Whenever eyes are glued to the latest release of a sparkly new feature-heavy gadget, much less thought is given to the fate of our old, soon-to-be-replaced electronic devices. Unfortunately, the vast majority of Singapore’s electronic waste (or e-waste) is destined for the landfill, where their slowly degrading plastic components wreak environmental havoc.
“In Singapore, about 60,000 tons of e-waste are produced every year—but only a mere 6 percent is recycled,” said Jie Zheng, a Research Scientist at A*STAR’s Institute of Sustainability for Chemicals, Energy and Environment (ISCE2).
Zheng says plastic components within electronics’ inner workings are to blame for this troubling statistic. “Metal components in electronics are typically bound to strong, durable and chemically resistant plastics called thermosets, which makes them extremely difficult to separate for recycling.”
Swapping out these ’bad’ plastics for more sustainable alternatives could move e-waste out of landfills and back onto production lines. With this in mind, Zheng led a collaborative endeavour with researchers from the National University of Singapore (NUS) and Nanyang Technological University (NTU) to focus on finding greener plastics for use in one of the most common applications for thermosets—thermoelectric generators (TEGs).
TEGs scavenge heat to generate electricity and have protruding metal structures, called ‘legs’, that bridge the electrical flow between components. Traditionally, legs are insulated by thermosets which are difficult to strip from the underlying metal, making recycling highly inefficient.
Zheng and colleagues saw a solution in a different class of plastics called vitrimers. These polymers are not only easy-to-recycle, but also remarkably strong and flexible, so as not to compromise on functionality when replacing thermosets.
“Vitrimers owe their flexibility to their inherent chemical structure, which contains dynamic covalent polymer networks (DCPNs),” explained Zheng. “Such networks can be decomposed on demand when subjected to an external stimulus such as heat or the presence of chemicals; they’re living, reprogrammable and self-healing.”
Vitrimers are networks of crosslinked plastic polymers. These links (covalent bonds) are dynamically associated, allowing them to be reversibly broken and reformed under heat, light, chemicals or other external stimuli.
© A*STAR Research
To test their theory, the researchers simulated e-waste recycling by submerging vitrimer-encapsulated TEGs into warm solvents. As anticipated, the plastic coating on the component’s legs melted away with ease, revealing electrical components that can be further reprocessed and reused. Next, the researchers used the recycled components to build a new TEG from scratch, which excitingly, performed as well as its parent device, further validating the reliability of their technique.
Zheng said these results demonstrate how vitrimers could spark a circular economy in the electronics industry. Recyclable thermoelectric devices are just the start—vitrimers could also be used in everything from cooling components to powering electronic screens.
Moving forwards, Zheng plans to grow the green polymer toolkit further, with more diverse options for sustainable electronics. “For instance, some materials containing light-sensitive polymer networks can be degraded by simply exposing them to light, which initiates the recycling process,” said Zheng.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Sustainability for Chemicals, Energy and Environment (ISCE2) and the Institute of Materials Research and Engineering (IMRE).
