Ultraviolet-induced crosslinking of poly(vinyl alcohol) in the presence of sensitizers

Abstract

Ultraviolet-induced crosslinking of the film of polyvinyl alcohol with different degrees of polymerization was investigated in air at 25°C. in the presence of sodium benzoate as a sensitizer. Crosslinking is always accompanied by photolysis of the sensitizer. In the absence of the sensitizer, no crosslinking occurred. The gel content increased with irradiation time, and tended to a limiting value, depending on the initial sensitizer concentration. The final gel content increased as a function of the initial amount of sodium benzoate. A plot of solubility (S + S1/2) against the reciprocal of the concentration of sensitizer converted gives a straight line in each case. The number of crosslinks is directly related to the number of sensitizer molecules destroyed. The crosslinking occurred predominantly, and main-chain scission was negligible. This result is in marked contrast to the effect of ionizing radiation, since the ionizing radiation causes only degradation under the identical conditions. This ultraviolet method was applied successfully to the crosslinking of water-soluble cellulose derivatives, such as methyl cellulose and sodium carboxymethyl cellulose.