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Sci Tech
Strong, eco-friendly plastic foams
OHIO STATE University engineers have found a way to make dense plastic foam that may essentially replace solid plastic in the future.
The engineers have also developed innovative manufacturing techniques to eliminate the use of chlorofluorocarbons (CFCs) in foam production.
Researchers 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 the team's presentation concerned nanocomposites, materials that contain particles of additives that measure only a few nanometers, or billionths of a metre, across. Nanocomposites have recently attracted attention in the auto industry, where manufacturers are now using additives like clay to make lighter plastic parts.
The nanocomposite plastic foam would be even lighter than these current nanocomposites, which are made from solid plastics.
With expertise in thermodynamics and polymer processing, the engineers were able to bridge the gap between nanocomposites and foams.
The goal is to create plastic foam that is strong enough to replace solid plastic in structural applications, such as car or airplane panels.
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.
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 mould.
When the gas bubbles are small and spread evenly within the material, the foam is stronger and denser. The team found that if they added nanometre-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.
While most structural-grade plastic foam contains bubbles close to several hundred micrometers or millionths of a meter across, the bubbles in the nanocomposite foams were as small as 5 micrometers across.
With a foam that contained 5 per cent 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. Several industrial partners are working with Lee and his colleagues to develop standard foams with carbon dioxide instead of CFCs.
The team 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. They said such temperatures and pressures are easy to obtain in industry. The researchers further add that manufacturers wouldn't even have to alter their existing foaming equipment.
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