Manufacturers traditionally have not concerned themselves with the impact on the environment of using various feedstocks. They have also not worried about the
"From Conception to
"From Conception to
FIGURE 1.2 Biomass resources: production and utilization.
ultimate disposability of their products. The products of the future must be designed "from conception to reincarnation" or "cradle to cradle" using holistic life-cycle concepts. The use of annually renewable biomass — corn, cellulosics, soy, or other vegetable oils, as opposed to petrochemicals (oil or natural gas) — as the feedstocks for the production of polymers, chemicals, and fuel needs to be understood from a global carbon-cycle basis.
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. To summarize:
Carbon is what we, as well as all of the other plants and animals on earth, are made of; it is 50% of our dry weight. Fossil carbon is in the form of (CH2)n, and biocarbon is in the form of (CH2O)x.
Carbon is of interest because carbon, in the form of carbon dioxide (CO2), is the major greenhouse gas released to the atmosphere as a result of human activities. Excessive levels of greenhouse gases can:
• Raise the temperature of the Earth
• Disrupt the climates that we and our agricultural systems depend on
Concentration of CO2 in the atmosphere has already increased by about 30% since the start of the Industrial Revolution.
Most of the increase in atmospheric CO2 concentrations has come from and will continue to come from the use of fossil fuels (coal, oil, and natural gas) for energy.
Much (20 to 25%) of the increase over the last 150 years has come from changes in land use, e.g., the clearing of forests and the cultivation of soils for food production.
Therefore, discussions on sustainability, sustainable development, and environmental responsibility center on the issue of managing carbon-based materials in a sustainable and environmentally responsible manner. Natural ecosystems manage carbon through the 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 CO2. Photoautotrophs like plants, algae, and some bacteria fix this inorganic carbon to organic carbon (carbohydrates) using sunlight for energy:
Over geological time frames (>106 years), this organic matter (plant materials) is fossilized to provide our petroleum, natural gas, and coal. Clearly, petrochemical feedstocks are therefore also "natural." We consume these fossil resources to make our polymers, chemicals, and fuel, thereby releasing the carbon back into the atmosphere as CO2 within a short time frame of 1 to 10 years (see Figure 1.3). Thus, the rate at which biomass is converted to fossil resources is in total imbalance with the rate at which they are consumed and liberated (>106 years vs. 1 to 10 years). The release of more CO2 than we sequester as fossil resources creates a kinetics problem. Clearly, this is not sustainable, and we are not managing carbon in a sustainable and environmentally responsible manner.
Polymers, chemicals and fuels
CO2 and biomass
FIGURE 1.3 Global carbon cycling: sustainability driver.
FIGURE 1.3 Global carbon cycling: sustainability driver.
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 CO2 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 CO2 rate equation and move toward a net balance between CO2 fixation/sequestration and release due to consumption.
Thus, using annually renewable biomass feedstocks to manufacture carbon-based materials and products allows for:
• Sustainable development of carbon-based polymer materials and products
• Control and even reduction of CO2 emissions, thus helping to meet the global CO2 emissions standards established by the Kyoto Protocol
• An improved environmental profile
1.2.2 Standards for Biobased Materials/Products
Implementing the use of biobased products requires that the following questions be addressed to prevent confusion and misrepresentation in the marketplace:
• How do you differentiate between biobased (renewable) and nonbiobased materials, i.e., fossil, inorganics?
• How do you define and quantify biobased content? This is an important issue, since most products would continue to have some fossil carbon content to obtain adequate performance and cost benefits.
• How do you evaluate and report on the environmental profile/footprint?
• Quantitatively show improved environmental profile of biobased products
• Demonstrate cost and performance benefits
To address these questions, ASTM (American Society for Testing and Materials) International Committee D20.96  developed standards for identifying and quantifying biobased materials and products.
Based on earlier discussions and Equation 1.1, one defines biobased and organic materials as follows:
Biobased materials: organic materials in which the carbon comes from contemporary (nonfossil) biological sources Organic materials: materials containing carbon-based compounds in which the carbon is attached to other carbon atoms, hydrogen, oxygen, or other elements in a chain, ring, or three-dimensional structure (IUPAC [International Union of Pure and Applied Chemistry] nomenclature)
Therefore, to be classified as biobased, the materials must be organic and contain recently fixed (new) carbon from biological sources. A 100% biobased material
CO2 Solar radiation
C signature forms the basis to identify and quantify biobased content--ASTMD6366
Fossil feedstocks—Petroleum, Natural gas, Coal
FIGURE 1.4 Carbon-14 method to identify and quantify biobased content.
would be an ideal scenario, but realistically, in practice, most products would contain some nonbiobased materials (inorganic fillers, fossil-based materials) to satisfy performance and cost requirements. Therefore, quantifying the biobased content of a material/product is of paramount importance. ASTM has developed an elegant and absolute method to identify and determine the biobased content of biobased materials using carbon-14 radioactive signatures associated with biocarbon.
