Our recent webcast, "A New Life for Plastics: End-of-life Solutions in the Age of Greener Materials," drew a sizeable audience -- and a sizeable number of questions. We only were able to address a handful of them during the webcast, so we asked the three participants -- William Hoffman, environmental scientist in green chemistry at UL Environment; Robert Whitehouse, Director of Applications Development for Metabolix, Inc., a leading bioplastics company; and Kelly Lehrmann, consultant with the German bioplastics firm FKuR -- to respond to some of the remaining questions.
Here are their thoughts on the benefits of bioplastics, the differences among various biobased plastics, the role of municipal waste agencies in creating a composting infrastructure, and other things.
The archived webcast is available for listening here. Access is free, though registration is required.
What is the best benefit from a bioplastic: the biodegradability or the renewable source reducing the carbon footprint?
William Hoffman: Not all bioplastics are biodegradable. Braskem (Green PE) and PolyOne (ReSound) both produce biobased materials which are not biodegradable. Ultimately, the "right" answer to this question would depend on the application for which the material is designed (and the end-of-life associated with that application). Let's say the material is to be used in a durable application, perhaps an appliance housing where that part needs to last the life of the appliance (approximately 10 years), then biodegradability is not an ideal characteristic. On the other hand, if the material is used in a disposable packaging application, biodegradability would be a desirable characteristic of the end-product since so much single-use plastic packaging end up in landfills.
Robert Whitehouse: The best benefit is a bioplastic that is both biobased and biodegradable. As an example, Mirel™ bioplastics is made from annually renewable resources, corn sugar, and is biodegradable in a wide range of environments including natural soil and water environments, in home and industrial compost facilities where available, and anaerobic digestion. The combination of biobased and biodegradable helps to reduce reliance on petroleum and can help to reduce the amount of waste sent to landfills or incineration.
What about anaerobic degradation in a closed landfill?
WH: Once a landfill is closed, the conditions that encourage biodegradation – recirculating leachate, which carry microbes and elevated moisture levels are removed. Indeed, closed landfills resemble the "dry tombs" that William Rathje studied in his Garbage Project in the 1970s.
RW: Landfills are typically unmanaged with regard to microbial activity and so degradation is very difficult to predict. Managed anaerobic degradation facilities typically take from 20 to 50 days for organic carbon conversion.
How long does it take ASTM D6400 to fully degrade into safe emissions in comparison to the other biodegradable products?
RW: ASTM D6400 was developed around the typical yard waste composting process of around 90 days.
What happens to the CO2 that's produced during the degradation?
RW: It is sequestered in making new plant-based crops.