Influência da madeira de clones de Eucalyptus spp. na deslignificação e na qualidade da polpa kraft

Abstract

Wood is the main raw-material for cellulose production and the wide variability in fundamental properties, such as anatomical, physical and chemical ones, may significantly affect its behavior during pulping and bleaching processes. The deep knowledge on the effect of those characteristics on the pulping process is crucial for the selection and improvement of clones, process optimization, improvement of the final product, and reduction of environmental impact in the industry. This work had the following objectives: to evaluate wood quality for cellulose production; to evaluate the relations between the process characteristics; and to evaluate the feasibility of multivariate statistical techniques as tools for Eucalyptus spp. clone selection destined to cellulose pulp production. Nine commercial Eucalyptus spp. clones were evaluated. The following wood properties were analyzed: basic density; extractive, ash, and carbohydrate (monomeric sugars, cellulose, hemicelluloses) contents; and uronic acids. The pulps were produced under the following operational conditions: 400 g of wood chips; maximum temperature of 170 oC; time until maximum temperature is reached of 90 minutes; reaction time kept at maximum temperature of 60 minutes. Alkali loads were experimentally established in order to obtain pulps with Kappa number 17 ± 0.5. Three cooking procedures were carried out for each clone, totalizing 27 pulps. The following characteristics of the pulps were evaluated: ISO-whiteness; viscosity; purified yield; total yield; residual lignin; carbohydrates; uronic acids; and hexenuronic acids. Solid content and pH were evaluated for the black liquor. Wood properties depicted values compatible with those of literature for Eucalyptus spp. destined to cellulose production. Values of pulp characteristics were also considered adequate, especially those obtained for pulp yield. Variation in alkali loads significantly affected the following pulp properties: hexenuronic acids; residual lignin; purified yield; total yield/Kappa relation; and solid content of the black liquor. Hexenuronic acids variation from 40.18 to 53.56 mmol.kg-1 had significant effect on the following pulp properties: residual lignin; purified yield; total yield/kappa relation; and solid content of the black liquor. Positive linear correlation was found between xylose content of the pulp and viscosity. Principal components analysis and grouping allowed the establishment of 3 groups. Clones D, E and G showed the best genetic materials for cellulose pulp production, while clone F and H presented the worst performance for this purpose.