As shown in Figure 1.4, the 14C signature forms the basis for identifying and quantifying biobased content. The CO2 in the atmosphere is in equilibrium with radioactive 14CO2. Radioactive carbon is formed in the upper atmosphere through the effect of cosmic-ray neutrons on 14N. It is rapidly oxidized to radioactive 14CO2 and enters the Earth's plant and animal lifeways through photosynthesis and the food chain. Plants and animals that utilize carbon in biological food chains take up 14C during their lifetimes. They exist in equilibrium with the 14C concentration of the atmosphere, that is, the numbers of 14C atoms and nonradioactive carbon atoms stay approximately the same over time. As soon as a plant or animal dies, it ceases 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 14C signature. Thus, by using this methodology, one can identify and quantify biobased content. ASTM Subcommittee D20.96 developed a test method (D 6866) to quantify biobased content using this approach .
Test method D 6866 involves combusting the test material in the presence of oxygen to produce CO2 gas. The gas is analyzed to provide a measure of the products. The 14C/12C content is determined relative to the modern carbon-based oxalic acid radiocarbon standard reference material (SRM) 4990c, referred to as HOxII. Three different methods can be used for the analysis. The methods are:
• Test method A utilizes liquid scintillation counting (LSC) radiocarbon (14C) techniques by collecting the CO2 in a suitable absorbing solution to quantify the biobased content. The method has an error of 5 to 10%, depending on the LSC equipment used.
• Test method B utilizes accelerator mass spectrometry (AMS) and isotope ratio mass spectrometry (IRMS) techniques to quantify the biobased content of a given product with possible uncertainties of 1 to 2% and 0.1 to
0.5%, respectively. Sample preparation methods are identical to method A except that, in place of LSC analysis, the sample CO2 remains within the vacuum manifold and is distilled, quantified in a calibrated volume, and transferred to a torch-sealed quartz tube. The stored CO2 is then delivered to an AMS facility for final processing and analysis.
• Test method C uses LSC techniques to quantify the biobased content of a product. However, whereas method A uses LSC analysis of CO2 cocktails, method C uses LSC analysis of sample carbon that has been converted to benzene. This method determines the biobased content of a sample with a maximum total error of ±2% (absolute).
Although test methods A and C are less sensitive than that of method B, using AMS/IRMS, they have two distinct advantages:
• Lower costs per evaluation
• Much greater instrument availability worldwide
The nuclear testing programs of the 1950s resulted in a considerable enrichment of 14C in the atmosphere. Although it continues to decrease by a small amount each year, the current 14C activity in the atmosphere has not reached the pre-1950 level. Because all 14C sample activities are referenced to a "prebomb" standard, and because nearly all new biobased products are produced in a postbomb environment, all values (after correction for isotopic fractionation) must be multiplied by 0.93 (as of the writing of this standard) to better reflect the true biobased content of the sample.
Thus, the biobased content of a material is based on the amount of biobased carbon present and is defined as follows:
Biobased content or gross biobased content: the amount of biobased carbon in the material or product as fraction weight (mass) or percent weight (mass) of the total organic carbon in the material or product (ASTM D 6866).
1.2.3 Examples of Biobased Content Calculations
The following examples illustrate biobased content determinations on a theoretical basis.
Let us say that a fiber-reinforced composite with the composition 30% biofiber (cellulose fiber) + 70% PLA (poly[lactic acid], a biobased material) is formulated. The biobased content of this composition would be 100% since all of the carbon is biocarbon.
If the fiber-reinforced composite is formulated with the composition 30% glass fiber (inorganic material) + 70% PLA (biobased material), the biobased content is still 100%, and not 70%. This is because the biobased content is on the basis of carbon, and glass fiber has no carbon associated with it; therefore, all carbon in this product is biocarbon. This would be the case if one were to formulate a product with water or other inorganic fillers. As discussed in previous 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 as the basis for determining biobased content. It is also fortuitous that an absolute method using 14C is available to measure the biobased carbon present in a material. Clearly, there may be positive or negative environmental impacts on the use of the noncarbon materials, and this needs to be addressed separately. In any case, one must define biobased content and organic content. Thus, the biobased content of the glass-fiber-reinforced composite is 100%, but the organic content is 70%, implying that the balance 30% is inorganic material. In the earlier example, the biobased content is 100% and the organic content is 100%. This distinction allows end-users/customers to clearly differentiate between two 100% biobased products and make their choice on additional criteria, e.g., by looking at the LCA (life-cycle assessment) profile of the two products (using ASTM D 7075).
As another example, let us say that a fiber-reinforced composite with the composition 30% biofiber (cellulose) + 70% polypropylene (petroleum-based organic) is formulated. The biobased content of this formulation is 18.17% and not 30%. Again, biobased content is based not on weight (mass), but on a carbon basis, i.e., the amount of biobased carbon as fraction weight (mass) or percent weight (mass) of the total organic carbon. Therefore, the biobased content for this product is
0.3 X 44.4 (percent biocarbon in cellulose)
0.7 X 85.7 (percent carbon in polypropylene) + 0.3 X 44.4 (percent total biocarbon)
which computes to 18.17%.
The theoretical calculations presented here have been validated in experimental observations using ASTM D 6866 and are in agreement within ±2%.
The U.S. Congress passed the Farm Security and Rural Investment Act of 2002 (P.O. 107-171), requiring the purchase of biobased products by the federal government. The U.S. Department of Agriculture (USDA) was charged with developing guidelines for designating biobased products and publishing a list of designated biobased product classes for mandated federal purchase . In its rule making, the USDA adopted the previously described methodology for identifying and quantifying biobased content and required the use of ASTM D 6866 to establish biobased content of products.
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