Biobleaching of cellulose pulp from wheat straw with enzymes and hydrogen peroxide

Abstract

The influence of the operating conditions (temperature, time, enzyme concentration, pH and pulp consistency) used in the enzymic step of an XP (Cartazyme–hydrogen peroxide) sequence for bleaching soda pulp from wheat straw on various properties of the resulting pulp (yield, brightness, viscosity and kappa number) and of the paper sheets obtained from it (brightness, breaking length, stretch, burst index and tear index) was studied. A 2 m−1 central composite rotatable design was used for this purpose. The results of the 27 experiments performed were processed using the BMDP software suite, which provided equations that reproduced the values of the dependent variables with errors less than 10%. Application of the steepest ascent method to the equations thus derived allowed the identification of the most suitable conditions for optimizing the values of the dependent variables. Based on these results, using an enzyme concentration of 0.04% by dry pulp weight, a temperature of 35°C, a pH of 4.7 and a consistency of 12% for 2 h in the enzymic step provided paper sheets of acceptable quality. The XP bleaching sequence decreases pulp yield by 28.3% (19.2% in step X and 9.1% in step P), and the kappa number and viscosity of the pulp by 37.2 and 6.4%, respectively; on the other hand, it increases the brightness, breaking length, stretch, burst index and tear index of the paper sheets obtained from the pulp by 42.7, 32.4, 21.9, 49.7 and 7.7%, respectively.