The effects of cationic starch wet-end addition on the mechanical and optical properties of clay ... more The effects of cationic starch wet-end addition on the mechanical and optical properties of clay loaded papers are discussed . It is shown that massive strength improvements can be achieved at high filler loadings with high starch additions . The properties of super-filled paper structures with filler loadings up to 90% are also reported . Cationic starch wet-end addition is superior to starch impregnation applications (e .g . size press) on highly filled structures . This behaviour is understood from the effect of wet-end starch addition on sheet consolidation (sheet density improvement) . Wet-end starch addition increases the drying stress built up during sheet consolidation. This increase is generally much higher for filled papers than for papers of zero filler content .
A suggested method to describe the creep behaviour of paperboard in edgewise compression works fo... more A suggested method to describe the creep behaviour of paperboard in edgewise compression works for paperboard in the same way as for other polymers . The relation between stress, strain and time may be determined by a simple equation involving two factors, a power function of time and a factor describing the non-linear behaviour of the stress-strain curve. For engineering purposes, it is an advantage to be able to design a given product in terms of stress and strain in isochronous curves . In some applications the critical design criteria may be governed by a critical strain . For such applications isometric curves, i.e. stress versus time at different strains, are used. The strain at break in compression of the investigated paperboards was found to be independent of time. The strain to break in creep was equal to the strain at break for stress-strain testing under straincontrol. By inserting the strain at break in creep in the creep equation, the isometric curve at break could be derived which by definition gives the relation between stress and lifetime. The data in this investigation indicate that a rather small number of specimens and a reasonably short creep time are sufficient to provide a
Synopsis Fibres from a bleached kraft pulp grafted with polystyrene by means of radiation initiat... more Synopsis Fibres from a bleached kraft pulp grafted with polystyrene by means of radiation initiation were studied. The purpose of grafting was to incorporate a polymer with a defined rheological behaviour, thereby changing the composition of the cell wall . The grafts had a polystyrene content ranging from 6 to 35 per cent by weight . In order to decrease the crystallinity of the cellulose, the fibres were treated with aqueous zinc solutions of 65 and 70 per cent concentration . In addition to decrystallisation effects these treatments caused chemical degradation and dissolution of the cellulose . Mechanical spectroscopy of the grafted fibres revealed an intense interaction between the polystyrene and the carbohydrate macromolecules . Apparently the treatment with zinc chloride causes degradation and structural breakdown of the grafted fibre which results in a less intense interaction between the cellulose and polystyrene phases . The results of creep measurements in water and toluene indicate that the polystyrene can control the properties of the matrix while the amorphous cellulose still governs the stress transfer between the reinforcing microfibrils . Under the chairmanship of Dr N. K. Bridge
This study was undertaken to analyse the effects of changes in moisture content on the three dime... more This study was undertaken to analyse the effects of changes in moisture content on the three dimensional hygroexpansivity of a typical fine paper, composed of a mixture of softwood and hardwood pulps. Unfilled and clay filled isotropic handsheets were made with different densities and degrees of shrinkage during drying. Changes in outer dimension and in pore volume of these different paper structures were analysed (...)
