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How rapid must biodegradability be? Let the standards decide

Article-How rapid must biodegradability be? Let the standards decide

One reader takes exception to comments in our December 2008 article on thermoformers’ distrust of biodegradable or bio-based plastics.

One reader takes exception to comments in our December 2008 article on thermoformers’ distrust of biodegradable or bio-based plastics.

MPW's December 2008 article “Processors wonder, how sustainable is sustainability” contains statements that perpetuate misinformation, specifically this quote from a sheet extruder serving the thermoforming market: “A ‘biodegradable’ plastic must disintegrate in 12 weeks, period, or must achieve significant amounts of biodegradation within 180 days.”

My response is based upon my background as an engineer and scientist.  I hold a degree in chemical engineering from the University of California at Santa Barbara.  I previously worked as an environmental engineering consultant for a major petrochemical company, Department of the Navy, Department of Defense, and private military contractors. My major focus was to work with the U.S. Navy to develop a commercial application for a bacteria strain known as dehalococcoides ethenogenes that degrades chlorinated solvents to harmless byproducts.

“Biodegradable” describes a process without a defined timeframe. It can take place in many environments, including soils, compost sites, landfills, water treatment facilities and even the human body. While the concept of biodegradation may be confusing, the word biodegradable is not complicated or confusing; if bacteria can break down a substance, then it is biodegradable.

Global standards exist today for compostable plastics (ASTM D6400) and compostable packaging (ASTM D6868). These standards contemplate activity in controlled composting conditions, found only at industrial composting facilities. These standards establish a degradation timeline of 180 days.

Apparently the aforementioned comment in the December article referred specifically to this particular set of criteria. The important distinction is products meeting these standards only do so under very controlled conditions. It is uncertain if biodegradation of these products will occur in 180 days in a landfill or even a backyard compost pile, so unless the consumer has access to commercial compost facilities, the compostable feature of their product is unlikely to produce meaningful results. When conveying biodegradable properties to a product, the standard under which it is declaring its biodegradability should be referenced.  

Many may remember Dr. William Rathje (Ed. note: a famous anthropologist probably best known for the Garbage Project, which he established in 1973 at the University of Arizona). Rathje conducted archaeological digs at landfills, only to find intact 30-year old newspapers, carrots and hot dogs – the sort of items most would have thought would degrade. In fact, most landfills are designed to reduce biodegradation activity.

Enhanced polymer-based products are finding their way into the market. These appear to accelerate the rate of biodegradation under the least desirable of environments (entombed in a landfill), without leaving harmful residue. Test standards to assess the biodegradation characteristics of these enhanced polymer-based products are under development.  These standards will establish the performance criteria required for degradation in landfill-like conditions. 

This new generation of biomaterials will deliver another sustainable option to the market.  Cost-effective and energy-efficient, they are based on existing polymer systems, so in-use physical properties are unaffected, while delivering accelerated biodegradation properties when disposed.

Instead of saying that a material must break down in 180 days to be biodegradable, I think that it is time to take a step back and look at the big picture. New ASTM standards should be developed that take into account the breakdown rates of the enhanced material when compared to its non-enriched compostable counterparts. We all serve as stewards of our environment. Our work and comments in this area should be aimed at ensuring any claims, whether of biodegradation or other characteristics, are fact-based and unassailable.

The author, Ben Porter, is a researcher with EDS Group Inc. (Mansfield, MA), an internationally active plastics processor and packaging design expert, with one of its business units specializing in reusable/returnable thermoformed packaging.

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