Hannu Paulapuro

Microcrystalline Cellulose-Water Interaction—A Novel Approach Using Thermoporosimetry

AbstractPurpose. To study the physical state of water in microcrystalline cellulose (MCC) and in silicified microcrystalline cellulose wet masses and the effect of granulation on different water fractions. Methods. Thermoporosimetry, together with the solute exclusion technique, was used to measure different water fractions and pore size distributions of wet granules. To understand the effect of granulation on the physical state of water, both ungranulated and granulated wet masses were studied. In addition, dynamic and isothermal step melting procedures were compared. Results. Four distinct fractions of water (nonfreezing, freezing bound, free, and bulk water) could be detected in MCC wet masses. Granulation decreased the volume of bulk water and increased the volume of freezing bound and free water. Consequently, granulated wet masses were able to hold more water inside the particles compared to ungranulated wet masses. Thus, granulation had a similar effect on MCC as beating has on cellulose fibers in the papermaking process. Conclusions. Thermoporosimetry and solute exclusion increased the understanding of MCC-water interaction and showed how the physical state of water in MCC wet masses changes during granulation.

Novel nanostructured PCC fillers

New filler and pigment technologies are needed to improve the optical properties of paper. Filler contents in different paper grades are approaching the maximum levels achievable with current papermaking practices. Much work has been done to maximize the light scattering potential of fillers and pigments by modifying their particle size distribution or specific surface area. The refractive index (RI) is an optical constant of pigment, and less attention has been paid to the possibility of increasing this parameter. In the present study, a novel nanostructured filler-grade precipitated calcium carbonate (PCC) pigment was synthesized. Zinc-based nanostructures, physically contacted with the host PCC material, increase the differences in RI between filler-fiber and filler-air interfaces, yielding increased light scattering. The effective RI of the novel filler was measured using a method which combines a multi-function spectrometer with the immersion liquid method. This method enables effective RI measurement from pigment suspensions, irrespective of the shape, size, and nanostructures occurring on the host pigments. When compared to conventional PCC, the results gained with the nanostructured PCCs suggest an increase in the effective RI. When used as filler in paper, nanostructured PCC yields improved light scattering, i.e., better opacity.

New mechanical treatment for chemical pulp

Abstract This study presents a new method to modify chemical pulp mechanically using an ultra-fine friction grinder, which works in a different way compared with conventional refiners. It consists of two grinding stones: a lower rotating one and an upper stationary one. The pulp passing through the gap between the stone plates is subjected to compressive and shear forces. The results showed that the gap clearance of the grinder plays an important role in controlling the fibrillation of fibres and the specific energy. External fibrillation became a dominant effect at a larger gap, whereas internal fibrillation developed faster at a smaller gap. Fibres were modified mostly into fibrils at a much smaller gap. Scott bond strength of pulps treated in the grinder was better than that of Valley-beaten pulps. Pulp properties can be varied by adjusting the pulp consistency, rotating speed, grit size, the dullness of the plate surface, and the number of pulp recirculations.

Surface chemical composition of some non-wood pulps

Abstract The surface lignin and extractives coverage of some non-wood pulps (wheat straw, reed, bagasse, bamboo and kenaf bark) were investigated by means of ESCA and compared with wood pulps. Strong enrichment of lignin and extractives on the pulp fiber surface was found for all of the pulps. At the same bulk lignin content level, the surface lignin coverage was found to be higher in the non-wood pulp than in the softwood pulp. The possible reasons for this were examined.

Observations on interfibre bonding and fibre segment activation based on the strength properties of laboratory sheets

SUMMARY: The aim of this study was to gain better understanding of bonding and activation in paper and to clarify the relationships between these two phenomena and the strength properties of paper. Bonding and activation were studied through examining the mechanical properties of paper. Both inplane strength properties (tensile strength, tensile stiffness, elastic breaking strain and in-plane tear strength) and z-directional strength properties (Scott bond strength) were examined. The properties of fibre network were varied by beating of chemical pulp fibres and by introducing different levels of drying stress to the network at different solids contents. Different mixtures of chemical and mechanical pulps were used as well. As a generalisation, it can be said that the in-plane properties of laboratory sheets were improved by increasing drying stress. This improvement arises from increasing activation, ie. the removal of slackness and curls from the unbonded fibre segments within the network. Activation straightens those segments into load-bearing units. On the other hand, z-directional strength properties, or bond strength, in most cases decreased by increasing drying stress. The strain introduced to the network affects the bonded areas of fibres negatively, but the extent of this effect depends quite much on the fibre composition, degree of drying stress and the solids content at which strain has been introduced. It seems that the structure of the bonded area influences sheet behaviour and the development of strength properties significantly. Bonding and activation are both essential properties of fibre network in relation to its strength properties.

EFFECT OF FIBER FLOCCULATION AND FILLING DESIGN ON REFINER LOADABILITY AND REFINING CHARACTERISTICS

The loadability of a pulp refiner was studied using refiner data such as gap movement, total power, no-load power, and net refining power. Two different types of pulp and three different types of refiner filling were used in the study. The floc formation and floc size of each pulp was studied in a flow channel simulating filling grooves. The loadability of the pulp refiner was linked to refining effects such as fiber shortening, and internal and external fibrillation. The trapping point of the refiner, and therefore refiner loadability, was found to be more related to fiber characteristics such as fiber length and coarseness, while being less dependent on refining consistency in the range of 2.0-5.5%. The data on the formation of flocs and floc size was used to explain the trapping of fibers between refiner bars and the refiner gap width. Filling design characteristics such as groove width and cutting speed affect the gap width and trapping of flocs inside the refiner. Fillings with high cutting speed tend to break flocs composed of long and short fibers at the same rate and therefore both types of floc maintain the same gap width. On the other hand, wide-groove fillings with lower cutting speed have a gentler effect and the differences in fiber characteristics are easily reflected in the gap width and trapping point. Fillings with low cutting speed have a greater straightening effect than fiber cutting, whereas narrow-bar fillings have a more noticeable effect on fiber cutting, external fibrillation, and fiber swelling.