In this investigation three separate trials were run in which the effects of varying wet pressing... more In this investigation three separate trials were run in which the effects of varying wet pressing pressure, fiber orientation and drying condition on the hygroexpansivity of unfilled and filled papers were studied. Anisotropy of the elastic modulus was used to characterise the fiber orientation. The sheets were made of a mixture of softwood and hardwood pulps. The filler was either clay or chalk. The hygroexpansivity for unfilled and filled isotropic sheets dried under restraint was unaffected by density. However, the 40 percent clay-filled sheets had about 20 percent lower hygroexpansivity than the unfilled sheets. The lower hygroexpansivity of the filled sheets was attributed to the lower bonding degree caused by the interference of filler particles at fiber-to-fiber bond sites. For both unfilled and filled sheets the hygroexpansivity increased in the CD and decreased in the MD with increasing fiber orientation. At a given fiber orientation the filled sheet had a slightly lower hygroexpansivity in CD whereas the MD hygroexpansivity was approximately the same for filled and unfilled sheets at higher anisotropy of the elastic modulus. No difference was observed between chalk and clay-filled sheets. Shrinkage during drying increased the hygroexpansivity for both unfilled and filled sheets. At a given shrinkage level, the filled sheet always had a lower hygroexpansivity. sheets. In order to characterise the fiber orientation the anisotropy of the elastic modulus was measured . The sheets were made of a mixture of softwood and hardwood pulps. The filler was either clay or chalk. A typical machine-made paper has a predominantly machine direction (MD) fiber orientation, and is often stretched in the MD and allowed to shrink in the cross machine direction (CD) during the drying process. It is therefore difficult to separate the effects of fiber orientation and shrinkage on the hygroexpansivity of machine-made papers. Several investigations deal with the effects of papermaking parameters such as fiber orientation (Brecht, Hildenbrand 1960; de Ruvo et al. 1976), shrinkage during drying (Brecht et al. 1956; Newman 1963; Nordman 1958; Raderer 1967; SalmCn et al. 1987) and wet pressing pressure (SalmCn et al. 1987) on hygroexpansion. Only a few investigations deal with the influence of fillers on hygroexpansivity (Kilpper 1952; Lorey, Libby 1954; O'Leary et al. 1951; Weber et al. 1943). However, these studies have not shown any significant effects of fillers on hygroexpansion. On the other hand none of these investigations deals with the relative importance for hygroexpansivity of fillers and other pulp manufacturing and papermaking parameters such as wet pressing, fiber orientation and shrinkage during drying. This justifies further study of the subject.
Uneven print density, print mottle or mottle, call cause severe print quality problems and is a f... more Uneven print density, print mottle or mottle, call cause severe print quality problems and is a frequent problem for printers. Print mottle can occur ill sheet-fed offset due to several reasons related to both the paper and its coating and the printing press. The aim of the project was therefore to improve our knowledge of the influence on mottle related to the fountain solution which dampens the paper surface, water induced mottle. Pilot coated papers were produced and printed in a full-scale 4-colour sheet-fed offset printing press. During printing a specially designed test form was used. This must be used together with a blanket which has cut-out areas corresponding to the areas oil the test form. In this way it is possible to create a number of different printing situations oil the same printed paper sheet. The results from the print trials show that fountain solution from the previous printing unit can cause a decreased print density and dot gain. Water induced print mottle is ...
NEW PRINCIPLES OF EVALUATION Tony Haraldsson, Christer Fellers and Petter Kolseth . STFI, Box 560... more NEW PRINCIPLES OF EVALUATION Tony Haraldsson, Christer Fellers and Petter Kolseth . STFI, Box 5604, 114 86 STOCKHOLM, Sweden THE EDGEWISE COMPRESSION CREEP OF PAPERBOARD A suggested method to describe the creep behaviour of paperboard in edgewise compression works for paperboard in the same way as for other polymers . The relation between stress, strain and time may be determined by a simple equation involving two factors, a power function of time and a factor describing the non-linear behaviour of the stress-strain curve . For engineering purposes, it is an advantage to be able to design a given product in terms of stress and strain in isochronous curves . In some applications the critical design criteria may be governed by a critical strain . For such applications isometric curves, i .e . stress versus time at different strains, are used . The strain at break in compression of the investigated paperboards was found to be independent of time . The strain to break in creep was equal...
The use of gray-balance control in press calibration for robust ICC color management in sheet-fed... more The use of gray-balance control in press calibration for robust ICC color management in sheet-fed offset is discussed. Gray-balance control is a way to calibrate printing presses. It is found possi ...
