October 22, 2010
While polyvinyl chloride (PVC) and polycarbonate (PC) ranked last among 12 different petroleum- and biomass-based polymers evaluated by researchers at the University of Pittsburgh, using green design principles and lifecycle assessment (LCA) tools, the research also finds that biopolymers aren’t necessarily cleaner than the oil-based polymers, reports 3BL Media.
Polyethylene terephthalate (PET) also ranked at the bottom, according to the study, Sustainability Metrics: Life Cycle Assessment and Green Design in Polymers.
Although biopolymers are more eco-friendly, the farming and energy-intense chemical processing associated with them means they are dirtier to produce than petroleum-derived plastics, say researchers.
Still, biopolymers beat the other plastics for biodegradability, low toxicity, and use of renewable resources, say researchers.
In the LCA analysis, several of the biopolymers beat out PVC, PET and PC, but not the petroleum-based polyolefins, due to the intense energy, pesticide and land use currently practiced in industrial agriculture, reports 3BL Media.
The report finds that three petroleum-based plastics in the polyolefin class, high density and low density polyethylene and polypropylene, earned the top LCA ranking.
Many independent materials experts recommend that PVC, the most widely used in building products, and PC, be avoided in green products and green building, reports 3BL Media.
The research team first performed a LCA on each polymer’s preproduction stage to determine the environmental and health effects of energy, raw materials, and chemicals used to create one ounce of plastic pellets. They checked each plastic in its finished form against principles of green design, including biodegradability, energy efficiency, wastefulness, and toxicity.
The evaluation found that all four biopolymers were the largest contributors to ozone depletion. The two tested forms of sugar-derived polymer — standard polylactic acid (PLA-G) and the type manufactured by NatureWorks (PLA-NW), the most common sugar-based plastic in the United States, exhibited the maximum contribution to eutrophication, which occurs when overfertilized bodies of water can no longer support life, say researchers.
One type of the corn-based polyhydroyalkanoate, PHA-G, topped the acidification category. In addition, biopolymers exceeded most of the petroleum-based polymers for ecotoxicity and carcinogen emissions.
However, once in use, biopolymers beat traditional polymers for eco-friendliness, according to researchers. For example, the sugar-based plastic from NatureWorks jumped from the sixth position under the LCA to become the material most in keeping with the standards of green design.
Another finding showed that polypropylene (PP), widely used in packaging, was the cleanest polymer to produce, but sank to ninth place as a sustainable material.
The researchers also found that the petroleum-plant hybrid biopolyethylene terephthalate, or B-PET, ranked 12th as most harmful to produce and 8th to use.
Caveat: The Pittsburgh study notes that LCA is an inadequate tool for making final evaluations of building products due to significant data gaps and limited quality of existing data, and that LCA methods did not account for a wide range of significant issues such as incineration and many health impacts associated with the chemicals used in all plastics, reports 3BL Media.
The researchers also recommend that several key principles should guide materials policy in the green building sector, including that PVC and the other more complex petrochemical-based plastics have limited potential for improvements, and recycled polyolefins and bio-based materials raised with less toxic growing practices hold the best promise for truly sustainable material systems.