Pearls inspire new material for body armor

BUFFALO, N.Y. — Round, smooth and iridescent, pearls are among the world’s most exquisite jewels; they have fascinated humanity since ancient times, appearing in everything from religious texts to modern art and literature.

Now, these mollusk-grown gems are inspiring a University at Buffalo-led research team in its quest to improve armor.

By mimicking the outer coating of pearls (nacre, or as it’s more commonly known, mother of pearl), researchers created a lightweight plastic that is 14 times stronger than steel and ideal for absorbing the impact of bullets and other projectiles.

The team’s findings appeared in a recent edition of the journal Applied Polymer Materials, published by the American Chemical Society (ACS). It builds upon earlier work featured in The Journal of Physical Chemistry Letters, also published by ACS.

“The material is stiff, strong and tough,” says lead author Shenqiang Ren, PhD, professor in the Department of Mechanical and Aerospace Engineering and a member of UB’s RENEW Institute. “It could be applicable to vests, helmets and other types of body armor, as well as protective armor for ships, helicopters and other vehicles.”

Zhoulei Zhang, PhD, a former member of Ren’s lab who now works at Lawrence Berkeley National Laboratory, is a co-author of the study.

The bulk of the material is a souped-up version of polyethylene (the most common plastic) called ultrahigh molecular weight polyethylene, or UHMWPE, which is used to make products like artificial hips and guitar picks.

When developing the UHMWPE-based material, Ren and Zhang studied mother of pearl, which mollusks create by arranging a form of calcium carbonate into a structure that resembles interlocking bricks. Like mother of pearl, the material has an extremely tough outer shell with a more flexible inner backing that’s capable of deforming and absorbing projectiles.

“Professor Ren’s work designing UHMWPE to dramatically improve impact strength may lead to new generations of lightweight armor that provide both protection and mobility for soldiers. In contrast to steel or ceramic armor, UHMWPE could also be easier to cast or mold into complex shapes, providing versatile protection for soldiers, vehicles, and other Army assets,” said Evan Runnerstrom, PhD, program manager, materials design, Army Research Office.

The work is an advancement of what’s known as soft armor, in which soft yet tightly woven materials create what is essentially a very strong net capable of stopping bullets. KEVLAR is a well-known example.

The UHMWPE-based material Ren and Zhang developed also has high thermal conductivity. This ability to rapidly dissipate heat further helps it to absorb the energy of bullets and other projectiles.

The team further experimented with UHMWPE-based material by adding silica nanoparticles, finding that tiny bits of the chemical could enhance the material’s properties and potentially create stronger armor.

“This work demonstrates that the right materials design approaches have the potential to make big impacts for Army technologies,” Runnerstrom said.

The research was supported by grant funding from the Army Research Office, an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory.