The Bleaching of Paper by Reduction with the Borane Tert-Butylamine Complex
| Main Authors: | , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0034-5806 |
| Online Access: | http://www.viks.sk/chk/res_1_97_1_11.doc |
| Abstract: | SUMMARIES. Acids, strong alkalies and many oxidizing agents cause degradation of cellulose, leading to the loss of paper resistance. The normal deacidification treatments with calcium compounds are able to transform the acid carboxyl groups into stable insoluble salts, but they do not react with the other carbonyl groups. The presence of these functions in the cellulose polymer makes the acid and alkaline hydrolysis easier and it is in part responsible for the yellowing of the paper. Much work has been undertaken to discover a compound with selective reducing power for these groups. The borane tert-butylamine complex gave particularly good results in reducing aldehydes and ketones and it is also able to produce an optical bleaching of paper. The aim of this experiment was to test its application on several kinds of printed paper with different graphic media and colours, as well as to optimise the time of application. The effectiveness of the borane tert-butylamine complex was demonstrated not only on artificially oxidized paper but also on original prints. The visual effect of all the prints was good. Concerning optimisation of the application time, we can conclude that ancient paper needs a long treatment time. We chose a time of 5 hours as a compromise between the needs of the paper and the stability of the inks. This time could be increased in the case of very oxidized paper, taking into account the stability and insolubility of the inks. COCLUSION. The effectiveness of the borane tert-butylamine complex has been demonstrated not only on artificially oxidized paper, but also on original prints. Moreover, the visual effect of all the prints is good. We have obtained greater contrast and the colours have all intensified, losing their yellow patina but without changing their aspect. As regards the optimisation of the application time, we can conclude that for the new artificially oxidized papers the degree of polymerization does not really change between 1 or 5 hours of immersion (see Table 7). The ancient paper needed a longer treatment time, as shown in Table 8, probably because the reduction had also to act on double bonds C = C on the cellulose ring. We chose a time of 5 hours for the prints as a compromise between the needs of the paper and the stability of the inks. The time could be increased in the case of very oxidized papers. We obtained better results on small pieces of unprinted paper from the aquatint after 5 days' immersion in the reducing agent (see Table 9). The only consideration to be taken into account with such a long time concerns the stability and insolubility' of the inks. For this reason the aquatint (the colour of which was very dark and brown) was treated for 2 days and not for 5 days. We should like to underline the point that the reducing agent should not be used on modern stamping inks (i.e. those used to stamp papers) as these rapidly disappear when the treated with the borane tert-butylamine complex. This product should be used under a hood, with protective gloves, and away from open flame; it must also be disposed of as a toxic product - it must not be washed down the drain. The EC risk classes are R 20/21/22 and R 36/37/38 (i.e.: harmful to inhale, ingest and have on the skin; and irritating to eyes, skin and respiratory system). The EC safety classes are S26 and 837/39 (i.e.: in case of contact with eyes immediately rinse with plenty7 of water, get medical attention; avoid contact with skin and eyes, wear rubber gloves and goggles). |
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| ISSN: | ISSN 0034-5806 |
