Efeitos dos estágios de branqueamento com oxigênio, dióxido de cloro e peróxido de hidrogênio na qualidade das polpas kraft de Pinus taeda e de Eucalyptus spp

Abstract

The main objective of this study was to evaluate the effects of bleaching stages with oxygen (Pre-O2), chlorine dioxide and hydrogen peroxide in standard (O, A and P) and drastic (O*, D*E and P) conditions in the quality of kraft pulps of Pinus taeda and Eucalyptus spp. As research material, brown kraft pulps of Pinus taeda and Eucalyptus spp were used. The brown kraft pulps were bleached with oxygen under standard (O) and drastic (O*) conditions. Then kraft pulps of Pinus taeda and Eucalyptus spp. were bleached with hydrogen peroxide and chlorine dioxide followed by alkaline extraction in standard (P, DE) and drastic (P*, D*E) conditions. The bleaching stages were evaluated by kappa number, viscosity, pulp brightness and final pH and reagent consumption in the process. From these analyses the efficiency, selectivity and gain in brightness of bleaching stages were calculated. Finally, the bleached pulps were refined into four levels by refining the range of 45-55 °SR and evaluated for their physical and mechanical properties. It was concluded that the bleaching of kraft pulp by Pinus taeda stages O and O* showed higher delignification efficiency, selectivity and gain in brightness compared to the bleaching of kraft pulp from Eucalyptus spp. Possibly due to their higher content of lignin initial and lower content of Hex-A. The bleaching stages with chlorine dioxide delignification showed higher efficiency, selectivity and gain in brightness when compared with the stages with hydrogen peroxide for kraft pulps of Pinus taeda and Eucalyptus spp. The increased level of refinement resulted in an increase of the interfibrillar interactions and pulp strength. The higher the degree of pulp refining, the lower the drainability of the pulp and the greater the resistance to airflow (RPA). Bleached pulps of pine and eucalyptus had lower and higher RPA than brown pulp, respectively. For pine pulps, bleaching with chlorine dioxide resulted in pulps with higher RPA than peroxide bleaching. And this trend was the opposite for eucalyptus pulp. The bleaching of kraft pulps of pine and eucalyptus resulted in increased burst rate, and this effect was more pronounced for the stages in standard conditions. The stages with peroxide resulted in a higher rate than the burst stages with chlorine dioxide. The higher the refining energy spent, the higher tensile index, higher MOE for all pulps studied. For pine and eucalyptus pulps, the tensile index of bleached pulps are lower than those of brown pulp. The pine and eucalyptus pulps bleached with hydrogen peroxide resulted in lower and higher tensile index, respectively, when compared with the bleached with chlorine dioxide. The MOE and the TEA increase with the degree of refining. Bleached kraft pulps of pine and eucalyptus showed lower MOE and TEA than the brown pulp. The only exception is for the MOE and TEA pulp bleached pine in drastic conditions. For kraft pulp pine, bleaching with dioxide resulted in pulps with higher TEA and MOE when compared to pulps bleached with hydrogen peroxide. This trend is contrary to the eucalyptus pulps.