amenability of acacia and eucalyptus hardwood pulps to elemental chlorine-free bleaching: application and efficacy of microbial xylanase

This study outlines the results of a biobleaching study of acacia (A. mangium) and eucalyptus (E. globulus) hardwood kraft pulps with commercial xylanase (Optimase CX 72 L). The comparative study was carried out using an elemental chlorine-free (ECF) bleaching sequence (D0EPD1D2) after the enzyme (X) stage. The enzyme treatment resulted in improved optical properties with a reduction in bleach chemical consumption. At an equivalent bleach chemical consumption, a brightness gain of 2.1 and 1.7 units and a whiteness gain of 2.7 and 2.3 units were observed with xylanase treatment in acacia and eucalyptus pulps, respectively. In ECF bleaching using the D0EPD1D2 sequence, a final brightness was achieved to the extent of 90% ISO and 89% ISO for acacia and eucalyptus, respectively, at an equivalent charge of bleach chemicals. The post-color (PC) number was also reduced by up to 45% for both hardwood pulps compared with the control. The bleachability of acacia was observed to be significantly higher than that of eucalyptus. In addition, a 17.0% and 23.0% reduction in chlorine dioxide and sodium hydroxide, respectively, were obtained for both hardwood pulps after xylanase pre-bleaching, thus indicating an environmentally friendly approach to the process.