Ultraviolet degradation of poly(vinyl alcohol) used in restoration of historical and cultural properties

Six types of poly(vinyl alcohol) were degraded by ultraviolet irradiation with wavelengths of 185, 254, and 365 nm, respectively. The degradation fragments were characterized by attenuated total reflectance Fourier transform infrared (ATR-FT/IR), gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) including two-dimensional (2D) NMR measurements. Absorption peaks assigned to C-O at 1020, 1090, 1180, and 1250 cm−1 were observed in ATR-FT/IR spectra, and molecular weights decreased from 9 × 104 to about 7 × 104 in GPC measurements. In addition, spectra of proton and carbon NMR including 2D-NMR were clearly measured and analyzed after ultraviolet irradiation of PVA films from both front and back sides. Based on these results, the degradation mechanism is discussed and concluded.