Mid Sweden University

The light-induced brightness reversion of different types of high-yield pulps has been studied under accelerated and long-term ambient ageing conditions. It was found that accelerated ageing (xenon lamp used as light source) overestimates the yellowing tendencies of hardwood pulps, whereas it was possible to predict the yellowing characteristics of softwood pulps. The lignin content of the pulps was found to be correlated to the degree of photo-yellowing for long-term ambient ageing. A model system was developed which made it possible to study the reflectance/transmittance of thin coating layers and to link this to the inhibition of the light-induced yellowing. The yellowing characteristics of a coated birch CTMP is exemplified using the evolved model system.