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bioplasticsMAGAZINE_0901

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bioplasticsMAGAZINE_0901

Politics

Politics Biodegradability... Article contributed by Ramani Narayan University Distinguished Professor Department of Chemical Engineering & Materials Science Michigan State University, East Lansing, MI, USA Biodegradability is an end-of-life option that allows one to harness the power of microorganisms present in the selected disposal environment to completely remove plastic products designed for biodegradability from the environmental compartment via the microbial food chain in a timely, safe, and efficacious manner. Because it is an end-of-life option, and harnesses microorganisms present in the selected disposal environment, one must clearly identify the ‘disposal environment’ when discussing or reporting on the biodegradability of a product – like biodegradability under composting conditions (compostable plastic), under soil conditions, under anaerobic conditions (anaerobic digestors, landfills), or under marine conditions. Specifying time to complete biodegradation or put in a better way time to complete microbial assimilation of the test plastic in the selected disposal environment is an essential requirement – so stating that it will eventually biodegrade or it is partially biodegradable or it is degradable is not acceptable. High school or college biology/biochemistry teaches that microorganisms utilize/consume carbon substrates by transporting the material inside its cell, oxidizing the carbon to CO 2 , which releases energy that it harnesses for its life processes (discussed in more detail later in the paper). So a measure of the evolved CO 2 is a direct measure of the ability of the microorganisms present in that disposal environment to utilize the carbon plastic product. Unfortunately, there is a growing number of misleading, deceptive, and scientifically unsubstantiated biodegradability claims proliferating in the marketplace. This is causing confusion and skepticism among consumers, end-users, and other concerned stakeholders – in turn this is bound to hurt not only the fledgling bioplastics industry, but the plastics industry as a whole. Some examples of manufacturer’s product claims are shown below – the direct quotes from the manufacturer’s web site or product brochure are shown in italics. Biodegradable PVC product claim “Biodegradation process begins only when the bio PVC film is introduced into an environment (compost, both commercial and home, trash dump, the ground, lakes, rivers and the ocean) that allows microorganisms, which break down matter, to come into constant contact with the bio PVC film. Once that happens the ‘special ingredients’ attract the microorganisms that begin to break the hydrogen carbon chain that exists in the PVC. Once the chain is broken, this allows oxygen to enter which will attach itself to the hydrogen and carbon creating H 2 O and CO 2 . The lone chlorine atom bonds to a hydrogen atom creating a very weak salt that does not have any adverse effect on the ecosystem. The biodegradation process works in both aerobic and anaerobic conditions. So the absence of oxygen or water will not keep the bio PVC film from biodegrading. All that is needed are the microorganisms” There is no scientific data provided to substantiate the complete breakdown and utilization of the PVC by the microorganisms present in the disposal system resulting in CO 2 and water as claimed. Furthermore, the proposed mechanistic chemistry describing the process would not pass muster in a high school honors chemistry classroom. However, a major corporation has adopted the biodegradable PVC card as an environmentally responsible ‘green’ solution because it is claimed to be ‘biodegradable’. Biodegradable PET product claim “By having a more earth friendly PET biodegradable container and becoming a partner in helping to develop effective recycling programs, we can stem the rising tide of plastic pollution and leave our world a better place for future generations. Our bottles are 100% biodegradable in anaerobic (no oxygen, no light), aerobic and compostable environments and can be intermingled with standard PET during recycling. Our patented pending process allows our bottles to be metabolized and neutralized in the environment, turning them into inert humus (biomass), biogas (anaerobic) or CO 2 (aerobic)” Again, no scientific data showing the 100% carbon conversion to biogas in an anaerobic environment or CO 2 in an aerobic environment using well established standard test methods in literature whether from the OECD, ISO, ASTM, or EN was presented. 28 bioplastics MAGAZINE [01/09] Vol. 4

Politics Sorting through Facts and Claims Oxo-biodegradable polyethylene (PE) film claims ”The technology is based on a very small amount of prodegradant additive being introduced into the manufacturing process, thereby changing the behavior of the plastic and the rate at which it degrades. The plastic does not just fragment, but is then consumed by bacteria and fungi and therefore continues to degrade to nothing more than carbon dioxide, water and biomass with no toxic or harmful residues to soil, plants or macro-organisms”. “Designed to interact with the microorganisms present in landfills, composters, and almost everywhere in nature including oceans, lakes, and forests. These microorganism metabolize the molecular structure of the plastic breaking it down into soil”. “Combined with an oxo-biodegradable proprietary application method to produce films for bags. This product, when discarded in soil in the presence of microorganisms, moisture, and oxygen, biodegrades, decomposing into simple materials found in nature. Completely breakdown in a landfill environment in 12-24 months leaving no residue or harmful toxins and have a shelf life of 2 years”. In each of the above cases no scientific data showing carbon conversion to CO 2 using established standard test methods is documented. Another company claims a biodegradable plastic based on an additive technology different from the oxo-degradable additive class. Their claims reads “Plastic products with our additives at 1% levels will fully biodegrade in 9 months to 5 years wherever they are disposed like composting, or landfills under both aerobic and anaerobic conditions”. However, the graph of percent biodegradation against time in days shows the biodegradation curve reaching a plateau around 20% using a 50% additive master batch. In the final film samples, the recommended level of additive is only 1%. So the observed 20% would be even lower. However, the claim is made that “the results of the aerobic biodegradation tests, indicate, that in time, plastics produced using the 1% additive will fully biodegrade.” There are many more such examples of misleading claims. Several offer weight loss and other chemical evidence for the break down of the polymer into fragments. However, little or no evidence is offered that these fragments are completely consumed by the microorganisms present in the disposal environment in a reasonable defined time period. In a few cases evidence presented shows partial biodegradation, after which the biodegradation curve plateaus. However, if one obtains only 5% or 30% or even 40% biodegradation, there is serious health and environmental consequences caused by the non-degraded fragments as it moves through eco compartments as discussed later. Fundamental Principles in Biodegradable Plastics Microorganisms (billions of them per gram of soil) are present in the environment. Figure 1 shows a low temperature electron micrograph of a cluster of E. Coli bacteria. Designing plastics and products to be completely consumed (as food) by such microorganisms present in the disposal environment in a short time frame is a safe and environmentally responsible approach for the end-oflife of these single use, short-life disposable packaging and consumer articles. The key phrase is ‘complete ‘ – if they are not completely utilized, then these degraded fragments, which may even be invisible to the naked eye, pose serious environmental consequences. Microorganisms utilize the carbon product to extract chemical energy for their life processes. They do so by: 1. breaking the material (carbohydrates, carbon product) into small molecules by secreting enzymes or the environment (temperature, humidity, sunlight) does it. 2. Transporting the small molecules inside the microorganisms cell. 3. Oxidizing the small molecules (again inside the cell) to CO 2 and water, and releasing energy that is utilized by the microorganisms for its life processes in a complex biochemical process involving participation of three metabolically interrelated processes (tricarboxylic acid cycle, electron transport, and oxidative phosphorylation). Figure 1 (Source: http://emu.arsusda.gov/) bioplastics MAGAZINE [01/09] Vol. 4 29

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