Bleaching Revisited: Impact of Oxidative and Reductive Bleaching Treatments on Cellulose and Paper

The present study compares five oxidative bleaching treatments (calcium hypochlorite, hydrogen peroxide in two concentrations, light bleaching, and potassium permanganate) and two reductive bleaching treatments (sodium borohydride and tert-butylaminoborane) with each other. Their impact was investigated on pure cellulose (Whatman filter paper) and on two different historic rag papers. The parameters investigated to evaluate the bleaching process are brightness, molecular weight, carbonyl and carboxyl group content. The bleached samples were analyzed directly after the bleaching treatments and additionally after accelerated aging. In summary, all bleaching methods tested lead to a clear increase in brightness, i.e. they are all efficient bleaching agents. Oxidative treatments tend to increase the amount of oxidized cellulose functionalities. However, there is no significant difference between most of the treatments, and all oxidative treatments have caused some damage on cellulose in some occasions. Both reducing treatments successfully decrease the amount of carbonyl groups and partially preserve the cellulose in terms of molecular weight stabilisation. Sodium borohydride is clearly the more efficient reducing agent.