Just One Word

Plastic wrap. Credit: Flora Lichtman/Science Friday

Tuesday, April 3rd, 2007--

There may indeed be a great future in plastics. Robson Storey, a researcher at the School of Polymers and High Performance Materials at the University of Southern Mississippi, is working on a recipe for a plastic that dissolves in seawater.

Storey says: “It’s a matter of economics, but as oil continues to become more scarce and more expensive, these sustainable new technologies will become more economically important.” Storey presented the plastic research at the meeting of the American Chemical Society last week in Chicago.

The military, which funds the project, is specifically interested in biodegradable stretch wrap. When food and other supplies are loaded onto a ship, they are stacked on wooden boards, called pallets, and covered in a plastic wrap. The plastic then has to be stored on board the vessel. If it were biodegradable in seawater, it could be thrown overboard.

“Understand no one will ever be throwing gobs of wadded up stretch wrap in the ocean,” Storey says. “I don’t want to give you the idea that we’re going to be throwing trash into the water.” Instead, the plastic would be ground up into a powder, mixed with seawater on board the ship and pre-degraded before being pumped overboard.

Plastics are made of polymers and biodegradable polymers are not new—they have been used for years for sutures and other biomedical applications. But to make these polymers into stretchy, soft plastic, Storey has to add ingredients, which complicates the degradation process.

Plus, these polymers dissolve very slowly in seawater, compared to soil or freshwater, Storey says. “Water from the ocean doesn’t tend to enter the plastic as well. The water likes to stay out in the salt.” But the degradation can be sped up by blending water-loving molecules like carboxylic acid into the plastic. So far, Storey has created a plastic that starts to break down after about five months in salt water. “It obviously is degrading because it gets crumbly and brittle—and that occurs within 5 months,” he says. He has yet to make it fully disappear.

Another challenge is preventing the plastic from degrading too quickly. “One critical problem is that if you create a stretch wrap that will dissolve in the ocean, how do you keep it from dissolving in the rain?” A potential solution is to engineer the plastic so the degradation is triggered by salt or the presence of marine organisms, Storey says.

If the plastic is going to be tossed overboard, it has to degrade into something that isn’t toxic. The biomedical polymers break down into carbon dioxide and water. “They are truly non-toxic, to the point where your body can handle them.” Storey's plastic has other byproducts: they are "proposed to be non-toxic, but we're going to have to prove that." He hopes that the final product will degrade into carbon dioxide, water and nutrients that marine organisms can use.

But even if the byproducts are shown to be fish-friendly, plastic-dumping has to first be made legal. Storey says: “It is against international maritime law to dump plastics in the ocean.” The MARPOL Convention forbids throwing any plastic into the sea, no matter how degradable. But Storey is hopeful: "If we develop something that will degrade in the marine environment, then someone is going to want to start using it. And that's when sanctioning bodies are going to say, 'we better look at this and make some decisions here.'"

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--Flora Lichtman