Here's a common question -- what kind of plastic is "greenest." A researcher at the University of Pittsburgh has compared a variety of plant-based polymers -- along with some traditional commodity thermoplastics. The results indicate the biopolymers are not necessarily better for the environment than traditional plastic materials -- mainly because conventional plastics can be environmentally less taxing to produce. The analysis was conducted by Michaelangelo Tabone, who did the study as an undergraduate student in the lab of Amy Landis, a professor of civil and environmental engineering in Pitt's Swanson School of Engineering. The research team first performed a life-cycle assessment on each polymer's preproduction stage to gauge the environmental and health effects of the energy, raw materials, and chemicals used to create one ounce of plastic pellets. Then they checked each plastic in its finished form against principles of green design, including biodegradability, energy efficiency, wastefulness, and toxicity. Conventional plastics took the top spots in the life-cycle assessments -- polypropylene was No. 1, followed by high density polyethylene and low density PE. A biopolymer polyhydroxyalkanoate -- placed No. 4. According to the researchers, bio-based plastics scored poorly because of the pollution they create during the manufacturing process.
The team attributed this to agricultural fertilizers and pesticides, extensive land use for farming, and the intense chemical processing needed to convert plants into plastic. All four biopolymers were the largest contributors to ozone depletion.Once in use, however, the biopolymers "cleaned up." Looking at the green design criteria, bioplastics took all the top positions: Two varieties of polylactic acid took the No. 1 and No. 4 spots, and two varieties of polyhydroxyalkanoate tied for No. 2. Biodegradability, obviously, was a big advantage for the bio-based resins on the green design scale. And, using that as a criteria, conventional plastics took a beating. PP, for example, sank to ninth place as a "sustainable" material, judged by the green design criteria. Their research will be published in the journal Environmental Science & Technology.