A UCLA-led team of chemists and engineers has developed a transparent plastic that if fractured will mend itself when heated -- a discovery that can be used to create self-repairing products.
The findings are reported in the March 1 issue of the journal Science.
The material, which the researchers call Automend, is a tough, clear plastic that is solid at room temperature and has mechanical properties similar to epoxy resin. Automend can be fractured and healed multiple times by heating it to 240-250 degrees Fahrenheit (about 120 degrees Celsius).
"If a product constructed with Automend cracks while in use -- such as in a electronic device that heats and cools frequently -- it would repair itself the next time it heats," said Fred Wudl, professor of organic chemistry at UCLA, director of the university's Exotic Materials Institute and principal investigator in the research team.
After healing, the original fracture is invisible, and it retains 60 percent of the plastic's original strength. The material is also transparent to electromagnetic waves, which makes it practical for devices such as the housing for radar or communications equipment.
The UCLA-led research, funded by the Division of Materials Research of the National Science Foundation, has immediate potential use in industrial, military and scientific applications.
"One application for Automend could be for making large lenses, because if cracked the repair would be transparent and would not deform," Wudl said. "Or, it could be used for such applications as the clear domes over aircraft radar that require not only mechanical strength, but also efficient microwave transmission."
Many plastic materials are strong and resistant to breaking. However, once fractured, the broken pieces are cracked irreversibly; even when mended with glue or polymer catalysts, the fractures remain.
"There is a big difference between gluing or melting a plastic to repair it, and self-mending that is possible with Automend," Wudl said. "Conventional methods of repairing plastic join together two broken pieces, but glue or melting does not 'heal' the break. This can be a problem in devices that must be transparent. And, a fracture repaired with glue or by melting retains only about 40 percent of its original strength."
Unlike other self-healing plastics that were developed previously, Automend repairs itself without the addition of a catalyst or other chemicals.
Automend was produced by the UCLA team during experiments using the Diels-Alder reaction to develop extremely hard polymer materials.
"Our original goal was to make a material that approached the hardness of diamonds," Wudl said. "As we worked on this research, we knew the reaction we were using to create the material was also reversible, and that it could have healing properties."
"The resulting polymer -- Automend -- turned out to be not as strong as diamonds, but it is still very strong," Wudl said. "And, Automend features the self-healing property we had also sought."
In addition to Wudl, other researchers on the project include UCLA chemistry graduate students Xiangxu Chen and Kevin Sheran, and post-doctoral fellow Matheus A. Dam; and engineering school faculty Kanji Ono and Ajit Mal; as well as USC graduate student Hongbin Shen and material science professor Steven R. Nutt.