COLUMBUS, Ohio -- Ohio State University engineers have found a way to make dense plastic foam that may replace solid plastic in the future.
The engineers have also developed innovative manufacturing techniques to eliminate the use of chlorofluorocarbons (CFCs) in foam production.
The announcement may provide a boost to the $2 billion per year American plastic foam industry. While the industry is trying to develop new applications for foam, it must also meet new international environmental standards that will go into effect in 2010.
L. James Lee, professor of chemical engineering at Ohio State, described his foam research in a presentation at the Materials Research Society annual meeting in San Francisco.
There he and his colleagues unveiled a dense new foam material reinforced with tiny clay particles. They also reported early success in their efforts to replace the CFCs in plastic foam with carbon dioxide.
The first part of Lee's presentation concerned nanocomposites, materials that contain particles of additives that measure only a few nanometers, or billionths of a meter, across.
Nanocomposites have recently attracted attention in the auto industry, where manufacturers are now using additives like clay to make lighter plastic parts.
Lee's nanocomposite plastic foam would be even lighter than these current nanocomposites, which are made from solid plastics.
"Many scientists are interested in nanocomposites, and many others are interested in creating strong plastic foams," Lee said.
"We thought if we brought those two concepts together, we would at least be able to give manufacturers more flexibility in designing foam products."
Lee's colleagues on this project include David Tomasko and Kurt Keolling, both associate professors of chemical engineering at Ohio State, and doctoral students Changchun Zeng and Xiangmin Han. With expertise in thermodynamics and polymer processing, the engineers were able to bridge the gap between nanocomposites and foams.
To the best of his knowledge, very few research groups are working on nanocomposite foams, Lee said.
The goal is to create plastic foam that is strong enough to replace solid plastic in structural applications, such as car or airplane panels, he said. Foam products would be lighter than solid plastics, but to the eye, they would appear the same.
The potential market for this technology is huge, because plastic foam touches nearly every aspect of modern life, Lee explained. Common products include seat cushions, carpet padding, home insulation, disposable diapers, fast food containers, coffee cups and packaging material.
These diverse products are all created the same way. Manufacturers inject gases, specifically chlorofluorocarbons (CFCs), into hot liquid plastic. The gas forms bubbles to plump up mixture, which then solidifies inside a mold.
When the gas bubbles are small and spread evenly within the material, the foam is stronger and denser, Lee said.
He and his colleagues found that if they added nanometer-sized clay particles to the liquid plastic, they could increase the foam's density. Small bubbles tend to form around the nanoparticles and cling to them.
"The nanoparticles are like seeds. We plant the seeds, and bubbles grow around them. The clay also thickens the plastic, which keeps the bubbles distributed uniformly inside," Lee said.
While most structural-grade plastic foam contains bubbles close to several hundred micrometers -- or millionths of a meter -- across, the bubbles in Lee's nanocomposite foams were as small as 5 micrometers across.
With a foam that contained 5 percent clay particles, the engineers were able to create boards that were just as strong, but only two-thirds as thick, as typical foam.
Since creating the clay nanocomposite foam, the engineers have started working on other additives, such as aluminum and carbon. Lee has applied for a patent for the technology, and an industrial partner has expressed interest in manufacturing larger quantities of the foam for further testing.
Several industrial partners are working with Lee and his colleagues to develop standard foams with carbon dioxide instead of CFCs, and Lee discussed the current state of that project in his conference presentation as well.
Other efforts to eliminate CFCs from plastic foam have failed, Lee said. "Carbon dioxide is more environmentally benign than CFCs," he explained, "but it's not the best foaming agent."
The Ohio State engineers found they could produce high-quality foam if they heated the carbon dioxide under pressure, until it became what is known as a supercritical fluid. Such fluids behave like both a gas and a liquid. They heated the carbon dioxide to 120ºC (about 250ºF) at a pressure of 1,200 pounds per square inch.
Lee said such temperatures and pressures are easy to obtain in industry. Manufacturers wouldn't even have to alter their existing foaming equipment, he said. What's more, carbon dioxide is inexpensive, costing only a few cents per pound.
Scientists have blamed CFCs for depleting Earth's atmospheric ozone, a layer of gas that blocks the sun's harmful ultraviolet radiation. To abide by the 1987 Montreal Protocol, the United States has committed to phase CFCs out of production by 2010.
The National Science Foundation funded this work, as did industrial partners of Ohio State's Center for Advanced Polymer and Composite Engineering.
Cite This Page: