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Four major toners are used in the printing industry, cyan, magenta, yellow and black (Key) for making color images on paper. Paper brands suitable for printing have thin mineral/latex coatings, and toners are applied on top of the coating in the printing process. Chemical compositions from toner to toner, as well as from coating to coating, vary according to the needs of the end user. Interactions between the toner and the coating define the final color formation of the images in printing. Hence, it is important to study characteristics and dynamics of toners on coated papers. In this paper, we have used laser-induced plasma spectroscopy (LIBS) to provide information on elemental distributions of the toner and the coating layers on three coated papers and the base paper at a sub-micrometer resolution. Ablation crater depth profiles in the three different material layers were converted into metric scale by combining elemental information from the LIBS measurements and optical profilometry. Ablation efficiencies for a toner of 150 nm/pulse, for a coating of approximately 350 nm/pulse and for a base paper of approximately 1 μm at a fluence of 0.6 J/cm2 of an ArF excimer laser were determined. Using these results, the average layer thicknesses of the toner and the coating layers were evaluated. The detailed analysis of the elemental profiles of the two cyan toners studied revealed strong accumulation of silicon and titanium compounds of the toner on the toner–air interface but also on the toner–coating interface, but to a much smaller extent. The observation reveals the significance of toner component diffusion due to substrate–machine interaction in the printing process. Such diffusion processes must have an important role in final color formation of the images in printing. The method developed provides a unique and accurate means to study toner diffusion processes in coated papers under printing conditions.

The effects of bio-based strengthening agents and mineral filling procedure on the 3D elongation of chemi-thermomechanical pulp (CTMP) handsheets with and without mineral (PCC) filling have been investigated. The 3D elongation was measured using a press-forming machine equipped with a special converting tool. The strength of the handsheets was altered using either cationic starch or microfibrillated cellulose. Precipitated calcium carbonate (PCC) was added to the furnish either as a slurry or by precipitation of nano-sized PCC onto and into the CTMP fibre. The 3D elongation of unfilled sheets was increased by the dry-strengthening agents, but no evidence on the theorised positive effect of mineral fill on 3D elongation was seen in either filling method. The performance of the strengthening agent depended on whether the PCC was as slurry or as a precipitated PCC-CTMP. The starch was more effective with PCC-CTMP than when the PCC was added directly as a slurry to the furnish, whereas the opposite was observed with microfibrillated cellulose. The 3D elongation correlated positively with the tensile strength, bursting strength, tensile stiffness, elastic modulus and bending stiffness, even when the sheet composition was varied, but neither the strengthening agent nor the method of PCC addition affected the 3D elongation beyond what was expectable based on the tensile strength of the sheets. Finally, mechanisms affecting the properties that correlated with the 3D elongation are discussed.

Foams were prepared from hydrophobically modified ethyl(hydroxyethyl) cellulose (EHEC), methyl nanocellulose, and native microfibrillated cellulose (MFC). Their film- and foam-forming abilities, stabilities, and suitabilities for foam coating on different substrates were investigated. The role of EHEC as a polymeric stabilizing agent was also studied. The EHEC-MFC foams showed greater stability and water-holding ability under pressurized dewatering than MFC foams prepared in the presence of a surfactant. A foam could be created with methyl nanocellulose without any foaming agent. Selected nanocellulose gels and foam formulations were used to coat various substrates. The surface was efficiently closed by gel and foam coatings prepared from the methyl nanocellulose and EHEC solutions, which was ascribed to good coating holdout. Coatings on papers with different levels of smoothness/density and hydrophobicity/ hydrophilicity confirmed that foam-substrate interactions affected the coat quality. The air permeance was reduced by 99% and 64% with a methyl nanocellulose coating and an EHEC-MFC coating, respectively. An EHEC-MFC coating created a hydrophobic surface on a hydrophilic substrate, and methyl nanocellulose improved the oil resistance even at a low coat weight.

