The degradation of cellulose with ferric and cupric ions in a low-acid medium

Metallic cations play an important role in cellulose degradation. Different mechanisms have been proposed for cellulose-metal interaction: a free radical mechanism in which the metal acts as a catalyst in the homolytic scission of the cellulose peroxide and a Lewis mechanism that involves either the semiacetalic oxygen on the anhydroglucose unit or the beta-glucosidic oxygen with formation of donor-accetor bonds. The first aim of our experimental work is to quantify the degradative effects induced by iron and copper ions in a low-acid medium and to verify whether experimental data are in agreement with one of the mechanisms proposed in the literature. All experimental results point out that iron ions act as a catalyst for the cleavage of cellulose 1-4-beta-glucosidic bond, whereas copper ions catalyze the oxidation on the anhydroglucose ring and are in agreement with the Lewis mechanism, which has now been experimentally verified. The second goal is to determine whether the use of a reducing material can obstacle the oxidation catalyzed by metals, producing optical bleaching of paper. The borane tert-butylamine complex shows good reducing power and permits optical bleaching of oxidized paper.