The tensile stress-strain properties and the dynamic mechanical properties at room temperature ha... more The tensile stress-strain properties and the dynamic mechanical properties at room temperature have been measured for paper sheets containing up to 60% by weight of clay. Addition of the clay filler drastically reduces the stiffness, strength and ductility of paper. The negative effect of the filler can to a large extent be counteracted by adding 5% cationic starch. Filled paper has a marked nonlinear viscoelastic character and the mechanical loss factor increases markedly with increasing clay content when no starch is added. This may be due to friction between individual clay particles. Starch addition reduces the loss factor to the same level as for unfilled paper. It is suggested that the properties and structure of a clay film in fibre crossings governs the performance of the filled paper.
ABSTRACT The color of a print is affected by ink spreading and lateral light scattering in the su... more ABSTRACT The color of a print is affected by ink spreading and lateral light scattering in the substrate, making printed dots appear larger. Characterization of physical and optical dot gain is crucial for the graphic arts and paper industries. We propose a novel approach to separate physical from optical dot gain by use of a high-resolution camera. This approach is based on the histogram of microscale images captured by the camera. Having determined the actual physical dot shape, we estimate the modulation transfer function (MTF) of the paper substrate. The proposed method is validated by comparing the estimated MTF of 11 offset printed coated papers to the MTF obtained from the unprinted papers using measured and Monte Carlo simulated edge responses.
A coarse thermomechanical Asplund pulp was prepared from Norway spruce (Picea abies). The pulp wa... more A coarse thermomechanical Asplund pulp was prepared from Norway spruce (Picea abies). The pulp was delignified to different degrees using acidified sodium chlorite. The swelling behavior (measured as water retention value = WRV) of the resulting pulps was studied under various chemical conditions (pH and conc. of NaC1). It is shown that chloritedelignified pulps have an appreciable polyelectrolytic character. Whereas the WRV of an Asplund pulp does not respond to changes in the chemical environment, the delignified pulp has a WRV of 155 at pH 3 and 250 at pH 9. Compared under the same chemical conditions, the WRV increases with increasing degree of delignification < 70%) and is approximately constant at high degrees ofdelignification (> 70%).
Cellulose hydrogels have been synthesized by reacting solutions of cellulose xanthate with differ... more Cellulose hydrogels have been synthesized by reacting solutions of cellulose xanthate with different amounts of epichlorohydrin (0-24% w/w on cellulose) after which the cellulose was regenerated. The weight fraction of crystalline cellulose, determined by density measurements, decreases with the extent of chemical crosslinking and was estimated to vary between 30 and 42% for dry gels. The degree of equilibrium swelling in water of the prepared hydrogels varied between 3.05 and 6.33 g water/g dry gel (g/g). The degree of swelling decreases with increasing chemical crosslinking. As a result of the irreversible changes occurring during drying, the degree of swelling in water can be reduced down to 0.74 g/g. According to density gradient column measurements, the partial specific volume of water is 0.865 cm3/g at water contents below 0.13 g/g. It is suggested that water having this partial specific volume is the specific hydration water. At higher water contents, the partial specific volume of gel water equals the specific volume of bulk water. It is implicit in the interpretation of the density data in terms of a two state model of gel water that the crystallinity of cellulose is independent of the water content. Depending on the degree of swelling, heat treatment resulted in either an irreversible increase or decrease of the degree of swelling.
A technique for the tensile testing of single wood pulp fibers in air and in water is described. ... more A technique for the tensile testing of single wood pulp fibers in air and in water is described. Successive loading-unloading tests with increasing loads showed that the immediate elastic recovery of the wood pulp fibers was a linear function of the removed load. The slope of the straight line is inversely proportional to the rigidity ofthe fibers. Creep curves were recorded at 50% relative humidity and in water. As the testing method involves the measurement of the elastic recovery, the effect on the strain of the irreversible extension of microcompressions and crimps is eliminated. The method presented in this paper may therefore be more accurate for the determination of rigidity than those which evaluate rigidity from stress-strain curves. The tensile testing technique was critically examined, with special emphasis on the reliability of the adhesive used in attaching the fibers to the testing apparatus. The calculated elastic moduli and the creep behavior agreed well with literature data.
