A woody path to biodegradable plastics.

A woody path to biodegradable plastics

For thousands of years, people have used vast amounts of wood for such low-tech applications as building their homes and fueling their fires. But wood scientists, who think of wood as "three-dimensional biopolymer composites," want to see this age-old, renewable and biodegradable resource become the fount of high-tech materials, including plastics.

The U.S. pulping industry produces 20 million tons of lignin -- the complicated biopolymer that makes trees wood~ -- as a byproduct of paper making, says wood scientist Simo Sarkanen of the University of Minnesota in St. Paul. Virtually all of this lignin -- the second most abundant biological polymer on Earth -- gets burned as waste.

Sarkanen suggests that the huge, renewable stores of lignin could become feedstock for a wide range of biodegradable polymers. Lignin's complicated and only partially understood chemical structure -- involving up to three types of molecular units that can link in as many as 10 ways -- so far has discouraged researchers from developing lignin into a routine chemical basis for polymers and other higher-tech materials.

Although the chemical complexity of lignin in trees may be hopelessly daunting, the lignin that emerges from the pulping process appears to follow some structural rules, Sarkanen reports. For example, he and his colleague Sunil Dutta find that lignin components of specific molecular sizes link and dissociate in particular orders. Without disclosing details, Sarkanen says that he and co-workers already are using these rules to develop methods for casting films made of the lignin biopolymer. Since such polymers are nothing more than transformed wood, natural wood-eating microorganisms would make discarded lignin-based plastics disappear, he says.