A polymer that self-decomposes when exposed to the sun

Researchers from the Georgia Institute of Technology in Atlanta have succeeded in developing a polymeric system capable of instantly disappearing upon exposure to the sun following self-initiated depolymerization

[Translation by Dr. Nachmani Moshe]

The research team based its decomposition system on cyclic polyaldehydes, such as phthalaldehyde. Breaking just one of the thousands of chemical bonds that make up these ring polymers will lead to immediate disintegration into the monomers that make up the polymer, explains the lead researcher. "The material undergoes immediate depolymerization in one step," adds the researcher.

The problem is the stability of these materials, notes the lead researcher. "Normal polymers are stable at room temperature, but our polymers (polyaldehydes) must be obtained at very low temperatures because they are fundamentally unstable at room temperature," he explains. At the same time, by preparing the polymers at a very high level of purity, the research team was able to make them stable at room temperature. In the next step, the researchers developed additives capable of initiating the self-decomposition. The trigger is a photocatalyst that responds to wavelengths in the visible or ultraviolet range and initiates the bond breaking step leading to the depolymerization of the material as a whole.

The team was able to demonstrate that this depolymerization step can be controlled remotely by turning on a tiny LED located in a device made of the polymer. "The LED is so tiny that it simply collapses when the material breaks down," says the researcher. Even heating the polymer to a temperature of eighty degrees Celsius can initiate the decomposition process. "If you have a battery and a small heating device, you just heat it up a little and it completely disintegrates," explains the researcher. The depolymerization and evaporation process can last from a few seconds to a few hours, depending on the method used and the time of day the device is activated. The research group was also able to figure out how to trigger this self-destruction process with a time delay, so that the device would be stable for a predetermined number of hours.

The material was used to make small detectors consisting of a printed circuit board made of polyaldehydes with silver and copper nanoparticles as the electrically conductive connectors. When exposed to light, the polymer's connectors break down and the printed circuit board disappears. The team also used the material to demonstrate its use in making a parachute that could drop a load hundreds of kilometers and more, and at the point of descent it simply disintegrates and disappears. The researchers also tried to make larger devices. Last year, the researchers placed a five-kilogram parachute inside a helium balloon at night, flew it 70 kilometers and dropped it a short distance from the intended destination, the researcher notes. "The sun hurt the sky and the sun just disappeared," explains the researcher.

Along with its obvious military applications, the material has many civilian uses, the researcher says. For example, temporary protective coatings that wrap consumer products, or environmental detectors designed to monitor the soil content in large fields. "You can scatter detectors in the field, collect the data from them, and then initiate their disappearance at the end of the monitoring," suggests the researcher. "They will simply break down into relatively natural substances that are not toxic to humans or the soil." The researcher points out that concerns regarding exposure to aldehydes and these additives must be addressed before and after their decomposition. "There is no component in the material that is a known harmful substance, however, all the components are chemicals and their product safety leaflet should be referred to before using them," adds the researcher. "This material must be handled with care, and it is not inert like normal plastic, so we must be careful in the use we make of it."

The news about the research on the website of the American Chemical Society