The Degradation of Cellulose with Ferric and Cupric Ions in a Low-acid Medium
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0034-5806 |
| Online Access: | http://www.viks.sk/chk/res_3_96_165_183.doc |
| Abstract: | Conclusions. All experimental results point out that: ˙ Iron ions act as a catalyst for the cleavage of cellulose 1-4--glucosidic bond, whereas copper ions catalyst the oxidation on the anhydroglucose ring. The Lewis mechanism (Fig. 5), until now only postulated, is therefore experimentally verified. ˙ Measurements of average "cold" and "hot" degree of polymerization, statistically analyzed, coupled with the carboxyl content determinations, are good indicators of oxidative mechanisms in the cellulose degradation. ˙ The borane tert-butylamine complex has good reducing power and permits an optical bleaching of oxidized paper (Fig. 16). The evidence of two different mechanisms for the iron-cellulose and copper-cellulose interactions induces us to discuss again deacidification: if the copper content in paper is high, the use of strong deacidification products can be dangerous for the paper conservation, inducing p-alkoxy elimination mechanisms. In this case it would be convenient to implement a preventive reduction. We stress that it is necessary, before using the reducing agent, to test that dyes, especially those containing carbonyl groups, are stable with treatment. Summaries. 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 -glucosidic oxygen with formation of donor-accetor bonds. The first aim of our experimental work is to quantify the degra-dative 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 l-4--glu-cosidic 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. |
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| ISSN: | ISSN 0034-5806 |
