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The Effect of Ultraviolet Irradiation on Photooxidation and Crosslinking Reactions in a Poly(Vinyl Alcohol)- Ammonium Dichromate System

The chemical transformation of poly(vinyl alcohol) (PVA) film by ammonium dichromate on exposure to ultraviolet irradiation have been investigated. The oxidative transformation was followed spectrophotometrically and the extent of crosslinking reaction by measuring the solubility and the viscosity changes of the exposed film. The influence of the time of exposure as well as the concentration of ammonium dichromate on the above reactions has been established. The ultraviolet and infrared data of exposed film showed that hydroxyl groups are oxidized to carbonyl groups. Absorption bands at 230, 270 and 330 mm, attributed to the presence of the double bond conjugated with carbonyl, were increased during the exposed period. The bromination and hydrogenation of the dissolved films decreased those absorptions. This indicated that the content of the carbonyl groups and double bonds were increased during the irradiation. The partial insolubilization of the exposed film was attributed to the formation of complexes of alcohol and carbonyl groups to chromic ions formed by reduction of the dichromate.

poly(vinyl alcohol); ammonium dichromate; irradiation; crosslinking; viscosity

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