Paper and pulp

Paper is manufactured from pulped wood fibers, fillers, pigments and flocculent additives. Fillers, such as clays or chalk, are added to make the paper opaque. Dyes and pigments, such as titanium dioxide, are added to modify the brightness of the finished product. Improving the retention of these constituents is of prime importance during the paper making process.

Zeta potential, rheology and paper manufacture

The interaction of all of the components used on the physical properties of the product and efficiency of the paper making plant is complex, but there are two parameters that can be used to help – zeta potential and rheology. Zeta potential is the parameter that determines the electrical interaction between particles. A high zeta potential value, positive or negative, prevents flocculation. Reducing the value closer to zero allows particles to approach each other and flocculate. Changes in zeta potential can affect retention values, strength, pitch deposition, additive requirements and hence cost. In addition to the process itself, effective effluent treatment is highly dependent on the zeta potential of the materials discharged. Zeta potential measurements can be made quickly and easily using the Zetasizer Nano Z or Nano ZS.

The application of zeta potential measurements in a paper plant can be made in one of two ways. Firstly, a zeta potential profile can be made of a plant when everything is working well. Problems that arise later can be investigated by looking at variation in this norm. Secondly, existing processes can be improved by looking at the zeta potential at each stage of the process.

The zeta potential of pulp and other particles in the process may vary for a number of reasons, e.g. changes in refining, pH, pulp source, broke content and quantities of additives used. The effect of these various parameters on the zeta potential of pulp and other particles can be automatically studied by combining a Zetasizer Nano with Multipurpose Titrator (MPT-2). The MPT-2 can automate the measurement of the effect of pH, conductivity or additive concentration on the zeta potential of the dispersion.

Everything that was mentioned about zeta potential applies to the rheological properties as well. Rheological measurements are generally performed on bulk fluids requiring no dilution, enabling one to simulate how, for example, a paper coating material (with its complex composition) will perform when subjected to the high shear rates and stresses associated with the paper coating process. Costly production and product problems can be avoided by simulating these conditions in a rheometer first, or by using the rheometer to design the proper material composition before experiencing process problems and downtime.

Particle Sizing and Paper Manufacture

Particle size plays an important role in the paper making process. The particle size of the raw materials used in the process needs to be carefully monitored as variations may lead to poor quality products. For example, the size distribution of titanium dioxide particles used as a pigment in the paper making process will have an effect on the brightness of the finished product. Particle size measurements can be made using a Zetasizer if the size of the material is sufficiently small enough (typically less than 1 micron). Laser diffraction is another sizing technique suitable for the measurement of samples with larger size distributions. The Mastersizer 2000 with appropriate wet or dry sample dispersion units can be used for such applications.