With a zap of electricity, recyclable (and recycling) polymers can form

A little electricity has helped a team of chemists to make sustainable polymers that could improve e-waste recycling, precious metal mining and perhaps even work as antimicrobials.

The team, from Flinders University, has tapped into the concept of ‘electrochemistry’ to develop a simple and quick reaction to make their polymers.

The reaction can be done at room temperature, with no additional ingredients – meaning it doesn’t need extra energy or hazardous chemicals.

They’ve published their method in the Journal of the American Chemical Society.

The reaction begins with a low-cost substance called a “trisulphide”: an organic (carbon-containing) molecule with three sulphur atoms in it.

When an electron is added via electricity, the sulphur atoms in one molecule bind to sulphur atoms in another, setting up a systematic chain reaction.

This forms a polytrisulphide: a long molecule made up of repeating units, linked together with sulphur atoms.

This sulphur polymer can bind to precious metals, like gold. The researchers tested it out on mixtures that resembled ones produced in gold mining and e-waste recycling, and found it could remove 97% of the gold.

Diagram of reaction
The fully recyclable process: electricity makes the polymer, the polymer recovers gold and is turned back into monomers with heat, then electrified back into a polymer. Credit: Chalker lab

“The use of electricity to produce new materials is an emerging field of research that opens many doors to new chemicals and polymers that can be produced in a more sustainable way,” says co-author Dr Thomas Nicholls.

Co-author Professor Justin Chalker says that while electrochemistry has been used for a while in metal refining, battery technologies, future fuels like hydrogen, and making disinfectants like chlorine, using it to make complex molecules like this polymer is a relatively new field.

“The interest is growing because only electricity is needed to provoke the key reactions, and they can be tuned to react selectively at different parts of the molecules. In our case, this selectivity allowed a unique way to make a recyclable polymer,” says Chalker.

The polymer is recyclable because it can easily be converted back into its single-molecule building blocks, ready to use again.

“Our method to electrochemically produce polymers provides new materials that are highly functional and environmentally friendly,” says first author Jasmine Pople, a PhD candidate at Flinders.

Pople adds that the method “may generate less waste than traditional chemical syntheses, and it can be powered with renewable energy”.

Two people smiling in lab
Green chemistry researchers Dr Thomas Nicholls and Jasmine Pople. Credit: Flinders University

With some quantum mechanical calculations, the team was able to figure out exactly how their polymer grew.

“The polymerisation has a clever self-correcting mechanism: whenever the wrong reaction occurs, it reverses until the correct reaction proceeds, ensuring a uniform polymer,” says co-author Dr Le Nhan Pham.

Next, the team is planning to see what other polymers they can make with this technique.

“There are a variety of new structures and functions we want to build into these polymers,” says Chalker.

“We also have plans to broaden the length of the polymer chains to improve their mechanical properties.

“With new functional groups, we envision applications in biochemistry, sustainable construction, battery technologies, smart coatings and more.”

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