The mechanical pulping industry faces continued rising energy costs and increasing competition for raw material. In order to produce improved products based on mechanical pulp at lower energy consumption it is necessary to have a better understanding of the development of fundamental fibre properties during the processes. In particular, changes in fibre collapsibility, fibre fibrillation and fibre and surface development are of great interest. The overall goal of the CRUW Mechanical Pulping project is “Support development of more energy efficient mechanical pulping processes by increasing the knowledge on ultrastructural phenomena in mechanical pulping”.
This project is working closely together with the Industrial Research College for Mechanical Pulping Technology bringing in the ultrastructural competence to more clearly understand and explain phenomena observed in these projects thus making it easier to develop new and improved processes to reduce energy consumption. This report presents results from CRUW Mechanical Pulping sub-project 1: ”Effect of different refining pressures and energy using spruce TMP pulps from Braviken”. The influence of temperature on the softening of lignin and hence improved (easier) fibre separation and treatment was noted earlier (Becker et al. 1977; Salmén 1984). Based on this knowledge, different process alternatives have been suggested to reduce energy demand for the refining process. One of the earliest publications on a technical system utilizing higher temperature and pressure was by Höglund et al. 1997 (Thermopulp). These results have been reproduced in many studies and are today considered general knowledge. There are however many practical problems with such a system. For example, the resulting very small refining gaps are difficult to control and it has therefore taken time to establish this technology in the industry. In the new TMP line at Braviken, the refiners are equipped to run at higher temperature/pressure than normal and it has therefore been interesting to study these pulps in order to explain the effects on pulp/fibres at an ultrastructural level. It should be noted that in a fibre-water-steam system, temperature and pressure are not independent variables and higher pressure means higher temperature and vice versa
