Design of multilayer paperboard for optimisedcompression strength

This master thesis was issued by BillerudKorsnäs Gruvön. The focus of this thesis was theinvestigation of the effects different fibre types has on the compression strength of the whole paper product. This stems from wanting to better understand how to produce a better paperboard construction with respect to stacking, storage, and transport. The goal, thus, was to learn how to better design multiply board - utilising laboratory test and a literature study. An alternative way of forming a multiply paperboard, stratified forming, has been studied - with insight in to the past and the present. A test plan was developed, the decision was to test bleached softwood kraft pulp (BSKP), unbleached softwood kraft pulp (UBSKP), neutral sulfite semi chemical Pulp (NSSC), andbleached hardwood kraft pulp (BHKP). The grammage was set to 140 g /m2 for all sheets. The combinations tested for the multilayered sheets were NSSC/BHKP, NSSC/BSKP, BSKP/BHKP,and BHKP/UBSKP with the configurations of 40/100, 70/70, and 100/40 g /m2 for all respective combinations. The method to produce a sheet for use in laboratory test was the dynamic sheet former(DSF). The sheets were then subsequently pressed and dried, and finally conditioned to 23°C and 50% RH. Measurements of the grammage and thickness, and analysis of the fractures, were conducted at Karlstad University, and the SCT were conducted at Gruvön in standard condition. The SCT results showed that for single sheets, BSKP was the strongest fibre type in its SCT index. The difference in strength between BSKP and UBSKP affirms the theory that bleaching improves the fibre-fibre bonding potential, which increases the strength. For two layered sheets, the highest SCT index was combinations BSKP/BHKP with the 70/70 configuration. When the difference was big between two different fibre types there also seemed to be a relation for the SCT index; if one fibre type is dominant, the SCT index shows a relation. For similar SCT indices, there was no relat