American Scientist

Although the plastics industry has depended predominantly on petrochemicals for feedstocks throughout most of its history, some early plastics were plant based. Parkesine, the first human-made polymer, was created by inventor Alexander Parkes in 1856 out of chloroform and castor oil. Henry Ford unveiled the now-legendary "soybean car," with soy-based plastic body panels, in 1941. Now, as the price of petroleum rises and concern mounts about the environmental effects of petrochemicals, the plastics industry is racing to create renewable polymers from bio-based sources.

At the ninth annual Bioplastics Conference, sponsored by European Plastics News and held last December in Cologne, Germany, the Brazilian petrochemical company Braskem received the top honor in the second Bioplastics Awards. Braskem announced last summer that it has developed a "green polyethylene" sourced entirely from sugarcane—a natural choice given that Brazil is the world's largest producer of sugar. Despite the recent bioplastics boom, this is the first time a substance exactly equivalent to petrochemical polyethylene has been produced from nonfossil sources. "What's taken everybody by surprise," says John Williams, technology-transfer manager at the U.K.'s National Non-Food Crops Center, "is the speed of development" of this material. "If you look back a few years, estimates put the development of polyethylene from nonpetrochemical sources at 2020."

To make the biopolymer, Braskem converts sugarcane-sourced ethanol into ethylene by a process called ethanol dehydration. This transfers 99 percent of the carbon in ethanol into ethylene, says Antonio Morschbacker, Manager of Technology for Green Polymers at Braskem. The main byproduct is water, which, when purified of contaminants (mainly ether and nonreacted ethanol), can be recycled. The ethylene is then polymerized. It would be impossible to tell Braskem's plastic from petro-polyethylene if not for a single difference: It contains trace amounts of the isotope carbon-14. Using the same process employed in radiocarbon dating, chemists can measure the amount of carbon-14 in plastic and use it to determine the percentage of biopolymer it contains. The ability to certify its bioplastic using ASTM International standards (in this case, ASTM D6866) gives Braskem a marketing edge. The material will be used in packaging for food and cosmetics, but Morschbacker expects the major application will be in the automotive industry, where the bioplastic will be used in injection and blow molding. Henry Ford's soybean car may well return, albeit in a slicker, smoother reincarnation.

"You can't argue with the fact that a bio-based plastic offers better possibilities for end-of-life treatment," says Williams. The carbon released from these plastics represents no net addition to the atmosphere, whereas the production and incineration of petrochemical plastics boosts CO₂ levels. Because Braskem's polyethylene is identical to fossil-based plastics, it can be recycled along with them, making it possible to integrate the new material into established recycling systems. This trait also makes it easier for producers to adopt the new polymer. According to Morschbacker, it can be processed using the same equipment and settings that companies use for petroleum-based polyethylene. The machinery will never know the difference. Incineration at high temperatures (900 degrees Celsius) also shows promise. And though the technology is still new and the number of plants small, some companies are also using catalysts or microwaves to convert the polymers into gasoline or diesel. This could be good news for the biofuels sector as well: Recycling bioplastics into fuel could allay concerns about the use of food crops in biofuels production.

Still, compared with biodegradable and largely biosourced polymers such as Mater-Bi, produced by the Italian company Novamont, Braskem's green polyethylene has slightly fewer end-of-life options. And Braskem's baby comes with the same toxicity issues as petrochemical plastics. Francesco Degli Innocenti, Ecology of Products and Environmental Communication Manager at Novamont, takes an equitable view: "Generally speaking, nonbiodegradable polymers seem to be more suitable for durable products (as durability could be impaired by biodegradability). For disposable items, biodegradability and compostability can be an advantage."

Novamont fared well at the Bioplastics Awards too. Several award-winning products, including sanitary pads and a printable plastic film for use in packaging, use Mater-Bi (the name stands for "Material Biodegradable") as a component. Plastic shopping bags—traditionally made with polyethylene—are another product being made with the material. This is great news for consumers who want to compost their food wastes—placing scraps in a biodegradable bag and chucking it in the compost pile eliminates the task of cleaning out the compost bucket.

As with any rapidly developing technology, the potential for false starts is there. Billiard balls coated with the early plastic collodion exploded on contact with one another. A recent example whose potential concerns Williams is that of degradable additives. Added to fossil-based plastics, they are designed to cause the plastics to fragment more quickly and prepare them for biodegradation by soil microbes. But Williams is not convinced they're a good idea. "The last thing you want is for a petrochemical plastic to degrade into CO₂," he says. "Why would you want to do that? It's like taking oil out of the ground and burning it—except in between you get to use plastic." And he has another worry: "I haven't seen any unbiased work that guarantees 100 percent degradation," he says. Small plastic fragments are hydrophobic and attract other hydrophobic particles—including pesticides and heavy metals—which can lead to bioaccumulation of toxic substances. If degradable additives were proved to be completely effective, however, they could be useful in providing end-of-life solutions for biobased plastics.

Williams is optimistic about future developments: "Let's face it—biobased plastics at the moment are in their infancy. As you scale up, efficiencies and energy balances become better."  Morschbacker agrees. "We have a big road to build," he says. "We'll look to life-cycle analysis to find the best options." Braskem is already hard at work: It has been operating pilot plants, which produce samples of the polymer for companies to test, for two years; large-scale commercial production is scheduled to begin in 2009. If both industry and independent research groups continue to show interest in these technologies, the results could be very promising indeed.