The influence of high temperature pressing on paper properties was investigated. Handsheets made of TMP, bleached and unbleached kraft pulp were pressed in a press simulator with the press surface heated to 300°C. The density, tensile strength and air permeance of the press dried sheets are compared with the values for conventionally pressed and dried reference sheets. The compression behaviour and the dryness increase of the sheets pressed at high temperature were also investigated. It was found that the compressibility of the sheets was significantly increased if the hot surface temperature was increased from 250°C to 100°C. A further increase to 300°C gave only a minor compressibility increase. The increase in density and tensile index for the press dried sheets is higher for the high yield, low refined sheets than for the bleached kraft sheets. The air permeance of the press dried sheets was significantly lower than that of the conventionally pressed and dried sheets for TMP and for the low refined unbleached kraft. The bleached sheets showed the reverse behaviour and the air permeance was higher after press drying. A hypothesis to explain this is presented.
Subject classification (UKÄ)
- Chemical Engineering