Researchers at University of North Carolina at Chapel Hill in the US have demonstrated a new approach to recycling plastic through modifying its carbon–hydrogen bonds, one of the strongest chemical bonds in nature. The breakthrough, which involves transforming plastic into a material that is both tougher and stronger, could help to substantially reduce the amount of waste that goes to landfill.
The current rate of recycling in most countries remains very low because of the chemistry of the plastic manufactured in huge volumes by industry. The US, for instance, produces around 46.3 million tons of plastic waste every year, only 9% of which is recycled. This is partly due to the stability of the carbon–hydrogen bonds ubiquitous in plastics and medicines, which make the material difficult to recycle. Even most recycled plastic goes into lower quality products such as polyester clothing and eventually ends up in landfills.
However, as reported in the journal Science [Fazekas et al. Science (2022) DOI: 10.1126/science.abh4308], the team of chemists developed a method to break down plastics to create a new material that is stronger and tougher than the original, which means it is also potentially more valuable. After developing a super-absorbent polymer capable of extracting dangerous chemicals from drinking water, the same technique was used to transform difficult-to-recycle plastic waste into a valuable class of polymers using the plastic foam packaging that protects electronics when being shipped, which would normally just be thrown out.
This foam is made of a low-density plastic called commercial polyolefin, and by selectively pulling hydrogen atoms from polyolefin they were able to expand the life of the single-use plastic into a plastic known as an ionomer, currently used in a range of food packaging. By altering these carbon-hydrogen bonds, the life span of the polymers could be extended beyond single-use. As researcher Frank Leibfarth points out, “Our approach views plastic waste as a potentially valuable resource for the production of new molecules and materials. We hope this method could drive an economic incentive to recycle plastic, literally turning trash into treasure.”
A newly identified reagent was used that can remove hydrogen atoms from medicinal compounds and polymers without immediately trapping the carbon, making new bonds in places that were previously thought unreactive. As researcher Erik Alexanian said, “The versatility of our approach is that it enables many valuable transformations of carbon–hydrogen bonds on such a wide range of important compounds”.
“The versatility of our approach is that it enables many valuable transformations of carbon–hydrogen bonds on such a wide range of important compounds”Erik Alexanian