Paper properties of TMP and CTMP handsheets from spruce, as affected by the press load and temperature during sheet drying

The objective of this investigation was to evaluate how physical properties of laboratory sheets, made from different thermomechanical and chemithermomechanical pulps, depend on the pressure and temperature levels during pressing and drying. Sheets were formed from long fibre fractions, defined as the pulp retained on a 50 mesh wire in a Britt Dynamic Drainage Jar, and pressed and dried according to a number of different pressure and temperature settings. The results showed that there were large differences in the sheet properties depending on what type of method was used for pressing and drying. High freeness pulps were more sensitive than low freeness pulps to the methods used for pressing and drying. The results indicate that the difference in sheet properties between ISO and Rapid Kothen sheets may be explained by the fact that ISO sheets are wet pressed only at room temperature, the fibres are then allowed to spring back when pressure is released whereas the fibres in Rapid Kothen sheets are locked in their positions as the sheets are pressed and dried at high temperature until dry.