Treading lightly

The pressure is on for designers to pick materials that will leave little to no environmental footprint at the end of a product's useful life. Product designers have historically focused on performance and how much it will cost to mold parts when spec'ing engineering resins. With FEA and CAE software, it's easy to narrow the field of options based on mechanical, thermal, and physical performance. But these tools won't tell designers about the environmental footprint the various resins (including fillers, additives, and reinforcements) leave at the end of a widget's useful life. "Environmental responsibility requires that designers look at the entire product cycle from basic feedstock to ultimate disposal from a holistic point of view," says Ramani Narayan, professor chemical & biochemical engineering at Michigan State University. Biodegradability is a big part of biobased polymers' appeal. These renewable resource-derived plastics (as opposed to petroleum-based plastics) can be disposed of through composting, soil application, and biological wastewater treatment. This makes them prime candidates for use in short-life and disposable consumer goods and packaging. "To use them, however, designers must engineer products so they retain the material's biodegradability," says Narayan. "For durable products, biobased materials are also an option, but need to be engineered for performance and long life which may impact how well the material will biodegrade." "Biodegradation of natural materials (including biodegradable plastics) produce valuable compost as the major product, along with water and CO ," says Narayan. "But the CO produced doesn't contribute to an increase in greenhouse gases because it is already part of the biological carbon cycle." But polymers have historically been designed to resist degradation as happens in a compost heap. "The challenge," says Narayan, "is to design polymers that have the necessary performance during use, but destruct under the stimulus of an environmental trigger