Avoiding slip in pulp suspension rheometry

Abstract

Pulp suspensions possess a yield stress that varies with concentration and fibre type, and understanding of this property is important to the pulp and paper industry. Unfortunately, pulp suspensions are highly susceptible to wall slip, which greatly complicates many rheological measurements including determination of the apparent yield stress. Using the vane method as a starting point, a slip-free method for measuring the apparent yield stress of pulp suspensions is developed. The findings from this method development are also used to assess the likelihood of slip having interfered with previous pulp rheometry studies and to offer some guidelines for the design of future experiments. Finally, the apparent yield stresses of suspensions of two National Institute of Standards and Technology reference pulps are determined for concentrations between 1% and 5% w/w, and the results contrasted with previous studies.