Morphological characteristics of TMP fibres as affected by the rotational speed of the refiner

The main fibre characteristics under study were 1) fibre wall thickness and 2) the degree of longitudinal splitting of the cell wall, for TMP fibres. Both characteristics are considered to affect the attainable paper smoothne ss. Both single (SD) and double disc (DD) refining was studied, and the fib re properties were assessed after each stage by high resolution SEM microsc opy. For a given energy input, raised rotational speed of the refiner in th e primary stage reduced fibre wall thickness. This effect was more pronounc ed for double than for single disc refining. When the different first stage processes were followed by constant conditions in subsequent refining stag es, the differences in wall thickness diminished. Raised speed in the prima ry stage also caused increased degree of fibre splitting, for both refining modes. The difference in the fraction of split fibres subsisted in followi ng refining stages. The cross-sectional fibre characteristics were found to be little affected by varying the rotational speed in the second stage. The results obtained in this study indicate that high rotational speed can give significant energy savings.