MULTILAYERING OF FINE PAPER WITH 3-LAYER HEADBOX AND ROLL AND BLADE GAP FORMER
The aim of this study was on the layering of fine paper with a 3-layer headbox and roll blade gap former. It consisted of methodological development and laboratory scale studies, as well as layering studies on the pilot paper machine scale. The potential of layered structures in papermaking and the phenomena affecting layer mixing were also studied. Filler distributions were characterized by two parameters filler distribution shape and symmetry factors. The method developed made it possible to apply a statistical approach to experiments when studying the impact of typical wet end control parameters on the control of filler distributions and the contribution of filler distributions to paper quality parameters. A method by which the center layer fiber distribution may be characterized from the final paper is also presented. The method is based on the use of dyed fibers and a spectrofotometer. In addition, a laboratory device, a multilayer handsheet former for making layered structures, is presented. The process closely resembles a real continuous multilayer process by providing water phase interactions between layers during forming and two-sided dewatering characteristics. In a case study, retention chemical and filler layering with WFC base paper was performed by the multilayer handsheet former. Surface roughness decreased and brightness increased when the filler content in paper surfaces was increased. At constant filler content, paper strength increased as the filler concentration in the paper surfaces increased. The distinction between roll dewatering and blade dewatering in terms of layer mixing as well as differences in the mixing behavior of fibers and fillers in different dewatering phases was studied. Major fiber mixing takes place during the free jet and roll dewatering phase. In blade dewatering, fiber movements are related to formation improvements. The greatest mobility differences between fibers and fillers were found in the blade dewatering phase in roll and blade dewatering. Filler distributions were significantly affected during blade dewatering, with the mobility of the fibers remaining insignificant. The relationship between typical fine paper quality parameters and filler distributions was studied. Formation improvement and densification of the paper were achievable at the same running conditions. Low porosity was achieved by evenly distributed constituents (good formation) and a local rich filler concentration somewhere in the paper structure in the paper thickness direction. Oil absorption two-sidedness was minimized by symmetrical filler distributions. The combination of all these quality factors required the filler distribution to be symmetrical and as uor turned u-shaped as possible. The use of additives layering as a part of paper quality control was also studied. Multilayering was found to be an effective tool for the control of filler distributions. On the other hand it was shown that, in order to get optimized impact of the multilayering on quality properties, the other process variables also need to be controlled.
Sheet sealing in single and multilayer nanopapers
This study addresses one of the limiting factors for producing micro and nanofibrillated cellulose (MNFC)-containing papers: poor water removal properties. We focus on the sheet sealing phenomenon during dewatering. A modified dynamic drainage analyzer (DDA) is used to examine both multilayer and single layer forming of MNFC and pulp mixtures. It was found that a thin layer of pulp fibers on the exit layer with the grammage as low as 5 gsm was enough to significantly improve the dewatering of MNFC. For example, the dewatering rate of a furnish with 50% MNFC increased from 0.6 mL/s for a mixed system to 2 mL/s for multilayer system. However, the sheet sealing behavior was completely different when a lower proportion of MNFC was used. For the furnishes with less than 20% MNFC content, the mixed furnishes dewatered faster because the high amount of pulp fibers were able to prevent MNFC from enriching on the exit layer. Surprisingly, we found that very high final solids content (couch solids) could sometimes be achieved when MNFC was used. The highest solids contents achieved were 34 and 29% for the mixed systems. This compares to the 15–20% range typical of standard papermaking furnishes without MNFC. Overall, the results show that contrary to current thinking MNFC containing papers may lead, under some circumstances, to enhanced wire section dewatering.
The role of forensic epidemiology in evidence-based forensic medical practice
Objectives This thesis is based on 4 papers that were all written with the same intent, which was to describe and demonstrate how epidemiologic concepts and data can serve as a basis for improved v ...