Effect of Addition of Inorganic Acids or Alkalis on Gelation of Polyvinyl Alcohol Aqueous Solution by γ-Ray Irradiation

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Abstract
Below the critical concentration of polyvinyl alcohol, the effect of inorganic acids or alkalis on gelation of polyvinyl alcohol aqueous solution was investigated by color development with iodine after gamma-ray irradiation. The absorbances of the polyvinyl alcohol-iodine complex decreased remarkably in the presence of nitric or perchloric acid. These acids decompose and form oxygen or hydrogen peroxide which oxidize the polymer and leads to a fading of the color. On addition of sulfuric, phosphoric and hydrochloric acids, the absorbances decrease in the order that agrees with that of the acidity of these acids at the same molarity. In the alkaline solution the absorbances decrease by the addition of sodium hydroxide and aqueous ammonia in the order that agrees with that of the basicity of these alkalis. These results indicate that the gel formation is caused by the radiolysis of water. As a result of chemical analysis, these additives are considered not to be attached to the polymer.

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