By Dr. Ramani Narayan, Consultek
Q 1. Why biobased/renewable materials (bioplastics) and how does using it help sustainable development?
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, environmental responsibility centers on the issue of managing carbon (carbon based materials) in a sustainable and environmentally responsible manner. Natural ecosystems manages 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.
Global Carbon Cycle – Biobased Products Rationale
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. We consume these fossil resources to make our polymers, chemicals & fuel and release the carbon back into the atmosphere as CO2 in a short time frame of 1-10 years (see Figure 1). 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 (>106 years vs. 1-10 years). Thus, we release more CO2 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.
Figure 1. Global carbon cycle – 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 allows 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 towards a net balance between CO2 fixation/sequestration and release due to consumption. Thus, using annually renewable carbon feedstocks allows for:
- Sustainable development of carbon based polymer materials
- Control and even reduce CO2 emissions and help meet global CO2 emissions standards – Kyoto protocol
- Provide for an improved environmental profile
Q 2. How does one define a bioplastic or biobased material?
Based on the discussions above, and the global carbon cycle one defines bioplastic or biboased materials/products or (renewables) as:
Biobased material(s) (ASTM definition also in US Federal Government procurement definition)
Organic material(s) in which the carbon comes from contemporary (new carbon vs old fossil carbon) biological sources
One must define organic materials since the term is used, and for this we adopt the accepted IUPAC (International Union of Pure and Applied Chemistry) nomenclature
Organic material(s) – IUPAC terminology
Material(s) containing carbon based compound(s) in which the carbon is attached to other carbon atom(s), hydrogen, oxygen, or other elements in a chain, ring, or three dimensional structures.
Thus, to be classified biobased, the material must be organic and contain recently fixed (new) carbon present in biological sources
Q 3. How does one quantify biobased or renewable carbon content?
Biobased materials may contain 100% bio-carbon (new carbon) or be mixed (physically, chemically, or biologically) with fossil carbon (old carbon). Therefore, one needs to define biobased content)
Figure 2. Carbon-14 method to identify and quantify biobased content
As shown in Figure 2, 14C signature forms the basis for identifying and quantifying biboased 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 which utilise carbon in biological foodchains take up 14C during their lifetimes. They exist in equilibrium with the 14C concentration of the atmosphere, that is, the numbers of C-14 atoms and nonradioactive 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 14C signature. Thus, by using this methodology one can identify and quantify biobased content. ASTM subcommittee D20.96 developed a test method (D6866) to quantify biobased content using this approach.
D6866 test method involves combusting the test material in the presence of oxygen to produce carbon dioxide (CO2) gas. The gas is analyzed to provide a measure of the products 14C/12C content and relative to the modern carbon-based oxalic acid radiocarbon Standard Reference Material (SRM) 4990c, (referred to as HOxII).
Q 4. How does the radiocarbon method (ASTM D6866) work?
The carbon product is combusted to provide CO2, which is analyzed for the 14C/12C ratio. The 14C/12C ratio is compared directly with an oxalic acid radiocarbon standard reference material (SRM 4990c) that is 100% new (bio) carbon – actually 0.93 of the reference material to correct for the post 1950 14C injection into the atmosphere by nuclear testing.
Three different methods can be used to obtain the 14C/12C ratio, and documented in detail in the Standard – ASTM D6866.
Q. 5. So, how does one obtain and report the biobased or renewable content of the product?
Biobased or renewable content of a product is 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.
Q 6. Why is biobased content on a carbon basis?
This is because the rationale for using biobased products is that one can manage carbon emissions in a
sustainable manner (the rate of carbon fixation by photosynthesis equals the rate of use and liberation to
the atmosphere – carbon neutral). Therefore, it makes sense to use carbon as the basis for the measure of
biboased content and not oxygen or hydrogen or weight or mole. It is sustainable carbon management that
is the driver for biobased products utilization.
Q 7. Given a products elemental composition, how can one compute biobased content theoretically?
Examples of biobased content determination
The following examples illustrate biobased content determinations.
- Product ‘O’ is a fiber reinforced composite with the composition 30% biofiber (cellulose fiber) + 70% PLA (biobased material). The biobased content of Product ‘O’ is 100% — all the carbon in the product comes from biofeedstocks.
- Product ‘P’ is a fiber reinforced composite with the composition 30% glass fiber + 70% PLA (biobased material. The biobased content of Product ‘P’ 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 ‘P’ is 100% but organic content is 70%, implying that the balance 30% is inorganic material. In the earlier example of Product ‘O’ the biobased content is 100% and organic content is 100%. Thus this allows the end-user/customer to clearly differentiate between two 100% biobased products and make their choice on additional criteria – looking at the LCA profile of the two products (using ASTM D 7075).
- Product ‘N’ is a fiber reinforced composite with the composition 30% biofiber (cellulose) + 70% polypropylene (petroleum based organic). Product ‘N’ biobased content = 18.17% and not 30%. Again, biobased content is not based on weight (mass), but on a carbon basis i.e. amount of biobased carbon as fraction weight (mass) or percent weight (mass) of the total organic carbon. Therefore, biobased content = 0.3*44.4 (percent biocarbon; cellulose)/0.7*85.7 (percent carbon in polypropylene)+ 0.3*44.4 (percent biocarbon) * 100 which computes to 18.17%.
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 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 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.
Q 8. Have the theoretical calculations been validated by the ASTM test methods?
The theoretical calculations presented earlier have been validated in experimental observations using ASTM D6866 and are in agreement within +/- 2%.
Q 9. So where does biodegradability fit into this biobased equation?
BIOBASED & BIODEGRADABLE — Single use, short-life, disposable, controlled-life time products like packaging, disposable plastics, agricultural films, marine disposable must be engineered to be biodegradable/compostable, particularly if the disposal infrastructure is composting, anaerobic digestion, waste water treatment, soil, and similar biological infrastructures. In such a case, the product must meet ASTM D6400 Specification standard.
BIOBASED & DURABLE – products like soy polyurethanes for automotive and farm vehicles or Biofiber thermoplastic (like polypropylene) composites for industrial and automotive applications where biodegradability is not a required element for reasons of performance and durability and alternate methods of disposal needs to be designed.
However, one needs to perform LIFE CYCLE ASSESSMENT (LCA) to document positive environmental attributes
- ASTM D7075 “Standard practice for evaluating and reporting environmental
performance of biobased products”. — LCA TOOLS
- To incorporate life cycle costing analysis
References (the above Q & A is excerpted from the following publications)
- 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
- 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
- R Narayan, Proceedings “Plastics From Renewable Resources” GPEC 2005 Global Plastics Environmental Conference – Creating Sustainability for the Environment, February 23-25, 2005
- Proceedings, 1st European BioPlastics Conference Brussels, Belgium Nov. 6 2006
- Presented at SPE National Plastics Exposition (NPE 2006), Bioplastics 101 workshop.
- “Plastics from Renewable Resources an E-live presentation to Society of Plastics Engineers (SPE) 2006
About the Author
|Dr. Ramani Narayan
Professor of Chemical and Biochemical Engineering
Michigan State University
The views, opinions and technical analyses presented here are those of the author, and are not necessarily those of UL, ULProspector.com or Knowledge.ULProspector.com. While the editors of this site make every effort to verify the accuracy of its content, we assume no responsibility for errors made by the author, editorial staff or any other contributor. All content is subject to copyright and may not be reproduced without prior authorization from Prospector.