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Article contributed by Ramani Narayan, University Distinguished Professor, Michigan State University Department of chemical engineering & materials science feedstock, there is an intrinsic net 314 kg CO 2 (85.7% fossil carbon) or 229 kg of CO 2 (62.5% fossil carbon) released into the environment respectively at end-of-life. However, if the polyester or polyolefin is manufactured from a biofeedstock, the net release of CO 2 into the environment is zero because the CO 2 released is fixed immediately by the next biomass cycle. This is the fundamental intrinsic value proposition for using a bio/renewable feedstock and is totally lost or ignored during LCA discussions. Incorporating biocontent into plastic resins and products would have a positive impact – reducing the carbon footprint by the amount of biocarbon incorporated, for example incorporating 30% biocarbon PLA content into a fossil based polypropylene resin would intrinsically reduce CO 2 emissions by 42%. These are significant environmental value gains for the biobased product. It is equally important to note that in the conversion of the feedstock to product and in its use and ultimate disposal, ‘carbon’ in the form of energy is needed and releases CO 2 into the environment. Currently, in the conversion of biofeedstocks to product, for example corn to PLA resin, fossil carbon energy is used. The CO 2 released per 100 kg of plastic during the conversion process for biofeedstocks as compared to fossil feedstock is in many cases higher, as in the case of PLA. However, in the PLA case, the total (net) CO 2 released to the environment taking into account the intrinsic carbon footprint as discussed in the earlier paragraph is lower, and will continue to get even better, as process efficiencies are incorporated and renewable energy is substituted for fossil energy (see fig 3, these are actual data from Vink et al, www.natureworksllc.com and the APME database). For PLA and other biobased products, it is important to calculate the conversion ‘carbon costs’ using LCA tools, and ensure that the intrinsic ‘neutral or zero carbon’ footprint is not negated by the conversion ‘carbon costs’ and the net value is lower than the product being replaced from feedstock to product or resin manufacture. Biocarbon content determination: In order to calculate the intrinsic CO 2 reductions from incorporating biocarbon content, one has to identify and quantify the biobased carbon content. bioplastics MAGAZINE [05/08] Vol. 3 41
Basics As shown in figure below, 14 C signature forms the basis for identifying and quantifying biboased content. The CO 2 in the atmosphere is in equilibrium with radioactive 14 CO 2 . Radioactive carbon is formed in the upper atmosphere through the effect of cosmic ray neutrons on 14 N. It is rapidly oxidized to radioactive 14 CO 2 , and enters the Earth‘s plant and animal lifeways through photosynthesis and the food chain. Plants and animals which utilise carbon in biological foodchains take up 14 C during their lifetimes. They exist in equilibrium with the 14 C concentration of the atmosphere, that is, the numbers of C-14 atoms and non-radioactive carbon atoms stays approximately the same over time. As soon as a plant or animal dies, they cease the metabolic function of carbon uptake; there is no replenishment of radioactive carbon, only decay. Since the half life of carbon is around 5730 years, the fossil feedstocks formed over millions of years will have no 14 C Carbon Footprint Including Conversion signature. Thus, by using this methodology one can identify and quantify biobased content. ASTM subcommittee D20.96 CO2 has released codified during this methodology coversion into a test method (D 6866) to quantify biobased content. D6866 test method involves combusting the test material in the presence of oxygen to produce carbon dioxide (CO 2 ) gas. The gas is analyzed to provide a measure of the products. 14 C/ 12 C content is determined relative to the modern carbonbased oxalic acid radiocarbon standard reference material (SRM) 4990c, (referred to as HOxII). 700 600 500 400 300 End-of-Life Option: PLA, PLA blends and similar biobased plastics end-oflife scenario involves recycling, waste to energy plants or 200 biological disposal systems like composting or anaerobic 100 digestion. In each case, the biocarbon conversion to CO 2 is fixed by the next season biomass plantation giving it the 0intrinsic value proposition as discussed in detail earlier. However, many LCA studies show landfills as an end-of-life Fig 3 option for PLA and similar biobased plastics. The studies assume breakdown of the biocomponent anaerobically to methane with its attendant negative global warming Biocarbon content determination: Starch PET PP (85.71%c) effect. However, landfills are not the preferred end-of-life option for any waste, and efforts at all levels are underway to divert waste from landfills to making more useful product. It is also important to note that biodegradability is many times erroneously assumed for all biobased plastics. Not all biobased plastics are biodegradable, and not all biodegradable plastics biobased. Furthermore, the use of the term biodegradability is very misleading and deceptive if one does not define the disposal environment and the time to be completely assimilated by the microorganisms present in the disposal environment. Harnessing the power of microorganisms present in the disposal environment to completely (the key word being completely) remove the plastic/product from the environment via microbial assimilation (essentially food for the microorganisms) is a safe, efficacious, and environmentally responsible way to handle our waste products – the concept of biodegradable plastics. However, one must demonstrate complete feedstock removal CO2 in release one year or less via microbial assimilation in the selected disposal environment as codified in any of the ASTM D6400, EN 13432, and ISO 17088 standards. As reported by us, and clearly documented in literature, there is serious health and environmental effects if there is not complete removal (biodegradation) of the plastic from the environmental compartment. In summary, reporting the carbon and environmental footprint of PLA, PLA based products, and similar bioplastics and biodegradable plastics requires a clear understanding of the intrinsic carbon value proposition, the use of biocarbon content to quantify this value proposition and the appropriate use of LCA tools to report on the total environmental footprint. (from a presentation at the 1st PLA World Congress, 9-10 Sept. Munich, Germany) narayan@msu.edu 14 CO2 12 CO2 Solar radiation 14 C signature forms the basis to identify and quantify biobased content -- ASTM D6366 Biocarbon content Biomass/biobased feedstocks ( 12 CH 2 O) x ( 14 CH 2 O) x > 10 6 years Fossil feedstocks -- Petroleum, Natural gas, Coal ( 12 CH 2 ) x ( 12 CHO) x References: 1. Ramani Narayan, Biobased & Biodegradable Polymer Materials: Rationale, Drivers, and Technology Exemplars; ACS (an American Chemical Society publication) Symposium Ser. 939, Chapter 18, pg 282, 2006; Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) (2005), 46(1), 319-320 2. Ramani Narayan, Rationale, Drivers, Standards, and Technology for Biobased Materials; Ch 1 in Renewable Resources and Renewable Energy, Ed Mauro Graziani & Paolo Fornasiero; CRC Press, 2006 3. R Narayan, Proceedings ‘Plastics From Renewable Resources’ GPEC 2005 Global Plastics Environmental Conference - Creating Sustainability for the Environment, February 23-25, 2005 42 bioplastics MAGAZINE [05/08] Vol. 3
