The effect of high intensity mixing on the enzymatic hydrolysis of concentrated cellulose fiber suspensions.

Enzymatic hydrolysis of lignocellulosic biomass in a high shear environment was examined. The conversion of cellulose to glucose in samples mixed in a torque rheometer producing shear flows similar to those found in twin screw extruders was greater than that of unmixed samples. In addition, there is a synergistic effect of mixing and enzymatic hydrolysis; mixing increases the rate of cellulose conversion while the increased conversion facilitates mixing. The synergy appears to result in part from particle size reduction, which is more significant when hydrolysis occurs during intense mixing.

Pattern formation in flowing electrorheological fluids.

A two-fluid continuum model is developed to describe mass transport in electro- and magnetorheological suspensions. The particle flux is related to the field-induced stresses. Solutions of the resulting mass balance show column formation in the absence of flow, and stripe formation when a suspension is subjected simultaneously to an applied electric field and shear flow.

Properties of Fiber Flocs with Frictional and Attractive Interfiber Forces.

Theory and experiment suggest that the flocculation of non-Brownian, flexible fibers in flowing viscous media arises from the mechanical entanglement of fibers. We probe the role of frictional and attractive interfiber forces on fiber entanglement using a recently developed particle level simulation technique. With frictional and repulsive interparticle forces only, simulations capture flocculation in 0.125% by volume suspensions of fibers with properties similar to those of softwood pulp fibers. Here, model fibers elastically interlock-flocculation tendency and floc coherency are directly linked to elastic energy storage in fibers. By applying only repulsive and attractive interparticle forces of various strengths, sheared suspensions attain similar degrees of aggregation, and similar floc strengths, as in suspensions with interfiber friction. However, in the absence of interfiber friction, model fibers do not elastically interlock. We find friction to be an essential element in elastic entanglement of fibers. Simulations suggest that effective formation aids in papermaking should reduce interfiber friction under normal force loadings of 1-10 &mgr;N. Copyright 2000 Academic Press.