Basics How much
Basics How much “biocontent” is in there? A scientifically proper calculation of the biobased content is more complex than one thinks... Biobased and biodegradable plastics can form the basis for an environmentally preferable, sustainable alternative to petroleum based plastics. These biobased materials offer value in the sustainability/life-cycle equation by being part of the biological carbon cycle, especially as it relates to carbon-based polymeric materials such as plastics for example. However, not all “so-called” bioplastics materials currently available are 100% biobased. There are for example blends of plastics made of renewable resources with those made of fossil oil or composites with different kind of fibers. But it would be too simple – or better incorrect – to say that a blend of 30 grams of a material made of renewable resources and 70 grams of a fossil based plastic would be 30% biobased. Global Carbon Cycle – Biobased Products Rationale Carbon is the major basic element that is the building block of polymeric materials -- biobased products, petroleum based products, biotechnology products, fuels, even life itself. Therefore, discussions on sustainability, sustainable development, and environmental responsibility centers on the issue of managing carbon (carbon based materials) in a sustainable and environmentally responsible manner. Natural ecosystems manage carbon through its biological carbon cycle, and so it makes sense to review how carbon based polymeric materials fit into nature’s carbon cycle and address any issues that may arise. Carbon is present in the atmosphere as CO 2 . Plants, for example fix this inorganic carbon to organic carbon (carbohydrates) using sunlight for energy. CO 2 + H 2 O + sunlight energy -> (CH 2 O) x + O 2 Over geological time frames (>10 6 years) this organic matter (plant materials) is fossilized to provide our petroleum, natural gas and coal. We consume these fossil resources to make our polymers, chemicals and fuel and release the carbon back into the atmosphere as CO 2 in a short time frame of 1-10 years. However, the rate at which biomass is converted to fossil resources is in total imbalance with the rate at which they are consumed and liberated (> 10 6 years vs. 1-10 years). Thus, we release more CO 2 than we sequester as fossil resources – a kinetics problem. Clearly, this is not sustainable, and we are not managing carbon in a sustainable and environmentally responsible manner. However, if we use annually renewable crops or biomass as the feedstocks for manufacturing our carbon based polymers, chemicals, and fuels, the rate at which CO 2 is fixed equals the rate at which it is consumed and liberated – this is sustainable and the use of annually renewable crops/biomass would allow us to manage carbon in a sustainable manner. Furthermore, if we manage our biomass resources effectively by making sure that we plant more biomass (trees, crops) than we utilize, we can begin to start reversing the CO 2 rate equation and move towards a net balance between CO 2 fixation/sequestration and release due to consumption. “New” and “old” carbon Based on the above discussion, one can define biobased materials as follows: Biobased Materials – organic materials in which the carbon comes from contemporary (non-fossil) biological sources - “new carbon” Organic Materials – materials containing carbon based compounds in which the carbon is attached to other carbon atoms, hydrogen, oxygen, or other elements Therefore, to be classified as biobased, the materials must be organic and contain recently fixed “new carbon” from biological sources. Of course, organic materials from fossil (petroleum, coal, natural gas) resources contain “old (fossil) carbon” The question then arises: • How does one distinguish between “new” (contemporary) and “old” (fossil) carbon – i.e. identify biobased carbon? • How does one quantify biobased carbon content? Here, the so called radiocarbon method can help. Basically carbon exists in form of three different isotopes: 12 C, 13 C (which shall be neglected here) and 14 C. In the atmosphere the 12 C carbon in CO 2 is in equilibrium with 14 C carbon. Therefore, 36 bioplastics MAGAZINE [01/07] Vol. 2
Basics Global carbon cycle photosynthesis CO 2 biomass/ Bio-organic 1 - 10 years Bio-chemical industry > 10 6 years Polymers, Chemicals & & Fuels chemical industry Fossil Recourses (Petroleum, Coal, Natural gas) carbon entering the earth‘s plant and animal lifeways through photosynthesis contains radioactive 14 C. Since the half life of 14 C carbon is around 5730 years, the fossil feedstocks which form over millions of years will have no 14 C but only 12 C - “old carbon”. Thus, by using this methodology one can identify and quantify biocarbon (biobased) content. ASTM D6866 describes a test method to quantify biocontent (biobased) content using this approach. Biobased content of material It, therefore, follows that the biobased content of a material is based on the amount of biobased carbon (which contains 14 C) present, and defined as follows: Biobased content or gross biobased content is the amount of biobased carbon in the material or product as a fraction weight (mass) or percent weight (mass) of the total organic carbon in the material or product (ASTM D6866). Biobased Products are products made by transforming (chemically, biologically or physically blending) biobased materials, either exclusively or in combination with non-biobased materials. Some examples shall illustrate the determination of the biobased content: Product A is a fiber reinforced composite consisting of 30% biofiber (cellulose fiber) and 70% PLA (biobased material). The biobased content of this Product A is 100% - all the carbon in the product comes from bio-resources. Product B is a fiber reinforced composite consisting of 30% glass fiber and 70% PLA (biobased material). The biobased content of this Product B is 100%, not 70%. This is because the biobased content is on the basis of carbon, and glass fiber has no carbon associated with it. However, in all cases, one must define biobased content and organic content. Thus, the biobased content of Product B is 100% but organic content is 70% because the 30% of glass is inorganic. Product C is a fiber reinforced composite consisting of 30% biofiber (cellulose) and 70% polypropylene (petroleum based organic). Product C biobased content is 18.17% and not 30%. Here the cellulose fibers consist of 44.4% biocarbon ( 14 C) and the Polypropylene consists of 85.7% of fossil based ( 12 C) carbon. So the equation is 0.3 * 0.444 ______________________ = 0.1817 = 18.17% 0.3 * 0.444 + 0.7 * 0.857 The justification and rationale for using carbon and not the weight or moles or other elements like oxygen, or hydrogen as the basis for establishing bio (biobased) content of products should now be very self evident. As discussed in earlier sections, the rationale for using biobased products is to manage carbon in a sustainable and efficient manner as part of the natural carbon cycle, therefore it makes sense to use carbon ( 14 C vs. 12 C) as the basis for determining biobased content. Acknowledgements: This article is based on a paper by Prof. Ramani Narayan (narayan@msu.edu), presented at the National American Chemical Society, Division of Polymer Chemistry meeting, San Diego (2005); ACS Symposium Ser (An American Chemical Society Publication), 939 June 2006 bioplastics MAGAZINE [01/07] Vol. 2 37
