Green Plastics: An Introduction to the New Science of Biodegradable Plastics

by E. S. Stevens. Princeton University Press, Princeton, NJ, 2002. Hardcover, 248 pages, $29.95.

Green Plastics is deceptive; this book covers much more than biodegradable plastics. Readers with interest in plastics or polymer chemistry will find a wealth of information on conventional—petroleum-based—plastics as well.

Author E. S. Stevens, a professor of chemistry at the State University of New York in Binghamton, has a rare gift for making complex chemistry understandable. In fact, this is the first place I’ve seen really clear explanations of basic polymer chemistry and terminology!

Part One of

Green Plastics provides an overview of plastics, addressing history, the basic chemistry of plastics, environmental issues relating to plastics, and what happens to plastics after use. Part Two addresses bioplastics. Here, readers learn about such natural polymers as cellulose, starch, agar, and chitin (all polysaccharides); lignin; various proteins including casein, whey, and soy protein; and natural polyesters produced by bacteria (some of which are used in biomedical applications). Also covered here are synthetic biopolymers, which are produced in factories but derived from natural materials. A recently publicized example of such materials is poly(lactic acid) or polylactide (PLA), which is being produced in a new Cargill Dow plant in Blair, Nebraska (see

EBN

Vol. 10, No. 7/8).

The biodegradability of plastics—and bioplastics in particular—is addressed in detail. Biodegradability is a property of certain synthetic plastics (especially those with oxygen molecules in the polymer chain), but it is one of the biggest selling points of bioplastics, in which biodegradability is very easy to achieve. Biodegradation is particularly important for such applications as six-pack rings that decompose in seawater and agricultural row-crop mulches that break down in soil. But biodegradability is a two-edged sword, since breaking down too rapidly compromises performance. Stevens explains how the degradability of plastics can be “programmed” by adjusting the formulation.

There is little coverage in

Green Plastics of the feedstocks and manufacturing impacts of different plastics, or disposal impacts other than degradation. This is too bad, as the issues can be quite contradictory. We at

EBN have often considered polyethylene and polypropylene among the cleanest plastics, for example (they contain only carbon and hydrogen and can be incinerated as cleanly as petroleum), but they are also among the least biodegradable of plastics.

An added bonus in the book for anyone with school-aged children in need of science projects is an appendix with recipes for making your own bioplastics out of such common ingredients as cornstarch, gelatin, and glycerol.

– AW