Use of Chelating Agent EDTA with Sodium Thiosulphate and Sodium Borohydride in Bleaching Treatment
| Main Authors: | , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0034-5806 |
| Online Access: | http://www.viks.sk/chk/res_4_97_191_200.doc |
| Abstract: | Conclusions. ˙ Chelating agent EDTA can be shown to be useful in the removal of iron and copper on cellulose fibres. The best approach to the removal of stains caused by iron and copper is the use of a reducing agent coupled with a chelating agent. ˙ EDTA improves the colour stability of papers treated with sodium thiosulphate, but does not benefit to the colour stability of paper treated with NaBH4. ˙ Supposedly, Fe and Cu ions, which remained in paper, were released from the complexes by chelating agent, they can be oxidized and the preliminary effect of EDTA is lessening in the course of time. ˙ Despite of the lower content of CHO groups after bleaching, the paper samples treated with EDTA indicate the tendency of CHO content to increase after accelerated ageing. ˙ It is necessary to introduce Mg and Ca ions back into the paper after treatment with EDTA. ˙ The use of EDTA in practical conservation is limited owing to it stimulating the adverse effect of ink corrosion. ˙ The mechanism of all reactions which take place in paper when EDTA is used as a chelating agent are still not clear and need more detailed investigations. Summaries. This article briefly reviews the use of chelating agent EDTA with sodium thiosulphate and sodium borohydride in bleaching treatment. A rag paper (1832) was chosen for experiments. Acid soluble iron and copper were measured and compared to the results obtained by using EDTA. Brightness and colour reversion were observed and the content of COOH and CHO groups were measured before and after the accelerated ageing of paper. It is shown that the chelating agent can be useful in the removal of iron and copper on cellulose fibres. The best approach seems to be the use of a reducing agent coupled with a chelating" agent. If sodium thiosulphate is used the colour stability of the treated paper is improved, but this is not the case with NaBH4. Altogether, the mechanisms of all reactions which take place in paper when EDTA is used are still not clear and need more detailed investigations. |
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| ISSN: | ISSN 0034-5806 |
