Photoyellowing of mechanical pulps - III. Intensity effects and dose-response relationships

The increase in yellowness index of mechanical pulp (newsprint) paper on exposure to monochromatic radiation at several discrete wavelengths in the region of 260 to 600 nm was studied. As already reported the effectiveness of yellowing was shown to decrease logarithmically with increasing wavelength. The effectiveness of yellowing at constant dose was found to be intensity dependent with slightly higher effectiveness at the longer wavelengths. Effects of the order (or sequence) of exposure to three specific wavelengths indicated total yellowing obtained to be dependent on the order of exposure. (C) 1999 Elsevier Science Ltd. All rights reserved.