Biodegradable plastic clamshell food containers and compostable utensils already fill picnic baskets, and some furniture cushions contain foam partially made with soybean oil. These new plastics, which rely increasingly on corn and soy instead of petroleum for their material feedstocks, are often labeled as "green". That tag, as well as increasingly competitive costs in comparison with petroleum-based plastics, has drawn big names such as agriculture giant Cargill and Dow Chemical Co. to the bioplastics table.

Last year, U.S. domestic production of plastic resins—used for goods such as vinyl siding for houses and furniture foam—amounted to more than 113 billion pounds (lb). About 7% of a barrel of crude oil (the U.S. imports approximately 20,000 barrels a day) becomes plastic or other products. But processing that petroleum to make plastics takes more energy than processing vegetable oil, says Steve Robb, executive director of the Business and Technology Institute at Pittsburg State University (PSU), which is in Kansas. And vegetable oils, unlike petroleum, are a renewable resource.

"The thing that's in our favor [now] is the cost of the oils," Robb says, referring to castor and palm oil, in addition to soybean and others. "Soybean oil has remained at about the same price for the past several years, but [crude] oil has, of course, tripled in price".

The PSU researchers captured Cargill's attention with their biobased polymer research, eventually leading to the company's BiOH polyol, which substitutes soy-based polyols for up to 40% of the petroleum polyol that foam manufacturers routinely use to create spongy furniture stuffing. In a compacted R&D period (months instead of years), the researchers tweaked the polyol for the best durability and performance under heat and pressure.

Basic bioplastics

"There are different routes to the same endpoint," says Jeff Malsam, a chemical engineer who leads international business development for Cargill's BiOH polyols. "We think our molecule is difficult to duplicate, but there [are] lots of ways to hydroxylate a vegetable oil," he says.

Soybean oils vary in their structures and double-bond distributions; about 35 different types of triacylglycerides and functional groups are attached at different branching points. Methods to create molecules for a company's ideal plastic include monomerization, epoxidation with ring opening (using methanol, for example), hydroformylation, ozonolysis, transesterification, and direct oxidation.

Each method has drawbacks and benefits, said Zoran Petrović of the Kansas Polymer Research Center at PSU at a recent meeting in Brazil. Hydroformylation, for example, creates no waste byproducts, but the technique is expensive. Ozonolysis is very efficient, but it depends on electricity, which can drive up costs. Direct oxidation can be the cheapest, reducing the already lower costs of using biomaterials for plastics, and it allows for high functionality of the final molecules.

In Cargill's case, the chemists chose to hydroxylate soybean oils with a proprietary oxidation process. The company was "very concerned about oxidative side products that lead to odor; we manage those side reactions and remove the compounds pretty effectively," Malsam says.

Although being able to label its foam green is an added benefit for Cargill, that is not the whole story. "We liked that aspect, and thought our customers would like it, but the fundamentals are even broader than that," Malsam comments. In making bioplastics, Cargill takes advantage of its vertically integrated business structure by shipping the vegetable oils the company already produces to its processing plants and other companies. New bioplastics are an opportunity to leverage that infrastructure at a time when rising petroleum costs are opening up a market space, Malsam says.

Other products

In the past 5 years, Cargill and its wholly owned subsidiary NatureWorks have both won Presidential Green Chemistry Challenge awards, a U.S. EPA partnership to recognize innovation, for their products. NatureWorks first brought its bioplastics to market in 2002 in the form of hard resins for food containers. The company continues to work out the kinks, such as modifying bioplastics that cannot hold up to microwaving. And Cargill announced in August that it would open its own R&D lab to expand the uses of its polyols.

Meanwhile, the competition is growing for Cargill's polyol. At the 11th Annual Green Chemistry and Engineering Conference in June, David Babb of Dow presented information on scaling up production of foam with a natural polyol; he projected it should be ready for market later this year. Babb reported that Dow already has produced 250,000 lb of polyol in pilot trials and is ready to scale up its manufacturing.

These companies are not alone. Ford Motor Co. recently announced that it will have biobased foam in car seats in its 2008 Mustang. And smaller biotechnology companies, such as Metabolix (joined by Archer Daniels Midland) and Cereplast, have jumped into the fray, producing plastic picnic ware, for example, that biodegrades or can be broken down in large composting facilities.

Researchers continue to find ways to make bioplastics perform as well as or sometimes better than petroleum-based products. Depending on how they are made, bioplastics can be stable at higher temperatures or have more elongated fibers that prevent the foams from breaking.

Despite this flurry of activity and research, biopolymers currently hold only about 2–3% of the plastics market, according to Jim Martin of the nonprofit United Soybean Board, a farmer-led advisory board that funds promotion of and research on new uses for soybeans. In 2001, the organization provided several million dollars in seed money to Cargill, Dow, and a half a dozen other companies. By 2006, the companies had contributed additional research funding, bringing the total to nearly $14 million. At current rates, Martin estimates, bioplastics will make up 15% of the plastics market within a decade. But even technologically, "none of these materials are [a] 100% substitute" for petroleum-based products, he says.

A 90–100% replacement rate remains the goal for researchers at PSU and elsewhere, Robb says. But in the meantime, some companies are using only a tiny bit of vegetable-based feedstocks and labeling their plastics green. "To this point, nobody has defined what constitutes green. Technically, if it's 5% biobased, then it's a green product," says Robb. "One of these days, the federal government is going to come out and say it needs to have a certain percentage to be green."

Others emphasize that biobased products are not entirely green for other reasons. Some forms of soybean polyols require more toxic additives (such as isocyanate) to make them strong enough to compete with more typical petroleum plastics, researchers report. And a few companies, including Cereplast, are using nanoparticles to stabilize their biobased materials, notes Brenda Platt of the Institute for Local Self-Reliance, a nonprofit organization that promotes "zero waste". "That's letting the genie out of the bottle," says Platt, because researchers still haven't pinned down nanoparticles' environmental and human health effects.

"Just because it's biobased, is it more sustainable? The answer is no," says Mark Rossi of Clean Production Action, a nonprofit group that promotes green chemistry. Eco-friendly purveyors, such as the organic grocer Whole Foods Market, household-products maker Seventh Generation, and clothing manufacturer Patagonia, have "been really reluctant to accept PLA [polylactic acid plastics] as sustainable," Rossi says, because of concerns over agricultural pesticides, genetically modified organisms, and other practices related to soybean and corn production. Still, the "whole biobased question in general" presents a "real opportunity to make much greener materials, cradle to cradle."

Keeping it green

Less energy is required to produce soybean polyols and other vegetable-oil-based plastics than petro-products, Robb says. Cargill's preliminary life-cycle analyses show its BiOH polyols produce 36% less greenhouse-gas emissions and reduce total energy demand by 23% when replacing petroleum versions. According to calculations by a consulting firm hired by Cargill, 1 million lb of BiOH polyol saves about 2200 barrels of crude oil (nearly 700,000 lb). Add to this that soybeans and other crops are renewable resources, and "you don't have to worry about running out" of them, Robb notes, with cropland still available for growing plastic feedstocks.

Martin believes that biobased components will bring the U.S., which now imports petroleum-based chemicals at high rates, back to self-reliance from "chemical dependence." Their use may also result in a return to historic products such as linoleum, the canvas and linseed oil product that once graced 1920s kitchen floors, while scientists pursue new avenues for creating biobased plastics. —NAOMI LUBICK