The effects of cationic starch wet-end addition on the mechanical and optical properties of clay ... more The effects of cationic starch wet-end addition on the mechanical and optical properties of clay loaded papers are discussed . It is shown that massive strength improvements can be achieved at high filler loadings with high starch additions . The properties of super-filled paper structures with filler loadings up to 90% are also reported . Cationic starch wet-end addition is superior to starch impregnation applications (e .g . size press) on highly filled structures . This behaviour is understood from the effect of wet-end starch addition on sheet consolidation (sheet density improvement) . Wet-end starch addition increases the drying stress built up during sheet consolidation. This increase is generally much higher for filled papers than for papers of zero filler content .
A suggested method to describe the creep behaviour of paperboard in edgewise compression works fo... more A suggested method to describe the creep behaviour of paperboard in edgewise compression works for paperboard in the same way as for other polymers . The relation between stress, strain and time may be determined by a simple equation involving two factors, a power function of time and a factor describing the non-linear behaviour of the stress-strain curve. For engineering purposes, it is an advantage to be able to design a given product in terms of stress and strain in isochronous curves . In some applications the critical design criteria may be governed by a critical strain . For such applications isometric curves, i.e. stress versus time at different strains, are used. The strain at break in compression of the investigated paperboards was found to be independent of time. The strain to break in creep was equal to the strain at break for stress-strain testing under straincontrol. By inserting the strain at break in creep in the creep equation, the isometric curve at break could be derived which by definition gives the relation between stress and lifetime. The data in this investigation indicate that a rather small number of specimens and a reasonably short creep time are sufficient to provide a
Synopsis Fibres from a bleached kraft pulp grafted with polystyrene by means of radiation initiat... more Synopsis Fibres from a bleached kraft pulp grafted with polystyrene by means of radiation initiation were studied. The purpose of grafting was to incorporate a polymer with a defined rheological behaviour, thereby changing the composition of the cell wall . The grafts had a polystyrene content ranging from 6 to 35 per cent by weight . In order to decrease the crystallinity of the cellulose, the fibres were treated with aqueous zinc solutions of 65 and 70 per cent concentration . In addition to decrystallisation effects these treatments caused chemical degradation and dissolution of the cellulose . Mechanical spectroscopy of the grafted fibres revealed an intense interaction between the polystyrene and the carbohydrate macromolecules . Apparently the treatment with zinc chloride causes degradation and structural breakdown of the grafted fibre which results in a less intense interaction between the cellulose and polystyrene phases . The results of creep measurements in water and toluene indicate that the polystyrene can control the properties of the matrix while the amorphous cellulose still governs the stress transfer between the reinforcing microfibrils . Under the chairmanship of Dr N. K. Bridge
This study was undertaken to analyse the effects of changes in moisture content on the three dime... more This study was undertaken to analyse the effects of changes in moisture content on the three dimensional hygroexpansivity of a typical fine paper, composed of a mixture of softwood and hardwood pulps. Unfilled and clay filled isotropic handsheets were made with different densities and degrees of shrinkage during drying. Changes in outer dimension and in pore volume of these different paper structures were analysed (...)
