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TCF bleaching of hardwood pulps obtained in organic acid media: Production of viscose-grade pulps

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Abstract

High-purity, viscose-grade pulps have been produced by means of delignification (in media containing formic or acetic acid) and TCF bleaching (using a E(O)ZP sequence). Aspen or Eucalyptus globulus wood chips were treated in media made up of either acetic acid, water and HCl or formic acid, water and hydrogen peroxide (Acetosolv and Milox technologies). Under selected conditions, unbleached pulps with kappa numbers in the range 14.0–28.5 were obtained at 50.0–53.7% pulp yield. These samples were subjected to E(O)ZP bleaching to reach the viscose-grade target values for chemical and physicochemical properties. Among the pulps tested, the bleached Milox pulp from Eucalyptus wood showed the best properties to be used for viscose manufacture (pentosan content of 1.4%, SCAN viscosity of 598 mL/g, ISO brightness of 89.9% and alkaline resistances of 90.1% and 97.0% in the R-10 and R-18 tests).

Zusammenfassung

Hochreine und holzviskose Zellstoffe wurden hergestellt mittels Delignifizierung (in Medien, die Ameisen- oder Essigsäure enthielten) sowie TCF-Bleiche (mittels Verwendung einer E(O)ZP Sequenz). Espen oder Eucalyptus globulus Holzspäne wurden in Medien behandelt, die entweder aus Essigsäure, Wasser und HCl oder Ameisensäure zubereitet wurden. (Acetosolv und Milox Technologien). Unter ausgewählten Bedingungen wurden ungebleichte Zellstoffe mit kappa-Zahlen in einer Bandbreite von 14,0–28.5 bei 50,0–53,7% Zellstoffausbeute erhalten. Diese Proben wurden einer E(O)ZP-Bleiche unterzogen, um die holzviskosen Zielwerte für chemische und physiochemische Eigenschaften zu erreichen. Unter den getesteten Zellstoffen zeigte der gebleichte Milox Zellstoff aus Eucalyptusholz die besten Eigenschaften für den Gebrauch zur Viskoseherstellung (Pentosangehalt 1,4%, SCAN Viskosität von 598mL/g, ISO-Helligkeit von 89,9% und Alkalinresistenz von 90,1% sowie 97,0% in den R-10 und R-18 Tests).

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Acknowledgements

The authors are grateful to the Commission of the European Communities and to the Ministry of Education of Spain for the financial support of this work (in the framework of the Projects "New Dissolving Pulps", reference FAIR-CT98-3855-DG12-SSMI, and "Desarrollo de procesos con bajo impacto ambiental para la producción de pastas de celulosa de alta calidad", reference QUI99-0346). The authors wish to thank to Ms. Anita Mayrhofer, Ms. Michaela Mayr, Ms. Aida Ramos and Ms. Antonia Rodríguez for their excellent technical assistance.

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Correspondence to J. C. Parajó.

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Dapía, S., Sixta, H., Borgards, A. et al. TCF bleaching of hardwood pulps obtained in organic acid media: Production of viscose-grade pulps. Holz Roh Werkst 61, 363–368 (2003). https://doi.org/10.1007/s00107-003-0404-7

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