Evaluation of treatment of yellowing of historical papers using washing and reducing agents

Paper with any quality turn yellow over time and cellulose oxidation is one of the most important reasons of chain failure. Cellulose oxidation leads to the formation of light-absorbing groups which turns the historical papers to yellow color. In order to eliminate the yellow color of historical paper, washing with pure water might be efficient to remove some color degradation products from the paper structure and make the paper color lighter. Moreover, bleaching with reducing agents might be appliable to diminish the light-absorbing chromophores which make the the paper colorless and increase the brightness and whiteness. Here in this research, the appearance and structural characteristics of historical paper are evaluated after washing with pure water and regenerating agents. For this purpose, sodium borohydride and sodium dithionite are investigated as a reducing agent which are used generally in the paper industry to whiten wood pulp. The effect of reducing agent on historical paper are characterized by colorimetric tests, infrared spectroscopy, pH measurement and X-ray fluorescence. According to the experimental result, applying the reducing agent leads increase in brightness and a decrease in yellowness, the stability of fibers and ink, as well as an increase in the pH of the paper (especially the sample treated with sodium borohydride). In conclusion, the treatment with reducing agents indicated more efficiency in compare with the distilled water.