ABSTRACT
Paper and cardboard production has greatly increased in recent years, being one of the sectors of the forest industry with important expectations of expansion. Elemental chlorine free’ was made possible after the action of a pre-delignification step with pressurized oxygen, which leads to a pulp with considerably lower kappa number. Then the process can be based on the action of oxygen, ozone, hydrogen peroxide, or enzyme which replaces chlorine and chlorine dioxide bleaching. Xylanases are being employed as enzymatic pre-treatments in Kraft pulp bleaching process at mill scale in order to improve delignification by degradation of hemicelluloses. Consequently, due to market pressures and government norms, the pulp and paper industry has made substantial changes to conventional pulping and bleaching technologies. New operating policies were developed to minimize the pernicious impact of the free disposal of liquid residues in natural courses and landfills.
