Catalyst could enable biodegradable plastics

The standard catalysts used to make biodegradable plastics are metal-based, which are difficult or expensive to remove from the final material, and do not degrade in the environment.

The research group headed by Robert Waymouth of Stanford and James Hedrick of IBM Research presents an alternative catalyst made from common organic compounds.
The researchers crafted the catalyst by reacting common chemical ingredients – thiourea with a metal alkoxide.

The result is a catalyst that is both fast and selective, meaning that it excels at accelerating and facilitating reactions and that it doesn't alter the resulting polymer's shape or properties once it is formed.

"While many catalysts are either fast or selective, these catalysts are both," said Robert Waymouth, the Robert Eckles Swain Professor in Chemistry at Stanford. "They are simple to prepare, easy to use and can be readily adopted by anyone with a basic knowledge of chemistry."

In addition to lowering the cost and environmental impact, the new catalyst design is highly tunable, Waymouth said, and can be used to generate several varieties of plastics suitable for different functions.

The work can produce polylactic acid, a commercial compostable biodegradable polyester utilised in disposable plasticware, such as tableware, cups, plates and forks.

It also has medical applications for resorbable sutures, implants and stents, as well as biomedical implants and drug-delivery materials. Everyday items such as food packaging and non-woven fabrics are also a possibility.

Although the results are based on a decade of research, they are just the first steps, the researchers said. Because this technique is relatively simple and the catalysts are readily modified, these advances could lead to new and broadly useful class of catalysts – and likewise, new and useful biodegradable plastics – beyond what's been presented in this study.

"Our catalyst design is simple and general and could prove useful not only for polymerisation but for a wide range of organic reactions," said Xiangyi Zhang, the Stanford graduate student who conducted the experimental work.

In addition to Waymouth, Hedrick and Zhang, the study, "Fast and selective ring-opening polymerisations by alkoxides and thioureas," was co-authored by Gavin Jones of IBM Research. The research was funded in part by the National Science Foundation.