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Self-repairing plastics aim to fix themselves repeatedly

New plastics turn red when damaged, then heal themselves when exposed to light.

 

 

A new genre of plastics that mimic the human skin's ability to heal scratches and cuts offers the promise of endowing cell phones, laptops, cars, and other products with self-repairing surfaces, scientists reported recently. The team's lead researcher described the plastics, which change color to warn of wounds and heal themselves when exposed to light, at the 243rd National Meeting & Exposition of the American Chemical Society (ACS), the world's largest scientific society.

"Mother Nature has endowed all kinds of biological systems with the ability to repair themselves," explained Professor Marek W. Urban, Ph.D., who reported on the research. "Some we can see, like the skin healing and new bark forming in cuts on a tree trunk. Some are invisible, but help keep us alive and healthy, like the self-repair system that DNA uses to fix genetic damage to genes. Our new plastic tries to mimic nature, issuing a red signal when damaged and then renewing itself when exposed to visible light, temperature, or pH changes."

Urban, who is with the University of Southern Mississippi in Hattiesburg, foresees a wide range of potential applications for plastic with warn-and-self-repair capabilities. Scratches in automobile fenders, for instance, might be repaired by simply exposing the fender to intense light. Critical structural parts in aircraft might warn of damage by turning red along cracks so that engineers could decide whether to shine the light and heal the damage or undertake a complete replacement of the component. And there could be a range of applications in battlefield weapons systems.

Plastics have become so common, replacing steel, aluminum, glass, paper, and other traditional materials, because they combine desirable properties such as strength, light weight, and corrosion resistance. Hundreds of scientists around the world have been working, however, to remedy one of the downsides of these ubiquitous materials: Once many plastics get scratched or cracked, repairs can be difficult or impossible.

Self-healing plastics have become a sort of holy grail of materials science. One approach to that goal involves seeding plastics with capsules that break open when cracked or scratched and release repairing compounds that heal scratches or cuts. Another is to make plastics that respond to an outside stimulus – like light, heat, or a chemical agent – by repairing themselves.

Urban's group developed plastics with small molecular links or "bridges" that span the long chains of chemicals that compose plastic. When plastic is scratched or cracked, these links break and change shape. Urban tweaked them so that changes in shape produce a visible color change – a red splotch that forms around the defect. In the presence of ordinary sunlight or visible light from a light bulb, pH changes, or temperature, the bridges reform, healing the damage and erasing the red mark.

Urban cited other advantages of the new plastic. Unlike self-healing plastics that rely on embedded healing compounds that can self-repair only once, this plastic can heal itself over and over again. The material also is more environmentally friendly than many other plastics, with the process for producing the plastic being water based, rather than relying on potentially toxic ingredients. Now is working on incorporating the technology into plastics that can withstand high temperatures.

Urban acknowledged research funding from the U.S. Department of Defense.

Source: The American Chemical Society

Published April 2012

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