Xylanase treatment for the peroxide bleaching of oxygen delignified kraft pulps derived from three softwood species

Three commercial enzymes were used to evaluate the use of xylanase treatment for enhancing the peroxide bleaching of three oxygen delignified kraft pulps derived from the softwoods red cedar, Douglas fir, and western hemlock. Two bleaching sequences were examined, where the enzyme stage was placed before or between the two peroxide stages. The brightness gain achieved was dependent on the enzyme preparation, the origin of the pulp and the position of the enzyme stage in the bleaching sequence. In general, xylanase was found to enhance the pulp brightness achieved with two peroxide stages by 1-1.5% ISO. It could directly brighten oxygen delignified pulps before and after the first peroxide stage. Direct brightening of the oxygen delignified pulps, before peroxide bleaching, appeared to be correlated with the amount of UV-absorbing material solubilized during the enzyme stage.