Measuring Biobased Carbon Content

C-14 signature forms the basis of Standard test method to quantify biobased content (ASTM D6866) 

The CO2 in the atmosphere has COi in equilibrium with radioactive CO2. Radioactive carbon is formed in the upper atmosphere through the bombardment of cosmic ray neutrons on N. It is rapidly oxidised to radioactive C02 and enters the Earth s plant and animal life through photosynthesis and the food chain. Plants and animals that use carbon in biological food chains take up C during their lifetimes. They exist in equilibrium with the C concentration in the atmosphere that is, the numbers of C-14 atoms and nonradioactive carbon atoms stay approximately the same over time. As soon as a plant or animal dies, the metabolic fimction of carbon 

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Inorganic carbon like calcium carbonate is excluded from the calculations and in the ASTM D6 8 66 method for measuring biobased carbon content, any carbonate present is removed before measuring the biobased carbon content. 

Summary This American test method establishes the procedures, equipment, materials, and condihons to measure the carbon content of the plastic sample through radiocarbon analysis. This test method is applicable to carbon-based plastic products that can undergo combushon in the presence of oxygen to produce carbon dioxide gas (CO2). This test method can be useful for companies and US federal agencies to promote the use of biobased products in commercial, non-food products. The test method directly discriminates between 14C/12C content of plastic samples made from contemporary carbon and those plastic samples made from petroleum sources that do not have 14C. Measurement of a plastic product s 14C/12C content is determined relative to the modem carbon-based oxahc acid radiocarbon Standard Reference Material 4990c. 

Figure 16.7 Measuring the biobased carbon content using radiocarbon analysis. Reproduced with permission from R. Narayan, Biobased Biodegradable Polymer Materials Rationale, Drivers, and Technology Exemplars, American Chemical Society Symposium Series 1114, 2012, p.l3 and American Chemical Society Symposium Series 939, 2006, p.282. 2006, American Chemical Society...

DIN CEN/TS 16137 DIN SPEC 91236 Measuring the biobased carbon content of plastics and other polymers... 

The biobased content of the plastic material can be established by tests that measure carbon isotopes of the polymer material. In the United States, the ASTM D6866 standard estabUshes the procedures, equipment, materials, and conditions to measure the 14C content of the plastic sample through radiocarbon analysis. ASTM D6866 biobased standard establishes that a material can be certified as biobased if greater than 99% of the carbon in the plastic sample is made from organic sources and is characterized by a 14C isotope. This will be further explained in Chapter 8. 

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