Photo-degradation of PADC by UV radiation at various wavelengths

Abstract

The effects of ultraviolet (UV) photons at different wavelengths (namely UVA, UVA + B and UVC) on PADC (polyallyl diglycol carbonate) were investigated in this study. The chemical modifications were studied by Fourier Transform Infrared (FTIR) spectrometry and the corresponding nano-mechanical properties were also determined. The scission process could be revealed by the decreasing net absorbance at particular wavelengths in the infrared (IR) spectra. On the other hand, the cross-linking was indicated by the increased hardness and reduced modulus determined with a nanoindenter. UVA caused no chemical modifications as most of the UV photons in this range were not absorbed by PADC. Both UVA + B and UVC irradiation caused scission of the chemical bonds, which was also manifested by the faster chemical etching rates. The bulk etch rate increased from 1.37 to 5.73 μm/h for 60 h of UVA + B exposure for 3 h of chemical etching, and increased to 5.13 μm/h for 60 h of UVC exposure. For 3 h of etching, the bulk etch rate remained unchanged for UVC exposures longer than 20 h. The saturation of the bulk etch rate was due to formation of cross-linked structures on the surface of the PADC samples. It was also observed that a UVC exposure caused a comparatively higher bulk etch rate at the beginning of etching. However, the bulk etch rate decreased with the depth of the PADC sample due to the lower rate of oxygen diffusion into deeper regions.