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Sci Tech
Self-repairing plastic
A 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 by the university of California-Los Angeles (ULCA) are reported in 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. It can be fractured and healed multiple times by heating it to 240-250 degrees Fahrenheit (about 120 degrees Celsius).
"If a product constructed with the material cracks while in use — such as in an 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 per cent of the plastic's original strength. The material is also transparent to electromagnetic waves, which makes it practical for devices such as 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 it 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," 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 per cent 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.
It was produced by the team using the Diels-Alder reaction to develop extremely hard polymer materials, says the report from Science.
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