Polymer Paint Displays Color To Show Where Damage Hides
Researchers at the University of Illinois have developed a polymer based, damage indicating coating that warns of breaks—from surface paint scratches to internal cracks—on steel and other metallic surfaces.
“Our idea was to put an indicator in small capsules and mix those capsules in the coating,” says Nancy Sottos, professor in the Dept. of Materials Science and Engineering at the University of Illinois Urbana-Champaign. “We’re focused on looking for damage in very thick paints. The motivation was to have the damage trigger the indication.”
If the paint shows a colorful flag where a coating on a pipe or a steel component is dinged before installation, then the coating could be touched up before going into service. That could save a lot of trouble down the road, says Sottos, adding “Sometimes the paint is damaged before the piece arrives. These scratches are often hard to see.”
Little scratches can lead to big problems. Large steel elements, such as pipeline segments or bridge steel, usually are given thick, multilayer coatings. They often
have a primer layer, followed by an epoxy layer, with a polyurethane topcoat for UV protection. Water and other solvents can get into any breach in the top layer
and start corrosion.
“That is called undercutting,” says Sottos. “Water gets underneath, and, if there’s a small scratch, it starts to blister and undercut the coating—and that’s a big corrosion problem.”
Undercutting can reduce the life andstability of the facility, and that’s where Sottos and her team’s damage-indication system shines—or, more accurately, erupts. Any damage to the paint breaks the color capsules that are mixed into it, triggering a localized color change that can be seen with the naked eye.
“There have been a few [unsuccessful] attempts at this in the past,” says Sottos, but she believes her team has found the right encapsulating technique. The first requirement is that the damage indicator must be stable under rain and ultraviolet light—“and that’s a tall order,” Sottos says.
The second requirement is that the capsule be colorless when it goes into the paint. “If you put a bunch of capsules of red dye into the paint, the whole coating
would be red,” she observes. When the indicators are in the capsules, they’re protected. But when a capsule is ruptured by a surface scratch or
rupture in the substrate, the indicator flows out, reacts with amine in the coating and changes to a bright color.
With the technology proven in tests, the next step is commercialization, which is the stage when Sottos’ team will hand it off, she says.
“We’ve started the process of commercialization. There’s a disclosure and commercial patent,and the next step is to have someone license the technology,” she says. Since it has yet to be picked up by a manufacturer, Sottos says she can’t give an exact cost for the system, but as the capsules work well at just under 1% of the total paint by volume, the cost increase may be minimal.
“The raw material costs are very low, and the cost of capsules scales with the amount manufactured,” Sottos says. “It would be a low-cost additive. There’s good economics to it.”
If a manufacturer picks up the technology, the next step is testing for colorstability in tough environments, such as salt fog, she says.