Waste sulfur put to good use

This research now marks a significant step forward in the development of inverse vulcanized polymers. It makes inverse vulcanization more widely applicable, efficient, eco-friendly and productive than the previous routes.”Tom Hasell

A team from the University of Liverpool has demonstrated a new process for developing polymers from sulfur that could lead to a greater use of the waste sulfur produced by the crude oil and gas refining industries. These new polymers could have unprecedented properties different from that of carbon, opening up possible applications for thermal imaging lenses, batteries, water purification and in human health.

Synthetic polymers are one of the most extensively manufactured materials, and there is an increasing need to develop new polymers that are friendlier to the environment. Although sulfur, a by-product of petroleum, is seen as a potential alternative to carbon in the production of polymers, it is not able to form a stable polymer on its own. However, in a process known as “inverse vulcanization” involving high temperatures and long reaction times, it reacts with organic crosslinker molecules to tether the sulfur polymers together so they are more stable and prevent them from decomposing.

As reported in Nature Communications [Wu et al. Nat. Commun. (2019) DOI: 10.1038/s41467-019-08430-8], in exploring ways to improve sulfur polymers to make them more cheaply, more sustainably, or with properties that could lead to new applications, the team discovered a new catalytic process for inverse vulcanization that can reduce reaction times and temperatures, improve reaction yields and the physical properties of the polymers, and also make their synthesis easier and more industrially viable.

The study reports the catalysis of inverse vulcanization reactions effective for a variety of crosslinkers, and reduces the required reaction temperature and reaction time, preventing harmful H2S production, with increased yield and improved properties, and allows the use of crosslinkers that would be otherwise unreactive. As team leader Tom Hasell said “This research now marks a significant step forward in the development of inverse vulcanized polymers. It makes inverse vulcanization more widely applicable, efficient, eco-friendly and productive than the previous routes.”

Although it is usually very difficult to get the crosslinkers to react with the sulfur, by adding a small amount of a catalyst to the reaction they were able to increase the rates of reaction and lower the temperatures. While sulfur polymers have potential applications in thermal imaging, in high capacity batteries that are more stable to repeated charge/discharge cycles, and as filters to remove toxic heavy metals from water, as well as in construction, the team believe there are many other interesting applications yet to be discovered.