Researchers Seek Plastics From Fruit

Jan. 25, 2005 — -- Think of "plastic" and "fruit" and what pops into mind is probably an eye-catching bowl of artificial produce. But one day, the ties between the two may be a lot closer than just an artistic display of phony fruit.

Researchers at Cornell University in Ithaca, N.Y., have stumbled upon a novel discovery: Citrus fruits, such as oranges and lemons, could become a key building block to environmentally friendly plastics and polymers.

"Basically, all polymers that you come into contact with today are amazing materials," said chemistry professor Geoffrey Coates, leader of the Cornell research team. But "one of the concerns is that they are all made from oil. And most producers are using oil up faster than they're finding it."

So for the past seven years, Coates and graduate students Chris Byrne and Scott Allen have been concentrating on producing plastics from more sustainable, or renewable, sources. And the fruits of their work were published in a recent edition of the Journal of American Chemical Society.

A Fresh and Fruity Idea

The researchers describe how limonene, a carbon-based compound produced in more than 300 plants, could be a viable ingredient in producing plastic without petroleum.

The appeal of using this naturally occurring chemical, says Coates, is that commercial industries are already tapped into it for various other uses. Many common household cleansers, for example, get their fresh citrus scent from orange peel oil, which is composed of almost 95 percent limonene.

By combining the limonene with oxygen, the resulting limonene oxide becomes a reactive compound that could take the place of traditional petroleum-based chemicals.

The other key and readily available ingredient in Cornell's natural plastic is carbon dioxide, an atmospheric gas that has been growing due in large part to an increased use of fossil fuels.

But since both chemicals don't react on their own, Cornell's chemists had to develop a special zinc-based catalyst -- a chemical that sparks the reaction between the limonene oxide and CO2.

"The catalyst hooks them together like beads on a necklace," said Coates. "They make a string of molecules, alternating between limonene oxide and CO2, and create a polymer."

Plastic From Plants and Pollution

The new material, called limonene carbonate, shares characteristics similar to polystyrene, a petroleum-based polymer used in many common disposable plastics.

"It's a completely new polymer and the properties are still untested," said Coates, adding, "The point at which it softens -- roughly 100 degrees Celsius -- is similar to polystyrene."

While Coates and his team continue to study the material to see how compatible the new polymer may be to traditional plastics, the professor and others are optimistic about what the development could yield.

"Carbon dioxide is a greenhouse gas and contributes to global warming," said Coates. But "If you took all the CO2 out of atmosphere and made into plastic, we'd be up to our arms in plastics."

Turning Green to Save Some Green?

To be sure, the rush to develop green plastics isn't entirely new. Companies such as Cargill Dow in Minneapolis have been producing similar Earth-friendly polymers for years.

Its NatureWorks PLA and Ingeo materials, for example, are plastic made by fermenting starch from corn, wheat or oats. The lactic acid-based, biodegradable polymers are "sustainable" in that they rely on abundant food crops for raw material instead of diminishing petroleum supplies.

Company spokesman Michael O'Brien says there's been a "broad adoption" of its NatureWorks PLA and Ingeo plastics. Companies such as Del Monte and Newman's Own Organics use the plastics for packaging fresh produce and food, for example. But the company believes more companies will be making the switch to natural plastics soon, mainly because of cost.

"You've seen the prices in the petroleum industry rise and that's true of the plastics industry as well," said O'Brien.

But, he said: "There's no major price spike in corn. It's very stable, very abundant and we're running at a [price] rate where we can be efficient against PET [a common oil-based plastic]."

And while the company isn't intimately familiar with Coates' work, O'Brien says NatureWorks PLA is optimistic that there's room for yet another form of biologically created polymer.

"The thing to remember: there are a multiple number of polymers out there and bio-based polymers are the same way," he said. "It makes sense to use orange peel. It's a cheap material, abundant."

The Sticky Issues

Still, even Cornell's Coates is hesitant to say when or if limonene-based plastics will ever become commercially available. Coates does admit there are a few shortcomings that will still have to be accounted for as researchers continue to study the new bio-plastic.

For one, while carbon dioxide might be in bounteous supply, it's questionable whether there's enough limonene to go around.

"There's one-one-thousandth the quantity of limonene compared to petroleum," said Coates. "That's not a lot."

But rather than raid the world's supply of orange and lemon trees, Coates believes that other sources of limonene could step in. Turpentine and other "waste" from paper production -- such as pine tree bark, sap and resin -- could be converted into limonene. Tobacco plant leaves could also be genetically engineered to produce the carbon-compound as well, he says.

Another hurdle: The Cornell scientists still need to improve their zinc compound, which acts as the magic ingredient to blend limonene and CO2 into plastic.

"The catalyst that we use is fastest in the world at making these chemicals react," said Coates. "But significant work needs to be made to speed up process."

So for now, a fruit-based plastic still isn't quite ripe for commercial consumption.