Nearly 20 years ago the experts at EPI developed materials TDPATM and processes for controlling the lifetime of conventional polyethylene and polystyrene resin. The plastic products made using conventional resins to which EPI's TDPATM has been added to retain all the advantages of the conventional products but display the required additional characteristic of degrading rapidly after use and disposal, by natural mechanisms and with no unwanted environmental consequences. There is a simple explanation as to how this works.
It has been known for some time that hydrocarbons such as polyolefins degrade slowly by a process called oxidative degradation -- a sequence of free-radical reactions whereby atmospheric oxygen combines with the carbon and hydrogen in the plastic molecules, with a number of inevitable consequences:
Although polyolefins do not biodegrade because their molecules are too large and are hydrophobic, their much smaller hydrophilic oxidation products do. Over a period of many years, ordinary polyolefins can undergo this two-stage process -- oxidation followed by the biodegradation of the oxidation products. This is analogous to the slow bioassimilation of naturally-occurring materials, for example polymers such as leaves, straw and natural rubber.
While the slow oxidation / biodegradation of the polyolefins is understood to be useful in the long term, it is necessary to speed up this two-stage process drastically in order to make it practically useful in managing the accumulation of discarded plastic products. It is essential, however, to retain all the useful properties of polyolefins while adding the characteristic of rapid oxidation followed by biodegradation -- but not until the useful life of the plastic is over. For example, polyolefins are hydrophobic and therefore not biodegradable. This is important in keeping food from spoiling in plastics bags or food wrap while transporting and displaying perishable food items. Furthermore, while it is relatively easy to make the polyolefins degrade more rapidly than normal, this is not what is required. Processability, shelf life and use life must be maintained. Rapid degradation must not begin until the material has been used, possibly several times, then finally discarded. The shelf life and service life could be as short as a few months or as long as several years.
The controlled lifetime technology developed by EPI for polyolefins works in the following way: Proprietary TDPATM formulations contain fatty acid compounds of specific transition metals (iron is an example of a transition metal) as their primary active ingredient. They act as catalysts in speeding up the normal reactions of oxidative degradation with the overall process increased by up to several orders of magnitude (factors of 10). (It should be noted that catalysts of many kinds are widespread in Nature; others are used very commonly by industry. By definition, it takes only a small amount of catalyst to do what is required and the catalyst is not consumed in the reaction). The products of the catalyzed oxidative degradation of the polyolefins are precisely the same as for conventional polyolefins because, other than a small amount of TDPATM present, the plastics are conventional polyolefins. Many commercially useful hydrocarbons (e.g., cooking oils, polyolefins, many other plastics) contain small amounts of additives called antioxidants that prevent oxidative degradation during storage and use. Antioxidants function by 'deactivating' the free radicals that cause degradation. Lifetime (shelf life + use life) is controlled by antioxidant level and the rate of degradation after disposal is controlled by the amount and nature of the TDPATM catalyst. The latter is the EPI product in the form of a fine dispersion in a polymeric matrix to be added by the converter to conventional polyolefin resin at a level recommended by EPI (generally in the range of 2 -10%) depending on the specific applications and the performance required.
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