Plastics are both a commodity and a problem. They have simplified human life significantly, but they are an environmental nuisance. There are two methods currently employed to reduce plastic waste every year: recycling petroleum-based plastic or using biodegradable plastic made from organic materials. There is now a new approach that combines the two.
Chemists from Colorado State University have developed a bioplastic that can be perfectly recycled. The plastic can be turned back into its fundamental component simply by heating it up to 220°C (430°F), or slightly higher for the more complex configuration of the molecules. This is the first recyclable biodegradable plastic and the findings are published in Nature Chemistry.
Plastics are made by long molecules called polymers. These polymers are chains of repeating units, usually a single simple molecule (a monomer), linked together through a chemical process. Depending on the nature of the process, you can create different polymers: The chemical elements in a plastic bag and a plastic bottle might be the same, but they are arranged in a different way so they have different properties.
"More than 200 pounds [90 kilograms] of synthetic polymers are consumed per person each year – plastics probably the most in terms of production volume. And most of these polymers are not biorenewable," Eugene Chen, coauthor of the study, said in a statement.
"The big drive now is to produce biorenewable and biodegradable polymers or plastics. That is, however, only one part of the solution, as biodegradable polymers are not necessarily recyclable, in terms of feedstock recycling."
The new polymer is not only recyclable, it also doesn't need oil for its production. The monomer used to produce the new plastic is called Gamma-butyrolactone, or GBL, a common colorless liquid that can be easily extracted from biomass. A polymer has been produced from GBL in the past but under extremely difficult conditions (a temperature of 160°C/320°F and a pressure of 20,000 atm) and the molecule was thus declared non-polymerizable.
The scientists found a way around this apparently insurmountable problem: they used a catalyst and reduced the temperature, and were able to create linear and cyclic polymers. "In my 15 years at CSU, I would probably call this my group's most exciting piece of work," Chen said. "This work creates a class of truly sustainable biopolymers, as they are both biorenewable and recyclable, based on a bioderived monomer previously declared non-polymerizable."