Researchers at the University of Pittsburgh evaluated the environmental impacts of 12 different polymers, both petroleum and biomass based, using green design principles such as the 12 Principles of Green Chemistry and the 12 Principles of Green Engineering, as well as conventional life cycle assessment (LCA) tools. Three of the polymers evaluated - PVC (polyvinyl chloride), PET (polyethylene terephthalate), and PC (polycarbonate) - "place at the bottom of both systems," according to the study, Sustainability Metrics: Life Cycle Assessment and Green Design in Polymers. Many independent materials experts recommend that two of these, PVC - the most widely used in building products - and PC, be avoided in green products and green building, as we did in the Plastics Environmental Preference Spectrum (Figure 1 below).
A new study from the University of Pittsburgh offers further support for the 2006 Plastics: Environmental Preference Spectrum developed by Tom Lent of the Healthy Buildign Network, and Mark Rossi of Clean Production Action, ranking polyolefins and sustainably grown bioplastics as preferable, and PVC consistently among the worst plastics for the environment.
Three petroleum-based plastics in the polyolefin class - high density and low density polyethylene and polypropylene - earned the top LCA ranking. Polyolefins are direct by-products of petroleum refining, requiring less chemical processing and additional toxic additives then the other petroleum-based plastics. In building products, polyolefin roofing membranes have long been considered an environmentally superior substitute for PVC membrane roofs.
A significant finding of the study is that simply replacing petroleum feedstocks with biofeedstocks raised by current standard agriculture practices does not necessarily reduce overall environmental impacts. In the LCA analysis, several of the biopolymers beat out the PVC, PET & PC, but not the petroleum-based polyolefins, due to the intense energy, pesticide and land use practiced in much industrial agriculture at present. The authors recommend that: "Principles regarding the use of renewable resources should be redefined to prevent trade-offs related to the use of harmful chemicals on crops and the energy/emissions in the production and use of fertilizers and pesticides."2 This finding affirms the recommendations in the Sustainable Bioplastics Guidelines developed by the Sustainable Biomaterials Collaborative of plastics purchasers, environmentalists and sustainable agriculture groups, including the Healthy Building Network.
Applying green design principles to estimate the potential for reducing each polymer's estimated life cycle environmental impacts during production, the researchers concluded that adhering to green design principles could reduce the environmental impacts of both petroleum polymer and biopolymer production. However, the potential improvement of plastics based on extraction of petroleum is constrained by the inherent chemical complexity of PVC, PC, polystyrene (PS) and PET, as well as the limits on existing oil reserves. Petroleum extracted from new reserves such as Canadian tar sands would drastically increase the global warming impacts of petroleum based plastics.
The Pittsburgh study also makes clear that life cycle analysis remains an inadequate tool for making final evaluations of building products due to significant data gaps and limited quality of existing data. The study noted that available life cycle assessment methods were not comprehensive and "have a limited scope,"3 failing to account for a wide range of significant issues such as, incineration, and many health impacts associated with the chemicals used in all plastics.
Despite its caveats and complexities, the University of Pittsburgh reaffirms several key principles that should guide materials policy in the green building movement over the long term:
PVC and the other more complex petrochemical based plastics have big impacts and limited potential for improvement
Recycled polyolefins and biobased materials raised with less toxic growing practices hold the best promise for the development of truly sustainable material systems
Key to realizing these potentials will be the application of green chemistry and engineering principles to material design, product and life cycles
In the meantime, the study is an important contribution to the body of evidence supporting recommendations that PVC and PC plastic be eliminated from green building to rid our buildings of the worst materials and encourage the development better options.
To learn more about these plastics and their associated environmental impacts go to www.pharosproject.net.
 Michaelangelo D. Tabone, James J. Cregg, Eric J. Beckman, and Amy E. Landis. "Sustainability Metrics: Life Cycle Assessment and Green Design in Polymers." Environ. Sci. Technol., Article ASAP DOI: 10.1021/es101640n
 Ibid, p.E.
 Ibid, p.E.