Brightness Reversion of Mechanical Pulps. Part XVII: Diffuse Reflectance Study on Brightness Stabilization by Additives Under Various Atmospheres

Abstract

Brightness reversion of softwood (SW) and hardwood (HW) bleached chemithermomechanical pulps (BCTMP) with a 300–400 nm light source under argon, oxygen, and air were studied in the absence and presence of UV-screens using UV–Vis reflectance difference spectroscopy. The UV-Vis difference absorption spectra of control SW and HW BCTMP testsheets indicate that as the concentration of atmospheric oxygen is increased, the absorption at λmax ≈ 360 nm increases and a blue shift occurs. In all of the cases studied, brightness reversion was observed to occur under an argon atmosphere. The addition of benzophenone and benzotriazole additives to BCTMP testsheets resulted in a significant decrease in formation of chromophores absorbed at ∼ 400 nm and ∼ 360 nm. The possible mechanisms contributing to these effects are discussed in terms of the photoformation of lignin chromophoric structures.