Enhancement of cellulase catalysis of wood pulp fiber by cationic polyelectrolytes

Cationic polyacrylamides (c-PAMs) are commonly used industrial flocculants. We have recently shown that they can significantly accelerate both the cellulase mediated hydrolysis of bleached paper fiber and the amylase catalyzed hydrolysis of cornstarch. A negative attribute is that they also agglomerate the fibers, which reduces fiber surface area. However, agitating the medium breaks up the flocs and removes this obstacle. The fibers are initially attacked by the enzyme at the kinked regions, which makes the fiber length drop rapidly. Because flocs are more difficult to form with shorter fibers, it is advantageous to delay the addition of c-PAM until the fiber is first shortened by the enzyme. The rate acceleration provided by the c-PAM is largely independent of its cationicity for both cellulose and amylase applications. It is proposed that the mechanism involves “patching”, a well-established phenomenon in paper science where the cationic c-PAM reduces the negative charge of the fiber. As the enzyme is also negative, patching reduces the zeta potential at the fiber surface and minimizes the charge repulsion between fiber and enzyme. Hence, the c-PAM indirectly promotes enzyme binding, which increases the rate of hydrolysis.