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bioplasticsMAGAZINE_1306

Basics kg of CO 2

Basics kg of CO 2 removed per kg of resin 3.5 3.14 3.0 2.5 2.29 229 2 2.0 1.87 187 1.5 1.0 0.5 0 Experimentally determined using ASTM D6866 based on the principle of 12C/14C analysis Bio-PE / -PP Bio-PET PLA PE / PET Figure 4. Material carbon footprint, illustrating amount of CO 2 removal from the environment and incorporating into polymer 0 Biobased carbon content A key requirement for biobased plastics is the need for a transparent and accurate test method to unequivocally identify and quantify biobased carbon present in the plastic. Recall that biobased plastics are plastics made from plant biomass which have recently fixed CO 2 present in the environment (new carbon – see Figure 1). The carbon dioxide (CO 2 ) in the atmosphere has 12 CO2 in equilibrium with radioactive 14 CO 2 . Plants and animals that use carbon in biological food chains take up 14 C during their lifetimes. They exist in equilibrium with the 14 C concentration in the atmosphere; that is, the numbers of 14 C atoms and non-radioactive carbon atoms stay approximately the same over time. As soon as a plant or animal dies, the metabolic function of carbon uptake ceases; there is no replenishment of radioactive carbon, only decay. Since the half-life of carbon is around 5730 years, the petro-fossil feedstock formed over millions of years will have no 14 C signature. However, all biobased plastics will have this small but measurable 14 C signature associated with it. This forms the basis to identify and quantity the percent biobased carbon in the product. The test method calls for combusting the biobased plastic and analyzing the CO 2 gas evolved to provide a measure of its 14 C/ 12 C content relative to the modern carbon-based oxalic acid radiocarbon standard reference material (SRM) 4990c (referred to as HOxII). This methodology to determine bio-based carbon content has an accuracy of +/–3% and was first codified into an ASTM standard D6866 titled “Standard Test Methods for Determining the Biobased Content of Solid, Liquid, and Gaseous Samples Using Radiocarbon Analysis”. This test method also forms the basis for determining biobased carbon content in the EN and ISO standards. Percent biobased carbon content = mass of biobased (organic) carbon /total mass of (organic) carbon * 100. Inorganic carbon like calcium carbonate is excluded from the calculations and in ASTM D6866 method for measuring biobased carbon content, any carbonate present is removed before measuring the biobased carbon content. However, EN, and ISO standards also provide for reporting percent biobased carbon content using total carbon present in the plastic – that is without removing the inorganic carbonates. Percent biobased carbon content TC = mass of biobased (organic) carbon /total mass of carbon * 100. It should be noted that the principle and methodology is the same, the biobased carbon content value obtained would be different depending on whether one used total mass of organic carbon or total mass of all carbons present in the plastic. The percent biobased carbon content using radiocarbon analysis like in ASTM D6866 gives the ratio of the mass of biobased (organic) carbons to total mass of (organic) carbons or total mass of all carbons present in the product, for example if 52 bioplastics MAGAZINE [06/13] Vol. 8

Basics a product A contains 60% biobased carbon, it means that for every 100 kg of carbon present in product A there are 60 kg of biobased carbon. It is not that for every 100 kg of Product A, there is 60 kg of biobased carbon! This is because product A includes elements other than carbon, like hydrogen, oxygen, and other elements. This does not pose a problem, because it is straightforward and well established method in organic chemistry to experimentally determine elemental analysis – which gives the percent carbon present in product. In the above example let us assume that elemental analysis of Product A gives us 50% organic carbon; 5% hydrogen, and 45% oxygen -- in other words 100 kg of Product A contains 50 kg of carbon. If the biobased carbon content determined experimentally (using ASTM D6866) is 60%; then 100 kg of Product A will contain 30 kg of biobased carbon [60/100 *50] This can be extended to calculating the biobased carbon content of a complex product comprising n components as shown in the equation below. However, the biobased carbon content (using ASTM D6866), organic carbon content, and mass of each of the n components should be known. Alternatively, the complex product can be directly tested for biobased carbon content using ASTM D6866. BCC (product)= ∑w n *BCC n *OCC n /∑w n *OCC n w n = mass of the n th component BCC n = biobased carbon content of n th component OCC n = organic carbon content of the n th component Biobased mass content The earlier discussion showed calculations based on carbon mass. This seems logical given that the value proposition for using biobased plastics arises from carbon footprint reductions (CO 2 removal from the environment) achieved. The biobased carbon content calculations can readily provide the CO 2 reductions obtained as discussed in the earlier sections. It may be useful to report the biobased mass content (not just on a carbon content basis) for better communication and understanding by general audiences and to satisfy other requirements. However, there is no verifiable, accurate test methodology that can directly measure the biobased mass content of a product. To calculate and report total biobased mass content of a plastic product, one needs to experimentally measure the biobased carbon content, and know the chemical structure of the polymer material (the chemical structure should be validated by established chemical and spectroscopic techniques). This is best illustrated with the biobased PET bottles and containers in commercial use today. PET has the chemical structure shown below: –CO-C 6 H 4 -CO - O-CH 2 -CH 2 -O Fossil based acid 8 carbon atoms 68.75% by mass 20% biobased carbon content (ASTM D 6866) 31.25% by mass/weight of plant biomass The biobased PET is made from the condensation polymerization of fossil based terephthalic acid and biobased ethylene glycol. So, there are 2 biobased carbons and 8 fossil carbons in the product giving it 20% biobased carbon content. Any PET bottle in the market can be collected and experimentally analyzed (ASTM D6866) for biobased carbon content as discussed earlier, and should give a result of 20% biobased carbon content. Based on this experimental observation and knowing the chemical structure of PET, one can readily calculate and report that the biobased PET has a biobased mass (plant biomass) content of 31.25%. However, there is no direct experimental methodology or protocol that can take a PET bottle or a PE film and conclude that there is biobased content, let alone the amount of biobased content in the product. Biomass content biobased glycol 2 carbon atoms 31.25 by mass There are ongoing efforts to directly calculate and report biomass content; however to-date there is no simple, direct experimental methodology or protocol to do this without going through the biobased carbon content experimental determinations. There is research directed at using CO 2 from smoke stacks and growing algal biomass. Plastics made from this algal biomass will not be able to be identified and quantified using the established radiocarbon test method. While, this may be environmentally beneficial and has value, it is different from the biobased plastics made from plant biomass that photosynthetically fixes CO 2 from the environment and is part of the sustainable, natural biological carbon cycle (as shown in Figure 1). A vast majority of biobased plastics in the market and under development follow this natural biological carbon cycle. The biobased plastics industry needs to be careful to not confuse the marketplace and the general audience by using terms like biomass content or renewable materials or similar terms to describe the current generation of biobased plastics from plant biomass/agricultural crops that remove CO 2 present in the environment through the sustainable, natural biological carbon cycle. [1].Ramani Narayan, Biobased & Biodegradable Polymer Materials-, ACS Symposium Ser. 1114, Chapter 2, pg 13-31, 2012; ACS Symposium Ser. 939, Chapter 18, pg 282, 2006 [2] Ramani Narayan, Carbon footprint of bioplastics using biocarbon content analysis and life cycle assessment, MRS Bulletin, Vol 36 Issue 09, pg. 716 – 721, 2011 bioplastics MAGAZINE [06/13] Vol. 8 53

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