The discovery of a new use for waste material left over refining fossil fuels could lead to benefits for the thermal imaging industry.
A University of Arizona-led international team has found that the sulfur left over from the refining process can be transformed into inexpensive, lightweight plastic lenses for infrared detection devices.
“We have for the first time a polymer material that can be used for quality thermal imaging – and that’s a big deal,” senior co-author Jeffrey Pyun, whose lab at the UA developed the plastic, said. “The industry has wanted this for decades.”
The new lenses were created from liquid sulfur and a small amount of an additive combined in a process the researchers named “inverse vulcanization,” after the “vulcanization” process of adding sulfur to rubber to make it more durable. The liquid concoction was poured into a silicone mold similar to those used for baking cupcakes, where it cooled and hardened.
“You can pop the lenses out of the mold once it’s cooled,” Jared Griebel, a UA doctoral candidate in chemistry and biochemistry, said. “Making lenses with this process—it’s two materials and heat. Processing couldn’t be simpler, really.”
The new plastic is transparent to wavelengths of light in the mid-infrared range of 3 to 5 microns, a range ideal for many applications in the aerospace and defense industries, says senior co-author Robert Norwood, a UA professor of optical sciences. In addition, lenses made from the new plastic offer high optical focusing power, meaning they do not need to be very thick to focus on nearby objects.
The new lenses offer a refractive index between 1.865 and 1.745 depending on the amount of sulfur in the plastic. In comparison, most other polymers that have been developed thus far offer refractive indices below 1.6 and transmit much less light in the mid-range infrared, the researchers said in their paper.
The researchers envision the lenses used in a range of applications involving heat detection and infrared light, including handheld cameras for home energy audits, night-vision goggles, surveillance and security systems and thermal imagers used to diagnose heat flow problems in electronics. Other practical applications using the new plastic, such as optical fibers, are also being considered.
