Ohio State University engineers have found a way to make dense plastic foam that may replace solid plastic in the future. The engineers are also said to have developed manufacturing techniques to eliminate the use of chlorofluorocarbons (CFCs) in foam production.
The potential market for this technology is huge, because plastic foam touches nearly every aspect of modern life, said L. James Lee, professor of chemical engineering at Ohio State. Common products include seat cushions, carpet padding, home insulation, disposable diapers, fast food containers, coffee cups and packaging material.
These 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 mould.
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 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 aluminium 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.
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 a supercritical fluid. Such fluids behave like both a gas and a liquid. They heated the carbon dioxide to 120 degrees Centigrade 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
The ultimate goal is to create plastic foam that is strong enough to replace solid plastic in structural applications, such as car or aeroplane panels, said Lee.