Enzymatic pretreatment to enhance chemical bleaching of a kraft pulp

Enzymatic xylanases and laccases-rich filtrates were produced by Aspergillus sp and Phanerochaete chrysosporium ATCC 24725, respectively, using agroindustrial residues as the sole carbon source. Their stabilities on different pH, temperature and ionic salt conditions were evaluated kinetically, and it was also identified the presence of additional enzymatic activities. Finally, an enzymatic pretreatment of kraft pulp was conducted in order to improve the action of chemical compounds used later on. Enzyme filtrates were resistant to the presence of various ionic salts and denaturing solutions, and they had a good stability into a wide range of pH values (from 3 to 9), although they showed low stabilities at temperatures higher than 50°C. Xylanases and laccases were the predominant enzymatic activities observed on the corresponding filtrates. In addition, the enzyme-pretreated pulp had lower kappa number than the not pretreated control. On the other hand, the enzymatic pretreatment produced liquors that showed high contents of residual lignin and chromophore compounds, which indicate the positive action of enzymes on kraft pulp structure.