The Influence of Modified Starch on the Process Water Quality in Papermaking and the Paper Properties

The influence of modified (cationic) starch on the process water quality in papermaking and paper properties has been investigated. The experiments were conducted on sulfate hardwood pulp by applying both tap and paper mill process water. When process water is used, the retained amount of starch on fibers decreases, which most probably results from a partial neutralization of the cationic charge on modified starch, thereby reducing its attraction to the anionic groups on a fiber. By adding the modified starch, the turbidity of process water is to some extent reduced, indicating that the suspended organic substances are removed from process water. Due to starch accumulation, the load of process water by organic substances (determined via the TOC analysis) is not reduced, but is rather increased when the modified starch is added. In most cases, the addition of modified starch improved the investigated paper properties. However, these properties varied in correlation with the quality of the used water, despite the fact that the dosage of modified starch remained constant. This demonstrates the influence of process water quality, not only on the paper properties, but also on the efficiency of process chemicals, such as the modified starch, in the papermaking process.