Charge balances of paper machine systems - A method of process optimization

In order to meet the present-day needs of paper manufacturing, it is impossible to dispense with a wide variety of chemical additives. In order to make effective use of these additives, it is essential to have a full understanding of the wet end chemistry. Electrokinetic processes play a major role in this and their basic principles are described in this paper. Following an introductory description of various measuring principles and measuring instruments to characterise charge states in pulp systems, the paper goes on to explain, with the aid of practical examples, the strengths and weaknesses of the individual processes and the possibilities that exist of utilising them for controlling the paper production process. An important aspect here are the retention phenomena, which in turn govern the paper proper?ies and the running behaviour of the paper machine and are also heavily influenced by strongly ionic polymers such as retention aids and wet-strength agents, but also by anionic trash. It has been found that, in laminate paper systems the zeta potential reacts very well to changes in the furnish composition and that by checking the zeta potential any drifting of the paper properties can be recognised in good time. In systems with a high content of anionic trash, however, such as occur in the production of packaging papers made of 100% waste paper, the zeta potential is less sensitive to changes in the composition of the furnish. In such cases a control of the titratable charge quantities and, based on this the controlled addition of trash catchers, provide a useful possibility of achieving uniformity in the paper production process.