Evaluating chelating agents and their effects on cellulosic pulps during P-stage bleaching. Part 1: analytical method development

During peroxide bleaching of pulp (“P-stage”), the heavy metal ions must be removed from the pulp and inactivated by chelation before the bleaching to prevent undesired degradation of cellulose by reactive oxygen species. Ethylenediaminetetraacetic acid (EDTA) is mostly used as a chelating agent; however, it may soon be banned because of environmental concerns. Therefore, there is a demand for new chelating agents to replace EDTA, and a comprehensive analytical method is necessary to investigate their chelating ability and the effects on the pulp. In this study, an analytical sequence for evaluating chelating agents and oxidative damage to cellulose during chelation (Q-stage) and bleaching (P-stage) has been established and optimized. GPC provides the molar mass distribution and oxidative damage (as profiles of carbonyl groups relative to the molar mass distribution), and the metal content of the pulp was determined by ICP-OES. This method enables the analysis of the chelating potential of new chelating agents, with simultaneous determination of the impact on cellulose on a molecular level. Graphical abstract