REUSE IT OR LOSE IT

Institutes & Centres

Institute for Nanoscale Science & Technology

Article published on 13 November 2020

Waste can be valuable in ways that we don’t yet realise.
It just takes a visionary to see it.

Associate Professor Justin Chalker looks at waste items through the prism of green chemistry to consider what valuable new materials they can become.

Transformations that he has performed in the Chalker Research Lab at Flinders University have been dramatic: a new class of rubber can be repurposed into incredibly strong building bricks; waste cooking oil becomes an absorbent polymer that can clean oil spills from ocean water. It signals a brave new era of environmentally friendly chemical application.

“This is the ambition of green chemistry, to make materials, molecules and compounds that are useful – and to make sure they are sustainable,” says Associate Professor Chalker, recipient of the Prize for New Innovators in the 2020 Prime Minister's Prizes for Science.

His idea is to establish new, valuable and generally recyclable rubber, plastics and ceramics. Too many materials are used once and then discarded, but Associate Professor Chalker believes functional alternative uses must be investigated by chemists.

“We have to think about how we can recycle them, or repurpose them, or break them down into their fundamental building blocks so they can be used in different ways, to fully inform a circular economy. Right now, we do a pretty poor job of designing materials with the consideration of a full life cycle.”

Many common plastics – polyethylene, polypropylene and polystyrene – are made up of very strong carbon-carbon bonds that limit the ways in which these materials can be recycled. But what if the chemical bonding process was done differently?

Associate Professor Chalker embarked on this new research journey by examining sulphur, an abundant and cheap waste product. “Sulphur is so readily available, with tens of millions of tonnes produced each year as a by-product from petroleum refineries.” However, sulphur is not very soluble, and chemists have a habit of wanting everything they use to be in solution for easy mixing. Tiny proportions of sulphur have long been used in vulcanising techniques to produce rubber, but Associate Professor Chalker tested what happens when much higher proportions of sulphur are used to activate reactions.

He started by combining used canola oil with sulphur to provide an absorbent polymer that has been found to clean up waste mercury (a common toxic by-product of crude gold mining techniques used in third-world countries) and absorb crude oil spillages (ideal for oceanic clean-ups). “One door opens to another. A lot of our research is application driven, and we’ve seized on the unique properties of reactions we’ve discovered to explore their application further.”

Recently, the researchers discovered that a new kind of rubber can be made from waste sulphur, canola oil and dicyclopentadiene from petroleum refining, and can be used together with an amine catalyst to make flexible, repairable, sustainable objects, such as car tyres. This new type of rubber can be seamlessly repaired if damaged and returned to its original strength in minutes, in a low-energy process that can be conducted at room temperature. The new rubber can also be used as a latent adhesive, because the rubber bonds to itself when the amine catalyst is applied to the surface. The adhesion is stronger than many commercial glues and is also resistant to water and corrosion.

Associate Professor Justin Chalker

It’s a significant waste solution breakthrough. At present, about 48 million rubber tyres reach the end of their life in Australia each year, with each passenger car tyre containing approximately 1.5kg of steel and 7kg of rubber, yet only 16% are domestically recycled. Around two-thirds end up in landfill, are stockpiled or illegally dumped.

Regarding the conversion of the new class of rubber to new construction materials, Associate Professor Chalker notes that “what we have come up with is a next-generation building material that could be used to replace concrete, and created with much lower rates of energy consumption”.

Breaking and reforming the bonds of compounds in a radically different way provides a foundation stone for much green chemistry possibility. It results in a whole new class of recyclable, reprocessed materials, and industry is quite eager to engage with the scientists. Three major patents for the new compounds have been sold to international firm Clean Earth Technologies, with one of its staff now working within the Chalker Research Lab to develop their commercial application.

The curiosity within Associate Professor Chalker to find these chemical solutions came from the most unlikely origins. Born in a small Kansas farming community – “located right in the middle of nowhere,” quips Chalker – he earned a scholarship to the University of Pittsburgh, which is famed for its biological science and chemistry programs. Here, he learned how chemical bonds are broken and reformed to make valuable compounds, and it set him on a path to higher studies at Oxford University in England, stimulating grand ideas to be both innovative and creative with chemistry.

“It satisfied both parts of my brain: building something constructive with my hands, and the intellectual satisfaction of solving unanswered questions.”

Recipient of the Prize for New Innovators in the 2020 Prime Minister's Prizes for Science, Associate Professor Chalker is surrounded by like minds in his lab at Flinders University’s Institute for Nanoscale Science and Technology. “It’s an area of great opportunity for young researchers. We make a point of integrating our students early on into our high-impact projects, as a vital part of our mission in education.”