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March 15, 2010

Self-Healing Paint May Keep Vehicles on the Road Longer

nanostruturesA millimeter scratch here or there on a large military transport vehicle doesn’t seem like much to worry about, but over a few months they add up and can expose underlying metal to the elements. For this reason, the U.S. Navy spends billions of dollars each year pulling vehicles and equipment out of service for repainting.

With the goal of reducing these costs, Jason Benkoski and his colleagues in APL’s Milton Eisenhower Research Center are working on a self-healing paint that could extend the amount of time a vehicle remains on the road or equipment remains in service between paintings. With funding from the Office of Naval Research, they’ve developed a primer additive that mimics the self-healing ability of skin by forming a polymer scar across scratches, and also provides protection from rust.

“We wanted to develop a paint additive that you could take off the shelf and add to military-grade primer without having to make any real changes to it,” says Benkoski. “We didn’t want to increase costs, and we didn’t want anyone to need retraining. It’s really a practical approach because we know there’s always a barrier to adopting new technologies. If you can have a technology that gives improved properties without changing anything else, then there’s a higher likelihood of adoption.”

APL Researcher Jason Benkoski

To make the additive, called Polyfibroblast, Benkoski drops tiny spheres of liquid polyurethane into water. “The best analogy for what it looks like is vinaigrette, where you have droplets of oil in a matrix of water,” he says. The water cures (or hardens) the outermost layers of the spheres into a polymer shell. Once the shell forms, it protects the rest of the resin inside, which remains liquid. “The spheres are like microscopic paint cans,” explains Benkoski.

Next, the spheres are coated with nickel and zinc, and the final product is added to primer and painted right onto a steel surface. If the paint gets scratched, the capsules break open and release their store of resin, which flows into the crack and cures as it interacts with moisture in the air. The resin physically protects the underlying metal from moisture, and the zinc serves as a sacrificial surface: it rusts so that the steel underneath does not.

Benkoski says the team developed several unique processes to avoid using any harsh chemical conditions. This not only makes the technology more environmentally friendly and easier on the people producing it but also helps reduce costs.

Lance Baird is compiling data from the Polyfibroblast project to write an article about the development and performance of the additive, supported by a Stuart S. Janney Fellowship. The fellowships provide part-time, short-term opportunities for members of APL’s Professional Staff to undertake endeavors that are not in direct support of sponsored work.

The dry primer has excellent adhesion and wear resistance and has a demonstrated ability to self-heal and provide protection from rust to an underlying metal. Now Benkoski would like to see if it maintains these properties when produced in larger batches. For research purposes, he has produced 20 grams at a time. He’s working with his sponsor to find a partner company that could begin producing and commercializing the additive.