In this investigation three separate trials were run in which the effects of varying wet pressing... more In this investigation three separate trials were run in which the effects of varying wet pressing pressure, fiber orientation and drying condition on the hygroexpansivity of unfilled and filled papers were studied. Anisotropy of the elastic modulus was used to characterise the fiber orientation. The sheets were made of a mixture of softwood and hardwood pulps. The filler was either clay or chalk. The hygroexpansivity for unfilled and filled isotropic sheets dried under restraint was unaffected by density. However, the 40 percent clay-filled sheets had about 20 percent lower hygroexpansivity than the unfilled sheets. The lower hygroexpansivity of the filled sheets was attributed to the lower bonding degree caused by the interference of filler particles at fiber-to-fiber bond sites. For both unfilled and filled sheets the hygroexpansivity increased in the CD and decreased in the MD with increasing fiber orientation. At a given fiber orientation the filled sheet had a slightly lower hygroexpansivity in CD whereas the MD hygroexpansivity was approximately the same for filled and unfilled sheets at higher anisotropy of the elastic modulus. No difference was observed between chalk and clay-filled sheets. Shrinkage during drying increased the hygroexpansivity for both unfilled and filled sheets. At a given shrinkage level, the filled sheet always had a lower hygroexpansivity. sheets. In order to characterise the fiber orientation the anisotropy of the elastic modulus was measured . The sheets were made of a mixture of softwood and hardwood pulps. The filler was either clay or chalk. A typical machine-made paper has a predominantly machine direction (MD) fiber orientation, and is often stretched in the MD and allowed to shrink in the cross machine direction (CD) during the drying process. It is therefore difficult to separate the effects of fiber orientation and shrinkage on the hygroexpansivity of machine-made papers. Several investigations deal with the effects of papermaking parameters such as fiber orientation (Brecht, Hildenbrand 1960; de Ruvo et al. 1976), shrinkage during drying (Brecht et al. 1956; Newman 1963; Nordman 1958; Raderer 1967; SalmCn et al. 1987) and wet pressing pressure (SalmCn et al. 1987) on hygroexpansion. Only a few investigations deal with the influence of fillers on hygroexpansivity (Kilpper 1952; Lorey, Libby 1954; O'Leary et al. 1951; Weber et al. 1943). However, these studies have not shown any significant effects of fillers on hygroexpansion. On the other hand none of these investigations deals with the relative importance for hygroexpansivity of fillers and other pulp manufacturing and papermaking parameters such as wet pressing, fiber orientation and shrinkage during drying. This justifies further study of the subject.
Uneven print density, print mottle or mottle, call cause severe print quality problems and is a f... more Uneven print density, print mottle or mottle, call cause severe print quality problems and is a frequent problem for printers. Print mottle can occur ill sheet-fed offset due to several reasons related to both the paper and its coating and the printing press. The aim of the project was therefore to improve our knowledge of the influence on mottle related to the fountain solution which dampens the paper surface, water induced mottle. Pilot coated papers were produced and printed in a full-scale 4-colour sheet-fed offset printing press. During printing a specially designed test form was used. This must be used together with a blanket which has cut-out areas corresponding to the areas oil the test form. In this way it is possible to create a number of different printing situations oil the same printed paper sheet. The results from the print trials show that fountain solution from the previous printing unit can cause a decreased print density and dot gain. Water induced print mottle is ...
NEW PRINCIPLES OF EVALUATION Tony Haraldsson, Christer Fellers and Petter Kolseth . STFI, Box 560... more NEW PRINCIPLES OF EVALUATION Tony Haraldsson, Christer Fellers and Petter Kolseth . STFI, Box 5604, 114 86 STOCKHOLM, Sweden THE EDGEWISE COMPRESSION CREEP OF PAPERBOARD A suggested method to describe the creep behaviour of paperboard in edgewise compression works for paperboard in the same way as for other polymers . The relation between stress, strain and time may be determined by a simple equation involving two factors, a power function of time and a factor describing the non-linear behaviour of the stress-strain curve . For engineering purposes, it is an advantage to be able to design a given product in terms of stress and strain in isochronous curves . In some applications the critical design criteria may be governed by a critical strain . For such applications isometric curves, i .e . stress versus time at different strains, are used . The strain at break in compression of the investigated paperboards was found to be independent of time . The strain to break in creep was equal...
The use of gray-balance control in press calibration for robust ICC color management in sheet-fed... more The use of gray-balance control in press calibration for robust ICC color management in sheet-fed offset is discussed. Gray-balance control is a way to calibrate printing presses. It is found possi ...
