Depth Profiling of a Photochemically Yellowed Paper. Part I: UV-Visible Reflectance and Fluorescence Spectroscopy

Abstract

A strongly photochemically yellowed paper having a reflectance at 457 nm of 53% (initial reflectance 73%) containing high-yield pulp from softwood was ground off to varying depths. The resulting papers were studied with the use of UV-visible diffuse reflectance and fluorescence spectroscopy. Yellowing penetration depth was determined and the chromophore distribution in the z direction was characterized with the aid of difference spectra. Expressed as the amount of chromophores based on the specific adsorption coefficient, 25% of the yellowing had occurred at a depth of 10–12 μm, 50% at 15–20 μm, and 75% at 25–30 μm. The fluorescence spectroscopy results showed that 50% of the changes induced by light had occurred at a depth of about 20 μm.