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New process makes “biodegradable” plastics easier to decompose

Biodegradable plastics have always been considered to help solve the problem of plastic pollution, but today most of the “compostable” plastic bags are mainly made of polylactic acid (PLA), which is not decomposed during the composting process and can also pollute other recyclable plastics. However, the latest research published on the 21st in the journal Nature claims that American scientists have invented a new process: using only heat and water, these compostable plastics can be decomposed more easily.

Previously, Xu Ting, professor of materials science and engineering at the University of California, Berkeley, and his research team discovered an enzyme that can degrade toxic organophosphorus chemicals and designed a molecule called random heteropolymer or RHP. These The molecule envelops the enzyme, which can be gently combined without restricting the natural toughness of the enzyme to protect the enzyme from disintegration. RHP is composed of 4 types of monomer subunits, each of which has the chemical property of interacting with chemical groups on the surface of a specific enzyme. They degrade under ultraviolet light and are present in a concentration of less than 1% of the weight of the plastic.

In this study, the research team used a similar technology. When making plastic, they wrapped billions of nano-scale edible polyester enzymes in RHP and embedded them in plastic resin beads.

Research found that RHP-encapsulated enzymes will not change the properties of plastics. When exposed to heat and water, this enzyme will get rid of the polymer coating material and break down the plastic polymer. Plastic can be melted at a temperature of about 170 degrees Celsius and extruded like ordinary polyester plastic fibers. In the case of PLA, enzymes will reduce it to lactic acid, which can “feed” the soil microorganisms in the compost. The polymer wrapping material will also degrade.

“For PLA, the researchers used an enzyme called proteinase K, which can chew PLA into lactic acid molecules; for polycaprolactone (PCL), they used lipase. These two enzymes are cheap and easy to obtain.

To cause plastic degradation, only water and a small amount of heat are required. At room temperature, 80% of the modified PLA fiber is completely degraded within a week. The higher the temperature, the faster the degradation rate. Under industrial composting conditions, modified polylactic acid degrades within 6 days at 50 degrees Celsius. PCL, another polyester plastic, degrades within two days under industrial composting conditions at 40 degrees Celsius.

Up to 98% of the plastics made by this process will be degraded into small molecules. And this process avoids the production of microplastics.

Researchers said that modified polyester will not degrade at lower temperatures or short-term humidity. It can be degraded when immersed in warm water, which means that plastic can be composted at home.

Post time: Apr-27-2021