WEB DESK: In the Greek myth of Icarus, wings that melt in the sun are a tragedy. For the U.S. military, however, flying vehicles that vaporize in sunlight could be a potent weapon: picture a drone that vanishes without a trace after covertly delivering supplies to a remote location.
Engineers at the Georgia Institute of Technology have developed a new type of plastic that can form flexible sheets and tough mechanical parts—then disappear in minutes to hours when hit by ultraviolet light or temperatures above 176 degrees Fahrenheit. Previous efforts to make plastics that self-destruct on command have had trouble preventing such materials from disintegrating at room temperature. But the Georgia Tech team’s new substance can remain stable for years, as long as it shuns the sun.
These plastics could also be used to make environmental and medical sensors that dissolve after collecting data or temporary adhesives that come unstuck with the aid of a heat gun. “They are great for applications where you want things to disappear right away,” says Paul Kohl, a chemical and biomolecular engineering professor at Georgia Tech, who presented his team’s latest research on Monday at the American Chemical Society’s national meeting in San Diego.
Kohl’s presentation covered the most recent improvement that Georgia Tech scientists have made to their material, but his team has been working on the formula for years—and it is not the only one trying to craft temporary plastics. The Defense Advanced Research Projects Agency (DARPA) has an entire program—dubbed Inbound, Controlled, Air-Releasable, Unrecoverable Systems, or ICARUS—to fund research that could lead to the development of disappearing air-delivery vehicles, including Georgia Tech’s work.
The task is daunting. Plastic consists of synthetic polymers, long chains of smaller molecules linked with superstrong bonds. Reverting them to their building blocks requires breaking each bond, akin to ripping apart a necklace bead by bead. Because this process can be affected by humidity, acidity, temperature and other factors in a material’s environment, the breakdown can take months—if it happens at all. “There are many synthetic plastics that kind of degrade,” Kohl says, “but it’s a slow and painful process.”
To make durable plastics that quickly destruct on command, Kohl’s team and some other researchers have turned to a molecule called poly(phthalaldehyde) (PPHA). Like all polymers, this one splits up into its building blocks when heated above a certain temperature. But in contrast to the plastics used in bottles and packaging, which only break down at very high heat, PPHA unravels while still below room temperature. This property makes it easy to break down but hard to stabilize.
