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SCIENTIFIC PAPER |
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cerig.efpg.inpg.fr |
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Last update : Octobre, 28th 2005 |
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| Influence of pulp colour on bleachability Ways to improve the bleaching response of alkaline pulp |
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| Dominique Lachenal*, Christine Chirat*, Nicolas Benattar*, Yayha Hamzeh*, Nathalie Marlin*, Christelle Mateo**, Bernard Brochier*** | |||||||||||
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(*EFPG - Ecole Française de Papeterie et des Industries Graphiques **Tembec, *** Centre Technique du Papier) ATIP vol. 59, n°3, August-September 2005 |
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Chemical pulp were produced by conventional kraft process and by
alternative alkaline sulphur-free processes. They were bleached by ClO2
based ECF sequences. The Kraft pulps were easier to bleach. However all the
kraft pulps were not equal and some were harder to bleach than the others.
It was observed that the pulps which were more difficult to bleach were
richer in quinone groups. They were almost more coloured, with a more
pronounced reddish hue (a* coordinate of the L*a*b* values) which must be
given by quinone groups. Since quinones are not easily degraded by ClO2 it
was proposed that the pulp bleachability would related to the amount of
quinone groups, or to the level of a* coordinate.
The origin of quinone groups is not known. When AQ was used in the process, some of the detected quinones could be adsorbed residual AQ or AQ derivatives and possibly AQ condensation products with lignin. However since the simple NaOH cooking gave rise also to high contents of quinones, others origins have to be looked for. in the case of kraft cooking the reducing character of HS might hinder the formation of quinones
Ways to deal with the problem caused by the presence of quinones are proposed.
Full text available (pdf, 280 Ko)
