Reuse plastic waste to trigger radical chain reactions, improving process safety and efficiency

Single-use plastics are a major environmental concern, but now, rather than being thrown out with the trash, used plastic bags from the grocery store could be used to perform a reaction to detoxify dangerous chemicals.

A team led by researchers at the Institute for Chemical Reaction Design and Discovery (WPI-ICReDD) at Hokkaido University has developed a method that uses common plastics instead of potentially explosive compounds to trigger radical reactions in chain.

This approach significantly increases process safety while also providing a way to reuse common plastics such as polyethylene and polyvinyl acetate. These results were published in Journal of the American Chemical Society.

The researchers used a ball mill, a machine that rapidly shakes a steel ball inside a steel pot to mix solid chemicals. When the ball hits the plastic, the mechanical force breaks a chemical bond to form radicals containing a highly reactive unbonded electron. These radicals facilitated a self-sustaining chain reaction that promotes dehalogenation – the replacement of a halogen atom with a hydrogen atom – of organic halides.

“Using commodity plastics as chemical reagents opens up a whole new perspective on organic synthesis,” said Associate Professor Koji Kubota. “I believe this approach will lead not only to the development of safe and highly effective radical reactions, but also to a new way of using plastic waste, which is a serious social problem.”

Reuse of plastic waste was demonstrated by adding plastic shreds from a common grocery bag to the bowl of the ball mill and successfully performing the reaction. The team also showed that their method could be applied to the treatment of highly toxic polyhalogen compounds, which are widely used in industry. Polyethylene was used to initiate a free radical reaction that removes several halogen atoms from a compound commonly used as a flame retardant, thereby reducing its toxicity.

The researchers predict that this method will attract industry attention due to its cost and safety advantages.

“Our new approach using stable, cheap and abundant plastic materials as radical chain reaction initiators has significant potential to foster the development of industrially attractive, safe and highly efficient chemical processes,” commented Professor Hajime Ito.