The effect of Talaromyces thermophilus cellulase-free xylanase and commercial laccase on lignocellulosic components during the bleaching of kraft pulp

Abstract

Biobleaching studies of kraft pulp with cellulase-free xylanase produced by Talaromyces thermophilus and commercial laccase were done in order to investigate their potential applications in various industries. The efficacy of xylanase in reducing the amount of bleaching agent needed was demonstrated by using 20 IU xylanase per gram of oven-dried pulp at 3% concentration prior to the bleaching at pH 7.0 and 70 °C for 120 min of treatment. This amount of xylanase acts on hemicelluloses; it releases chromophores and reduced sugars, and shows the further, decrease in kappa number of pulp without much change in viscosity. Also, a commercial laccase used at 40 IU per gram of oven-dry pulp at 3% concentration exhibited the optimum bleach boosting of the pulp at pH 7.0 and 50 °C after 180 min of treatment. Enzymatic treatment of pulp with the two enzymes (xylanase and laccase) required a smaller amount of chlorine to obtain the same results when pulp was treated with chlorine only. Enzymatic pretreatment of pulp followed by a chemical treatment with 3% NaOCl makes it possible to obtain the same results with chemicals at 7% NaOCl, resulting in 42% reduction in chlorine consumption.