The tensile stress-strain properties and the dynamic mechanical properties at room temperature ha... more The tensile stress-strain properties and the dynamic mechanical properties at room temperature have been measured for paper sheets containing up to 60% by weight of clay. Addition of the clay filler drastically reduces the stiffness, strength and ductility of paper. The negative effect of the filler can to a large extent be counteracted by adding 5% cationic starch. Filled paper has a marked nonlinear viscoelastic character and the mechanical loss factor increases markedly with increasing clay content when no starch is added. This may be due to friction between individual clay particles. Starch addition reduces the loss factor to the same level as for unfilled paper. It is suggested that the properties and structure of a clay film in fibre crossings governs the performance of the filled paper.
ABSTRACT The color of a print is affected by ink spreading and lateral light scattering in the su... more ABSTRACT The color of a print is affected by ink spreading and lateral light scattering in the substrate, making printed dots appear larger. Characterization of physical and optical dot gain is crucial for the graphic arts and paper industries. We propose a novel approach to separate physical from optical dot gain by use of a high-resolution camera. This approach is based on the histogram of microscale images captured by the camera. Having determined the actual physical dot shape, we estimate the modulation transfer function (MTF) of the paper substrate. The proposed method is validated by comparing the estimated MTF of 11 offset printed coated papers to the MTF obtained from the unprinted papers using measured and Monte Carlo simulated edge responses.
A coarse thermomechanical Asplund pulp was prepared from Norway spruce (Picea abies). The pulp wa... more A coarse thermomechanical Asplund pulp was prepared from Norway spruce (Picea abies). The pulp was delignified to different degrees using acidified sodium chlorite. The swelling behavior (measured as water retention value = WRV) of the resulting pulps was studied under various chemical conditions (pH and conc. of NaC1). It is shown that chloritedelignified pulps have an appreciable polyelectrolytic character. Whereas the WRV of an Asplund pulp does not respond to changes in the chemical environment, the delignified pulp has a WRV of 155 at pH 3 and 250 at pH 9. Compared under the same chemical conditions, the WRV increases with increasing degree of delignification < 70%) and is approximately constant at high degrees ofdelignification (> 70%).
Cellulose hydrogels have been synthesized by reacting solutions of cellulose xanthate with differ... more Cellulose hydrogels have been synthesized by reacting solutions of cellulose xanthate with different amounts of epichlorohydrin (0-24% w/w on cellulose) after which the cellulose was regenerated. The weight fraction of crystalline cellulose, determined by density measurements, decreases with the extent of chemical crosslinking and was estimated to vary between 30 and 42% for dry gels. The degree of equilibrium swelling in water of the prepared hydrogels varied between 3.05 and 6.33 g water/g dry gel (g/g). The degree of swelling decreases with increasing chemical crosslinking. As a result of the irreversible changes occurring during drying, the degree of swelling in water can be reduced down to 0.74 g/g. According to density gradient column measurements, the partial specific volume of water is 0.865 cm3/g at water contents below 0.13 g/g. It is suggested that water having this partial specific volume is the specific hydration water. At higher water contents, the partial specific volume of gel water equals the specific volume of bulk water. It is implicit in the interpretation of the density data in terms of a two state model of gel water that the crystallinity of cellulose is independent of the water content. Depending on the degree of swelling, heat treatment resulted in either an irreversible increase or decrease of the degree of swelling.
A technique for the tensile testing of single wood pulp fibers in air and in water is described. ... more A technique for the tensile testing of single wood pulp fibers in air and in water is described. Successive loading-unloading tests with increasing loads showed that the immediate elastic recovery of the wood pulp fibers was a linear function of the removed load. The slope of the straight line is inversely proportional to the rigidity ofthe fibers. Creep curves were recorded at 50% relative humidity and in water. As the testing method involves the measurement of the elastic recovery, the effect on the strain of the irreversible extension of microcompressions and crimps is eliminated. The method presented in this paper may therefore be more accurate for the determination of rigidity than those which evaluate rigidity from stress-strain curves. The tensile testing technique was critically examined, with special emphasis on the reliability of the adhesive used in attaching the fibers to the testing apparatus. The calculated elastic moduli and the creep behavior agreed well with literature data.
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