resumo
This study investigates the effect of pulping time and process parameters on the content of hexenuronic acid (HexA) in Eucalyptus globulus kraft pulps. Under selected standard pulping conditions, the amount of HexA in pulps increases during cooking. This behavior, significantly different from that of softwood pulps, is tentatively attributed to the milder conditions used in the pulping or to topochemical effects rather than to differences in the chemical structure of the glucuronoxylans from hardwoods and softwoods. We found that, for the same kappa number (14, obtained by adjusting pulping time), the HexA content decreases when active alkali increases from 17% to 24% and increases with sulfidity in the range 15%-28%. A decrease in the HexA content occurs when the temperature rises from 150degreesC to 170degreesC and when liquor-to-wood ratio increases from 4 to 8. The variations observed are determined by two simultaneously occurring processes: HexA formation and degradation or dissolution with xylans. When the unbleached pulps with kappa number 14 were fully bleached by a DEDED sequence, we observed a general increase in chlorine dioxide consumption as the HexA of the unbleached pulp decreases.
palavras-chave
SOFTWOOD
categoria
Materials Science
autores
Daniel, AID; Neto, CP; Evtuguin, DV; Silvestre, AJD
nossos autores
Ana Isabel Dias Daniel
Investigador Principal
Armando Jorge Domingues Silvestre
Professor Catedrático
Carlos Pascoal Neto
Diretor do Raiz