Patented Technique Makes For Tougher Heat-Resistant Plastics

Scientists here have patented a method of mixing plastic with silica to create a material three to four times tougher than the plastic alone.

Plastic engine parts would mean lighter, more fuel-efficient cars and airplanes, but today's heat-resistant plastics aren't tough enough -- they shatter at the smallest impact, said John Lannutti, associate professor of materials science and engineering at Ohio State.

The new composite material is tougher than plastic alone because it divides the force of an impact into many small interactions involving millions of individual silica particles.

"We think that as a crack starts traveling through the composite, it breaks up into finer and finer cracks, until the material has dissipated the energy of the impact," Lannutti said.

Lannutti developed the method of producing these materials with Robert Seghi, associate professor of restorative and prosthetic dentistry at Ohio State, and graduate student Jiazhong Luo. Their goal, at first, was to create tough plastic dental fillings.

After moderate success -- they created a plastic that was about as good as today's standard fillings -- Lannutti tried the technique with a different kind of plastic for Ohio Aerospace Institute member BFGoodrich Co.

BFGoodrich supplied plastic powder for Lannutti's experiments, and will manufacture parts containing this silica for further testing.

annutti and his colleagues call the method "synergistic toughening," or "toughening across scales," because it strengthens material down to the scale of the individual particles.

The silica particles they use are only 50 nanometers wide -- about 100 times smaller than the width of a human hair -- and each particle contains a host of even smaller pores that measure only a couple of nanometers across.

What makes the patented manufacturing method unique is that the researchers force melted plastic to fill these tiny pores, creating a strong bond between atoms of silica and plastic over a large surface area.

"So basically we can create toughness that starts at the nanoscale," said Lannutti.

Eventually consumers may one day find more plastic parts under their car hoods, or on a commercial airplane wing -- places where iron, steel, and aluminum are used today, Lannutti said. Sooner than that, though, military aircraft will probably take advantage of the technology.

It was military testing of parts made with heat-resistant plastic and reinforced with graphite fiber that uncovered the need for tougher plastics.

Impacts such as a bird flying into an airplane wing, or even a wrench falling onto a part, would shatter the plastic and leave behind only the woven graphite fibers, Lannutti said.

Still, the brittle plastic's tolerance of temperatures up to 800°F makes it ideal for parts surrounding hot jet engines.

In laboratory tests, the plastic-silica composite material retained the heat-resistance of fiber-reinforced plastics, but improved resistance to impacts by four to five times.

Lannutti said the new composite isn't as hard as steel, but displays good heat resistance at a fraction of the weight of steel.