We already have plastics made from corn and sugar. Now, scientists have created a Styrofoam-like material using mostly milk proteins and clay.
Ultra-light and largely biodegradable, the plastic might some day become a green alternative to petroleum-derived foam packaging blocks, among other applications.
"The idea that we could go from milk and dirt to plastic foam seems attractive," said David Schiraldi, a polymer scientist at Case Western Reserve University in Cleveland. "Clay is pretty close to inexhaustible. Our only effluent is water vapor. It seems pretty green to me."
The research began with an accidental discovery in the lab. One of Schiraldi's students freeze-dried clay and got something intriguing enough to warrant a closer look. So, the team started mixing the clay with a variety of materials.
When they added a cow's milk protein called casein, they ended up with a super-light, fluffy, and foam-like material. With further experimentation, they hit on a recipe that worked well enough for publication in the journal Biomacromolecules.
"The process," Schiraldi said, "is simplicity itself."
The researchers start by throwing a scoop of clay and some water into a kitchen blender. Two minutes of mixing produces what Schiraldi's students call a clay smoothie.
Next, they add some casein powder, a dried version of the most common protein in milk. The final ingredient is a tiny amount of a glycerol-based material, which basically stiffens up the solution's chemical bonds.
After running the blender one last time, the scientists pour the dirty-looking water into molds and freeze them like ice-cubes. Then, they freeze-dry it get all the water out.
The result, Schiraldi said, is a material that has all the same properties of Styrofoam, but is 98 percent bio-based. At 100 degrees Celsius (212 degrees Fahrenheit), the milk-containing foam lets out a few drops of water. But it stays sturdy up to 200 degrees Celsius (392 degrees Fahrenheit).
In tests conducted by the U.S. Department of Agriculture, close to a third of the new material broke down after about 45 days in industrial compost conditions. That's a huge environmental leap beyond Styrofoam and other types of Expanded Polystyrene Foam, a category of materials that is often used as disposable packaging for electronics and other products.
"Compared to expanded polystyrene foam, we're in a different league," Schiraldi said. "Styrofoam lives forever."
The research spawned a brand new start-up company called Aeroclay, Inc., which is using the patented technology to develop practical products. Schiraldi imagines a plastic factory of the future that taps into vats of milk instead of oil.
Before milk-based plastics will go mainstream, though, there are technological hurdles to overcome. For example, scientists will need to make sure that the new material doesn't smell like sour milk.
There are also practical market pressures to contend with, said James McGrath, a chemical engineer at Virginia Tech in Blacksburg.
"It makes a nice quote to say this is going to replace polystyrene foam, but there are a lot of issues," McGrath said, "including economic ones and the price-to-volume relationship."
"It always looks good to come up with something like this," he added. "It's a very worthwhile objective to pursue."