Virginia Tech Researcher Reports Nano-particle Dispersion Technique Improves Polymers

But there are problems. "While 1 percent by weight of nano particleswill change a material's properties dramatically, 2 or 3 percentprovides hardly any additional enhancement," he said. "The particlesjust clump together, and thereby reduce the advantages associated withthe surface area of single particles."

Another problem is that the incorporation of nano particleschanges a polymer's flow properties leading to potential processingproblems.

Baird's research group at Virginia Tech has developed a methodfor improving the dispersion, or exfoliation, of individual nanoparticles into polymers. He will present his research at the 230thAmerican Chemical Society National Meeting, held in Washington, D.C.,Aug. 28-Sept. 1. "The paper will present how we are dispersing nanoparticles and how we are using flow properties to monitor dispersion,"he said.

Using supercritical carbon dioxide, the researchers are able toexfoliate nano particles at higher concentrations, leading to furtherenhancement of mechanical properties than presently possible using justmechanical mixing. "Carbon dioxide is soluble in a lot of polymers. Itattaches to the particles so they don't attach to each other, and helpsdisperse the particles throughout the polymer. It is a benign, naturalsubstance," Baird said.

The rheological properties including the normal stresses(elastic properties) and the stress relaxation response are used tomonitor particle dispersion.

The researchers also have discovered that the changed flowbehavior is good news -- an indication that the material will exhibitimproved mechanical properties.

Baird's team observed that nano clay particles well dispersedin polypropylene and polycarbonate plastics tend to promote polymerchain orientation, or alignment, and then retard relaxation or loss oforientation. "The result is they make the polymer chains act likelonger or higher molecular weight chains. The material is stronger thanone would expect given the size of a polymer chain."

Pointing to a bobbin of fiber, Baird said, "If that containednano particles and was stretched, it is possible that the fiber couldbe woven into a vest that would stop a bullet. An ordinary polymermaterial with well dispersed high levels (8 wt%) of nano particlescould have exceptional mechanical properties."

He will present the paper, "Effects of nano clay particles onnon-linear rheology of polymer melts (Poly 248)" at 11:20 a.m. Monday,Aug. 29, in the Grand Hyatt Constitution room D-E, as part of theHerman Mark Award program honoring Don Paul.

Learn more about Baird's research at http://www.che.vt.edu/baird/baird.htm