EFFECT OF SHEAR FIELDS ON HEMICELLULASE BINDING TO PULP FIBERS

Hemicellulase binding onto wood fiber was investigated in a turbulent mixing environment created by an axial flow impeller. The binding of t he enzyme was found to be a function of the intensity of agitation, re action time, and type of pulp. Enzyme binding to bleached softwood pul p increased with time initially, reaching a maximum after 5 min of mix ing. Binding of enzyme onto unbleached softwood pulp decreased with ti me and with increasing shear rate. It appeared that the higher the she ar rate, the lower was the binding of hemicellulase. The binding of en zyme to unbleached pulp was found to be lower than the binding to blea ched pulp. A lignin interference with the protein assay was observed w hen soluble lignin degradation products from unbleached softwood pulp were leached into the bulk solution. The leaching was found to be main ly a function of time, temperature, and pH. The rate of soluble lignin release was high in the early stages of mixing, but decreased with ti me. The activity of hemicellulase decreased with increased shear rate and with mixing time. Hemicellulase was resistant to deactivation at a low shear rate, but a higher shear rate deactivated the enzyme almost completely after 30 min.