welcomed by packaging manufacturers. Therefore, these recycled products are often made into carpets or other low-grade plastic fiber products, and the final destination is still landfill or incineration.

In order to solve these problems, researchers searched for enzymes that can decompose PET and other plastic components from various microorganisms. In 2012, researchers at Osaka University in Japan found leaf branch compost cutinase (LLC) in compost. This enzyme can cleave PET molecules, but has the disadvantages of slow decomposition and poor durability.

So, scientists from the University of Toulouse collaborated with the Sustainable Plastics Company to start with the crystal structure of LLC and modify it.

LLC can degrade plastics because it can bond with the chemical bond connecting terephthalate and ethylene glycol in the PET molecule and break it. At the junction, the researchers found a key amino acid, and based on this, hundreds of mutant versions of LLC were transformed. In order to make it work at higher temperatures, the researchers also added thermostable enzymes.

After synthesizing, screening, and comparing a large number of mutant versions, the researchers finally found an enhanced version of LLC, which is 10,000 times more efficient in breaking chemical bonds than the original version. Moreover, the maximum operating temperature of the original version is 65°C, and the enhanced version increases this temperature to 72°C.

In the reactor, the enhanced enzyme can decompose 200 grams of PET plastic within 10 hours, with a decomposition efficiency of 90%. The researchers modified the PET raw materials accordingly and found that the plastic bottles made of the new materials are as strong as those made of traditional plastics.

The technology has expanded its application scale, and related companies are building demonstration plants. It is estimated that hundreds of tons of PET can be recycled each year, and it is planned to be completed next year. However, the technology is currently unable to realize the recycling of other types of plastics such as polyethylene and polystyrene, and it is still unknown whether the technology can be successfully marketed. However, some researchers said that in the future, consumers and manufacturers may be willing to pay slightly higher prices for the same strong but more recyclable recycled plastic.