Viscosity Measurement
An international standard outlines the method for determining the limiting viscosity number of pulp in an ethylenediamine copper (II) complex solution. In pulp characterization, iso 5351 is used to estimate the average degree of polymerization of the cellulose molecules. This measurement does not apply to pulps that are insoluble in the copper solvent.
Solution Preparation
The test is performed by dissolving a dry sample of pulp in the cupriethylenediamine solvent to form a dilute solution. According to iso 5351, the flow time of this solution is measured through a glass capillary viscometer at a controlled temperature of twenty five degrees Celsius. This flow time is then compared to the flow time of the pure solvent to calculate the viscosity.
High viscosity values indicate longer cellulose chains, which are directly associated with high tear strength and tensile strength in the finished paper sheet.
Degradation Indicator
Pulp mills use this protocol to monitor the impact of cooking and bleaching stages on the structural integrity of the fibers. When the measured viscosity under iso 5351 falls below the acceptable threshold, it indicates that the chemical treatments have degraded the cellulose too severely. This degradation can lead to web breaks on the paper machine or poor performance in converted products.
By maintaining viscosity within target limits, mills can ensure that their pulp meets the strength requirements of demanding packaging applications.
