A Mechanism for Ultraviolet Light Irradiation - induced Whitening of Poly(vinyl alcohol) Film

Abstract

Poly(vinyl alcohol) (PVA) has been used as a consolidant to prevent flaking of paint pigments on traditional Japanese Shohekiga painted screens and panels. However, over time these PVA coatings can show degradation in the form of loss of transparency due to whitening.

It is believed that this whitening is caused by the scattering of visible light by cracks and wrinkles in the film. These surface defects are thought to be formed by intra- or inter-chain dehydration and chemical cross-linking on the PVA surface.

To validate this conclusion, test PVA films were subjected to quantified UV accelerated aging, because UV exposure is a likely cause of chemical degradation of the PVA layers on Shohekiga.

The test PVA films became white after being irradiated with UV light and then exposed to water vapor. The chemical mechanism was analyzed by spectroscopy and surface observations.