1 Introduction

By the year 2000, the global production of paper and cardboard products was exceeding 300 Mt annually. In the 1990s, the average growth rate of the use of printing paper and related commodities was 3.2%. Although the emergence of new information and communication technology is expected to replace some of the traditional uses of paper, the development is likely to lead to new improved paper products, such as qualities suitable for digital printing. Trees and other fibrous plants also provide a renewable resource with a long industrial tradition of utilisation, which has also prepared the ground for future development of new fibre-based materials.

Pulp fibres made of wood are the basic raw material of the present pulp and paper industry. In order to obtain a final product with desired properties, various inorganic and organic chemicals are added to pulp at different stages of the manufacturing process. The interactions between the pulp fibres and these added chemicals determine the properties and quality of the resulting product. They also have a major influence on the stability and economics of the industrial process and have a prevalent effect on the maintenance of the equipment by ruling the conditions of their wear and corrosion. Therefore, the chemistry of pulp suspensions has gained considerable interest during the past decades. The importance of a proper understanding of the chemical state of pulp suspensions has been further increased by the often environmentally driven changes in pulp- and paper-making processes...