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Special Polymers May Staunch Radioactive Leak

Special Polymers May Staunch Radioactive Leak

Japanese engineers stuffed sawdust, three garbage bags of shredded newspaper and superabsorbent polymer (SAP) into an eight-inch reactor containment crack in a desperate bid to stop radioactive water from leaking into the Pacific Ocean.

An earlier effort to fill the hole with concrete failed.

"We will continue to take all measures to ensure the safety and to continue monitoring the surrounding environment around the Power Station," the Tokyo Electric Power Co. said in an official statement regarding conditions at the Fukushima Daiichi Nuclear Power Station, which suffered the double whammy of an earthquake and a tsunami on March 11.

News reports indicated that the polymer mix was not initially successful and that workers were stirring the mix in order to activate the polymers.

Design News could not ascertain the supplier of the polymer or the specific formulation last night.

That information is critical because superabsorbent polymers are highly engineered to perform specific tasks. It seems logical that the polymers came from a Japanese source, however, since there are major chemical companies there that manufacture SAPs.

They were first developed in the 1960s by the U.S. Department of Agriculture. Their basic chemistry is fascinating.

The USDA was researching materials that could improve water conservation in soils. USDA scientists designed a resin based on the grafting of acrylonitrile polymer onto the backbone of starch molecules. The hydrolyzed product produced water absorption greater than 400 times its weight. Conventional natural materials such as cotton and sponges can only absorb up to 20 times their weight.

Japanese companies began independent research to develop their own technology, and focused on use of starch, carboxy methyl cellulose (CMC), acrylic acid, polyvinyl alcohol (PVA) and isobutylene maleic anhydride (IMA).

Early Japanese researchers worked at Sanyo Chemical, Sumitomo Chemical, Kao, Nihon Starch and Japan Exlan. Other global players included Dow Chemical, Hercules, General Mills Chemical, DuPont, National Starch & Chemical and Enka (Akzo), according to a history by M2 Polymer Technologies Inc.

Special Polymers May Staunch Radioactive Leak
According to an engineering web site at the University of Buffalo, these Japanese companies produce SAPs: Nippon Shokubai, Sanyo, Mitsubishi Petrochemical Company and Sumitomo Seika.

Superabsorbent diapers were introduced in Japan in 1983, and are now widely used in plastic diapers globally. Ultra Pampers by Procter & Gamble were the first diaper introduced in the United states to use superabsorbent polymers.

The absorbency of the polymer in diapers is carefully engineered to match the projected output of urine from a baby. SAPs designed for maximum absorption can create gel blocks that prevent all of the urine from reaching the diaper. Also, if the absorption rate of the diaper is slower than the urination rate of the baby, leakage will occur.

Now SAPs are engineered for other tasks, such as solidifying waste waters and sludge.

Waste Lock 770 from M2 Polymer Technologies has been engineered to absorb under pressure and has properties that make it ideally suited for the absorption and solidification of low-level radioactive waste and other types of waste sludges. It's approved for use at the nuclear production site in Hanford, WA.

Conventional industrial absorbents include lime kiln dust, Portland cement, dried corn cob, shredded newspaper, bentonite clay and saw dust.

"In the case of radioactive waste, where loads must be shipped long distances and landfill costs can reach $1000 per cubic yard or more, the use of super absorbent polymer to prevent volume expansion is quickly realized in cost saving," said Martin Matushek, vice president of M2 Polymer Technologies of West Dundee, IL, in an article published in 2007.

Waste Lock polymers are based on polycarboxylate chemistry that provides a strong ion exchange affinity for soluble metal ions.
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