Bleaching chemicals have high operational costs and environmental impacts. Using xylanases on unbleached fiber is a sustainable way to make them more effective.

Residual lignin in unbleached chemical pulp gives it a dark brown color. To meet the high brightness and whiteness required in many grades of paper and board, mills must bleach the pulp. The most common bleaching chemicals include chlorine dioxide, hydrogen peroxide and caustic soda. These agents penetrate into the fiber wall to fragment, decolor and release entrapped lignin.

Xylanase action on the outer surfaces of unbleached chemical fiber opens the wall. That improves the penetration of bleaching agents as well as the diffusion of lignin from the fiber wall. Controlled hydrolysis of xylan at the fiber surface can also reduce the concentration of hexenuronic acid in unbleached pulp. This lowers wasteful consumption of bleaching chemical across the bleach line.  Also, xylanase action can liberate lignin by disrupting lignin carbohydrate complexes. These are just some of the mechanisms that provide the foundation of enzymatic bleach boosting.

Bleach boosting significantly reduces the need for chemicals in the bleach plant. In elemental chlorine-free (ECF) bleach lines, reducing chlorine dioxide lowers mill effluent toxicity. That's how xylanases help finished pulps get the right level of brightness. All with less bleaching chemistry and a lower environmental impact.