Japanese researchers develop novel radical chain reaction method to recycle and detoxify plastic waste

08 Jan 2024 --- Researchers at the Institute for Chemical Reaction Design and Discovery, Hokkaido University, Japan, have unveiled a novel method that employs common plastic materials to initiate radical chain reactions, which offers a way to detoxify and recycle plastic waste.

Published in the Journal of the American Chemical Society, the researchers detail a method that utilizes everyday plastics such as PE and polyvinyl acetate to kickstart radical chain reactions. These reactions, facilitated by a ball mill — a machine that rapidly shakes a steel ball inside a steel jar — detoxify hazardous chemicals commonly found in industrial processes.

“The use of commodity plastics as chemical reagents is a completely new perspective on organic synthesis,” says associate professor Koji Kubota. “I believe that this approach will lead to not only the development of safe and highly efficient radical-based reactions but also to a new way to utilize waste plastics, which is a serious social problem.”

The researchers demonstrated the efficacy of their method by adding plastic shreds from a common grocery bag to the ball mill jar and initiating the reaction. 

“When the ball slams into the plastic, the mechanical force breaks a chemical bond to form radicals, which have a highly reactive, unbonded electron. These radicals facilitated a self-sustaining chain reaction that promotes dehalogenation — that is, the replacement of a halogen atom with a hydrogen atom — of organic halides,” explain the authors.

According to the researchers, this approach showcases the potential for recycling plastic waste, particularly single-use plastic bags, to detoxify hazardous chemicals, transforming them from environmental hazards to valuable resources.

The team illustrated the versatility of their technique by applying it to the treatment of highly toxic polyhalogenated compounds commonly used in various industries. Using PE as an initiator, the researchers successfully initiated a radical reaction that removed multiple halogen atoms from a flame retardant compound, thereby reducing its toxicity.Shreds of a grocery bag were utilized to initiate a reaction in a ball mill jar (Image credit: Koji Kubota, et al. Journal of the American Chemical Society).

“Cost-effective and safe”
The recycling technique seeks to address the plastic waste crisis. It reportedly provides a safer and more efficient method for treating hazardous chemicals in various industries, “marking a step toward a more sustainable and environmentally conscious future.” 

“We postulated that mechanical activation of thermodynamically stable covalent bonds could develop a more convenient and safer alternative for radical chain initiation. Here, we show that commodity plastics such as PE and poly(vinyl acetate) can act as efficient initiators for radical chain reactions under solvent-free mechanochemical conditions,” write the researchers.

“In this approach, polymeric mechanoradicals, which are generated by homolytic cleavage of the polymer chains in response to the applied mechanical energy provided by ball milling, react with tris(trimethylsilyl)silane to initiate radical chain dehalogenation of organic halides. Preliminary calculations support our proposed force-induced radical chain mechanism.”

The researchers anticipate their method will attract widespread attention from industries seeking cost-effective and safe chemical processes.

“Our new approach using stable, cheap and abundant plastic materials as initiators for radical chain reactions holds the significant potential to foster the development of industrially attractive, safe and highly efficient chemical processes,” comments professor Hajime Ito.

Edited by Radhika Sikaria