Enhancement of Pulp Brightness and Yield in ECF Bleaching Using Xylanase Treatment: A Comparative Study on Different Wood Species

Bleaching is a process used to remove lignin from wood fibers, which contributes to their light brown-yellowing color.The brightness reversion of chemical pulp comes from the residual lignin left in the pulp.Pulp, a wood fiber, contains lignocellulose, extractive, and ash.In conventional ECF (Elementally Chlorine Free) bleaching, lignin degraded in cooking is removed before bleaching.Xylanase treatment is performed before O2 delignification and ECF bleaching to allow oxygen and bleach chemicals to penetrate the lignocellulose structure and peel off the lignin intact.This process must be done in the lignocellulose structure rather than the cellulose molecule to avoid cellulose degradation impacting product yield and fiber properties.This experiment involved 250 g of ovendry, unbleached pulp.It involved ECF bleaching O-D-E-D stages, including oxygen delignification, Chlorine dioxide bleaching, and extraction with dilute NaOH solution in pressurized oxygen.The pulp was centrifuged between each step to remove liquor and displaced with water with a dilution factor of 3 kg.The standard method used was the SCAN method.The research results showed that higher brightness led to fewer yield losses.This phenomenon occurs due to the more significant amount of lignin removal.After bleaching, Eucalyptus Camaldulensis maintained a yield value of 80.22%, the highest result among the three samples tested.The soft matrix in Eucalyptus Camaldulensis can cover the S2 layer and protect the boundary pith, making it more readily dissolved by xylanase treatment than Acacia Mangium and Mixed Tropical Hardwood.Additionally, Eucalyptus Camaldulensis has larger pore sizes, vessels, and lumens, which enhance accessibility for xylanase enzymes and bleaching chemicals to reach the Lignin-Cellulose-Hemicellulose matrix compared to Acacia Mangium and Mixed Tropical Hardwood.Thus, Eucalyptus Camaldulensis demonstrates better performance in the bleaching process regarding lignin removal and the efficiency of enzyme and chemical usage.