RADICAL FORMATION IN PEROXIDE-BLEACHED KRAFT PULP

The stability of hydrogen peroxide bleached kraft pulp against radical formation under different conditions was studied by the electron para magnetic resonance (EPR) technique. Among the conditions investigated were darkness and light, healing at elevated temperatures and UV radia tion. In addition, the effects of Fe and Mg ions and lignin content on relative radical concentrations were examined. Samples which represen ted commercial softwood and hardwood pulps were taken from the pulping process before final acidification and drying. All EPR spectra were m easured at room temperature and consisted of a single line with line w idth of about 0.8 mT. The middle point of the peak corresponds to the g value 2.004-2.005. The relative radical concentration was found to i ncrease least on storing in the dark and most On exposure to UV radiat ion. The relative radical concentration seemed to increase in two phas es: a faster initial increase and then a slower reaction. The observed photochromic effect showed a similar two-phase reaction.