Energy reduction of refining by cellulases

The effect of three different commercial cellulase treatments applied on softwood bleached kraft pulp before the refining step was studied. Disc refining was applied under similar conditions as usual in paper mills. Two cellulase treatments allowed an energy saving of 20% to reach a given drainage index or breaking length. Water retention value (WRV), which characterizes the water absorption inside the fibre wall, was increased by the cellulase treatment. However, tear index losses were observed upon enzyme treatment. The third cellulase did not have an impact either on any parameters of the refining or on the pulp properties, except WRV. Viscosity measurements showed that the two first cellulases have strong endoglucanase activities but are lacking exoglucanase activities. Probably, endoglucanase activity weakens the fibre structure by generation of weak points or kinks. This hypothesis would explain the important cutting and fibrillation phenomena observed in the case of these two cellulases. It can be concluded that cellulase treatment could save 20% of electrical energy needed for refining, i.e., 50 kWh t(-1), if a paper quality with a high tensile resistance but lowered tear strength is acceptable.