CELLULASE BINDING TO CELLULOSE FIBERS IN HIGH-SHEAR FIELDS

Cellulase binding onto cellulose fiber was investigated in a turbulent mixing environment created by an axial flow impeller. The binding of the enzyme was found to be associated with various process variables studied, e.g., intensity of agitation, reaction time, pulp consistency, pH, temperature, and concentration of enzyme. The similarity between trends in enzyme binding and enzyme activity confirmed that the reduction of binding with increasing intensity of agitation over time was due to denaturation of the enzyme by shear. Physical forces like shear can disrupt the structure of the enzyme resulting in the loss of binding ability and activity. It also appeared that mild mixing did not denature the enzyme, but rather the enzyme dispersed better into the pulp slurry, resulting in a higher percentage of enzyme bound to fiber. However, increasing shear resulted in a reduction in binding and activity. At a low rpm, the binding increased initially with time, reached a peak at about 3 to 5 min, and then decreased gradually. With respect to time and shear rate, the reduction in binding and activity was much more significant at 10 min of mixing. It is concluded that a high shear and/or a prolonged exposure to a low shear can disrupt the structure of enzyme resulting in the loss of binding ability and activity. At low enzyme concentrations, the binding of enzyme onto fiber increases with increasing concentration of enzyme. Similarly, the percentage of enzyme bound increased with increasing pulp consistency. Since cellulase needs mild temperatures and acidic environments to maintain its activity, high temperature and pH caused a reduction in binding. A pH of 4 and a temperature of 30 degrees C yielded the highest percent binding among the conditions studied.