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How Oxo-biodegradable Plastics Work...a simple explanation of a complex technology!
Industrial ecology is the controlling of the life cycle of manufactured goods. It represents a significant challenge in today's marketplace. PLastics Solutions, working with partners, uses a proprietary technology in two of its products that will degrade common plastics in a controlled, ecologically responsible manner.
Every combination of elements has a gram molecular weight. The water molecule, H2O, has a gram molecular weight of 18. Carbon Dioxide, CO2, has a gram molecular weight of 44. An ordinary polyethylene film molecule has a gram molecular weight of around 300,000.
The remarkable flexibility, stretchability and toughness of polyethylene film arise from the size of the molecule from which it is made. Many of the uses of this tough plastic product require it to perform its intended function for a relatively short period of time and then degrade or decompose more rapidly than normal in specific disposal environments. All this must occur in ways that are entirely environmentally benign, there must be no environmental damage. Such products will be "controlled lifetime" plastics".
The proprietary additive Plastics Solutions uses, when added to the manufacture of common plastics, will cause the plastic to photo, thermal and chemically degrade as litter in anaerobic landfills and aerobic compost facilities. These plastics will progressively degrade to lower and lower molecular weights, discolor, become brittle, fragment, until a point in time when they are digested by the micro-organisms back to the basic elements of carbon dioxide, water and the biomass that is the natural product of the bio-cycle. There are no harmful residues.
This unique additive produces controlled lifetime plastics, and this is the story of why and how they work. Heat, UV light and mechanical stress are the most common ways in which oxidative degradation is triggered. One, or any combination of the above factors is needed to start the degradation process. Once the process has started it will not stop.
The long polyethylene molecule with its average molecular weight of 300,000 is first broken into smaller molecules, for example 100,000 each. Microorganisms still have not developed enzymes, which can digest these molecules. The continuation of the reduction of molecular weight by oxidative degradation results in the formation of many more molecule ends, reaching a point at which certain types of microbes begin chopping off 2 carbon atom fragments from these ends. As the average molecular weight decreases, causing more and more ends, the attack of the microorganisms increases. Eventually as oxidative degradation and biodegradation proceed, more and more hydrogen and some of the carbon (both from the polyethylene) are converted to water and carbon dioxide, respectively. Long before the fragments of the initial molecules become water-soluble, biodegradation takes over, and the result is biodegradation.
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This line represents a polyethylene molecule with an average molecular weight (AMW) of 300,000.
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This line represents fragments of the above molecule after some oxidative degradation.
(AMW 100,000)
_____ _____ ______ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
This shorter line represents even smaller fragments (AMW 30,000) of the original polyethylene molecule after further oxidative degradation.
Although they are still much too large to be water soluble, they are biodegradable. Common microorganisms convert these fragments to carbon dioxide, water and biomass. This, of course, is part of the natural bio-cycle.
It must be emphasized that a piece of polyethylene the size of this page consists of millions upon millions of polyethylene molecules. Each of them is subject to the same oxidative degradation and subsequent biodegradation as shown schematically above for a single molecule. It should be noted that these types of chemistry proceed regardless of the size of the piece of plastic or the number of molecules.
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