Material Is Self-Healing
Source: NewsMax.com
February 15, 2001
WASHINGTON (UPI) - Researchers have developed a new
material they say is capable of healing itself in much the same
fashion as a biological organism. The discovery could one day lead to
longer-lasting and structurally self-repairing planes, bridges,
buildings and prosthetic devices, they will report today in the journal Nature.
Researchers at the University of Illinois have created a
composite material containing densely packed capsules. Each is filled
with a chemical agent that automatically heals the surrounding
material when released.
"We were essentially trying to mimic what the human body
does quite naturally," said Scott White, an Illinois chemical engineer
and lead author of the paper.
"The body self-assembles, puts itself together in
prescribed architecture, and the process is driven naturally. In one
small sense, we've achieved that."
Composites are solid materials made of substances with
different physical characteristics. Ideally, such a blend of
ingredients would each original characteristic, such as rigidity or
malleability, while contributing desirable properties to the whole.
Nowadays composites are ubiquitous, appearing in
airplanes, sporting equipment, microelectronics and even some types of
dinnerware. Yet despite their unique properties, composites often
crack if exposed to enough heat or pressure.
"Once a material like fiberglass cracks, the integrity
of its structure is compromised," White told United Press
International. "But in this material, repairs begin as soon as cracks
appear."
Tests show the repaired material capable of regaining
about 75 percent of its original strength, he added.
White noted Boeing and Motorola are interested in
working with the composite. Circuit boards in electronic devices often
crack, interfering with electrical processes. And aircraft made from
the composite would theoretically last longer and boost safety.
The capsules can be thought of as tiny microballoons
about 100 microns, or 100 millionths of a meter, in diameter, said
Richard Wood, a chemical engineer at the University of Delaware. Wood
reviewed the paper for Nature.
The capsules are filled with polymer monomers, a basic
building block from which the composite material itself is made. When
the composite degrades, cracks in the material rupture the tiny
balloons, releasing the healing polymers. They then mix with special
catalysts sprinkled throughout the
material before binding to and repairing the fractured areas.
The researchers said the main design obstacle was
finding the right size and thickness for the microballoons. The task
was to develop a shell thick enough to withstand heat and agitation
during manufacturing but thin enough for a crack to rupture it - the
most difficult part of the work, said White.
Self-repairing composites are a grail for material
engineers. Since the 1950s the need for light, highly rigid materials
to make airplanes, space craft, weapons, sporting equipment and
electronics have driven researchers to find newer and better
combinations of materials. Civil engineers, for example, want
self-repairing composites to build a myriad of structures from bridge
parts to roof coatings.
Experts said the discovery was exciting but likely would
not appear in everyday products for some time.
"For one thing we have to wait and see if it is
economically feasible to produce the material on a mass scale," said
Philippe Geubelle, another Illinois researcher on the project. "That
is one thing we haven't talked much about."
Other experts questioned whether the microballoons would
make the material heavier, which could offset its healing qualities
especially in aerospace and biomedical applications.
But White told UPI the microballoons weighed less than
the composite itself, making the material lighter than normal.
White's team worked on the project for six years,
starting in 1995 with a seed grant from the Army Corp of Engineers.
The University of Illinois and the U.S. Air Force, which did not offer
comment for this story, provide funding.
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