The effect of adding thermo-mechanical pulp (TMP) in the middle layer of fine paper was studied. Bleached hardwood pulp made of birch (BH W) was stratified in top and bottom layers, while TMP was layered in the middle layer of hand sheets. The amount of TMP in the middle layer was varied from 10 to 40 percent of grammage. Chemical pulps were beaten with a Valley laboratory beater so that they had the same tensile index of dry paper as that of TMP. In addition to standard paper, technical properties, tensile and relaxation properties of dry and wet paper at high strain rate were studied. Decrease in brightness when replacing part of chemical pulp with TMP was evaluated for the layered structure. In addition, a new method based on Kubelka & Munk equations was developed to characterize the success of stratifying. Layering of TMP in the middle enhanced surface smoothness significantly compared to trials points, where pulps were mixed and homogenous. Adding of 40% of TMP pulp in the middle layer had no effect on surface properties of hand sheets. Addition ofTMP increased the bulk of uncalendered hand sheets significantly. Increase in TMP or stratifying the pulps had no effect on the tensile properties of dry paper. Tensile strength and residual tension, i.e. tension holding capacity of wet web, increased significantly when increasing TMP in furnish. Mixing TMP in pulps instead of stratifying resulted in higher tensile and residual tension values for wet samples. A theoretical study showed that addition of TMP decreases brightness significantly also with layered structure.
|Journal||Paperi ja puu|
|Publication status||Published - 2007|
|MoE publication type||B1 Article in a scientific magazine|
- Residual tension
- Wet paper