Oxo-degradable plastics makers claim to have solution to industry's problem with conventional plastics, biodegradability; critics reject biodegradability claims, say material fails to meet ASTM D6400 standard for biodegradability
June 15, 2011
– Oxo-degradable plastic producers are claiming they have the cure for the public relations problem ailing the plastics industry—the issue of plastic waste and biodegradability, Chemical & Engineering News reported June 13.
Oxo-degradable plastics are made when salts of iron, cobalt and manganese are blended with plastics such as polyethylene, polypropylene and polystyrene. The salt additives spark the oxidative breakdown of polymer chains, and producers claim they break down polyethylene chains from a molecular weight of 250,000 to just 5,000, and at this weight, producers claim, the material can be bio-assimilated into the environment.
But the debate does not center on whether or not the additives break down polymers. The real issue is the end-of-life notion of biodegradability and exactly how that’s defined, according Ramani Narayan, professor of chemical engineering and materials science at Michigan State University. Eventually, everything breaks down, Narayan said, but to claim biodegradability in a meaningful way, producers should define the disposal environment, the time it takes to completely biodegrade, and finally, proof of complete biodegradation. The key measure of biodegradation is assessing chemically how much of the carbon in the material is converted to CO2 by microbes.
The American Society for Testing and Materials’ International’s Subcommittee on Environmentally Degradable Plastics & Biobased Products has developed standards for biodegradable plastics. Many consider the ASTM D6400 standard—a material must be converted into CO2 in composting conditions within 180 days—the true test for biodegradability.
The New York-based Biodegradable Products Institute, which performs testing of materials to certify satisfaction of ASTM standards, has certified 28 materials that meet the standard, including biobased plastics such as NatureWorks LLC’s polyactic acid, Novamont S.p.A.’s starch-based plastics, and Metabolix, Inc.’s polyhydroxyalkanoate.
Though oxo-degradables do biodegrade somewhat, they don’t come near to meeting the ASTM D6400 standard, according to Narayan, citing an example of a study where oxo-degradable plastic was in an open environment for a year and then composted for three months. It biodegraded by a little over 12%.
Critics take issue with oxo-degradable plastics producers claiming biodegradability, and California has even passed a law saying bags must meet the ASTM D6400 standard to be labeled biodegradable. The Federal Trade Commission is also considering mandates for biodegradability claims.
At least one PE producer, Brazil-based Braskem SA, has stayed away from oxo-degradable materials, and refuses to guarantee the performance of its products if they’re blended downstream with oxo-degradable additives.
The primary source of this article is Chemical & Engineering News, Washington, DC, June 13, 2011.