“Yellow Chemistry”: Waste Sulfur Turned into New Plastic

University of Arizona scientists have invented a new plastic they say is ideal for lenses in infrared devices like heat-sensing cameras.

A small group of scientists at the University of Arizona (UA) have been working on “yellow chemistry”, which like the “green chemistry” pursuits of others, promises to benefit the environment but also deliver a new class of inexpensive plastics. “Yellow” here because the material is based on sulfur. The material has properties that makes it ideally suited for use in lenses in infrared devices like heat-sensing cameras. The new hybrid material is called CHIPs—Chalcogenide Hybrid Inorganic-Organic Polymers.

The invention is the result of cross-campus collaboration including lead scientist Jeffrey Pyun, professor in the UA’s Dept. of Chemistry and Biochemistry; UA optical sciences professor Robert Norwood; and UA chemistry and biochemistry professor Richard Glass. Pyyn discovered the new type of plastic as part of the research on sulfur-based materials for advanced batteries, which started back in 2010. At that time, Pyun and his colleagues were focused on using waste sulfur from the petroleum refining industry as a low-cost feedstock for a new kind of plastic.

Sulfur you can get for the same magnitude of cost of coal, so it’s literally dirt cheap

Aside from its use as a semiconductor in batteries, the team found that the new material has a very high “refractive index”—a measure of how light bends as it passes through a material. High refractive index materials allow opticians to make thinner eyeglass lenses and also help lenses on infrared devices “see” more infrared radiation. Pyun noted that lens materials for infrared imaging are typically made of germanium and chalcogenide glass, which contains elements that create a high refractive index but can be complex and costly to produce. In contrast, sulfur is cheap and abundant as a refining byproduct and is very simple to turn into plastics. “Sulfur you can get for the same magnitude of cost of coal, so it’s literally dirt cheap,” he has said.

With the help of Tech Launch Arizona and Paul Eynott, TLA licensing manager for the College of Science, Pyun and his team are starting to court industrial partners that could license the technology and start incorporating it into products. Pyun also has formed a startup company, Innovative Energetics, to further develop commercial technologies, as it’s believed that the sulfur-based plastics could be used for a myriad of applications.

In the meantime, though, the emphasis is on infrared optics, for which a big market is likely to emerge for use in lenses for industrial infrared applications ranging from missile target seekers and night-vision equipment to the infrared detectors used in self-driving vehicles.  Moreover, the material could be used with smartphones to create heat-sensing apps, such as an app that could detect the higher heat signature of ripe fruit vs. an unripe one. Pyun has said that this is very exciting as it’s a first and his team has uncovered an “enormous new world for plastics in this already established area”.