The use of nanomaterials and polymers from renewable resources is important in the search for sustainable alternatives to plastic-based packaging materials and films. In this work, self-supporting thin films prepared from derivatized and non-derivatized nanocellulose and cellulose derivatives were studied. The effect of drying temperature on the film-forming behavior of compositions comprising hydrophobically modified ethyl(hydroxyethyl)cellulose (EHEC), native microfibrillated cellulose (MFC) and nanocellulose made from methyl cellulose was determined. The interaction between the components was assessed from viscosity measurements made at different temperatures, the result being linked to a thermal-dependent association during liquid evaporation, and the subsequent barrier and film-forming properties. The effect of temperature on suspensions was clearly different between the materials, confirming that there were differences in interaction and association between EHEC–MFC and methyl nanocellulose–MFC compositions. The amphiphilic EHEC affected both the suspension homogeneity and the film properties. Air bubbles were formed under certain conditions and composition particularly in MFC films, dependent on the drying procedure. The presence of air bubbles did not affect the oxygen transmission rate or the oil and grease resistance. An increasing amount of MFC improved the oxygen barrier properties of the films.

Abstract Composite sheets consisting of elongated and aggregated cationically charged precipitated calcium carbonate (PCC) and native microfibrillated cellulose (MFC) were prepared with a wet laying method. The furnishes were prepared with and without an anionic flocculating agent (polyacrylamide) in order to adjust the structure of the sheet. The samples were compressed (densified) in order to determine the particle and microfibrillated cellulose-PCC structure coalescence and densification, as well as its subsequent influence on liquid absorption behavior. The densification affected both the vertical and lateral distribution of PCC, but the flocculating agent enhanced the compression stability and stabilized the sheets against PCC material flow. The differences between the sheets made with and without the flocculation aid affected the absorption of an anionic dye-based fluid ink, which was evident as a higher print density and less print bleeding. The absorption behavior was dependent on the sheet structure, especially on the PCC distribution within the sheets. Finally, the role of MFC on floc structure and floc formation is discussed. Graphic abstract

The temperature-dependent association between methyl nanocellulose and hydrophobically modified ethyl(hydroxyethyl)cellulose (EHEC) was determined. Methyl nanocellulose was mixed under different concentrations with EHEC in aqueous media. The hydrophobic association, cloud point and temperature-dependent flocculation were studied using turbidity, rheometry and laser diffraction analysis. The phase separation of EHEC samples containing different amounts of methyl nanocellulose in 1.0 wt% solution was measured between 20 and 70 °C, showing that the cloud point of the solutions increased with increasing nanocellulose content. An increase in the low shear viscosity and gelation behavior of the mixture with the highest methyl nanocellulose content in conjunction with changes in cloud point indicated that the hydrophobic nanocellulose strengthened the hydrophobic association and the gel network. A bimodal particle size distribution was observed for both the pure EHEC and hydrophobically modified nanocellulose reference solutions, whereas the mixture had a trimodal particle size distribution when being diluted. The colloidal stability and re-structuring mechanism of the dilute methyl nanocellulose suspension after shear and the role of birefringence are discussed.

Abstract CaCO3-pulp composite was prepared via precipitation of calcium hydroxide in the presence of pulp. In order to investigate the precipitation selectivity and mechanism, the substrate pulps and the obtained composites were fractionated (R30, R100, R200, R400 and a sedimented fraction that passed the 400 mesh wire) using a Bauer-McNett unit. The main fractionation criterion was therefore fiber length. The pulp used was CTMP (chemithermomechanical pulp), yielding a precipitated calcium carbonate-chemithermomechanical pulp (PCC-CTMP) composite with a targeted PCC-to-CTMP ratio of 1:1. The PCC consisted primarily of nano-sized primary particles which formed aggregates and clusters on the fibers. When the fiber morphology, zeta potential and surface charge density of the fractions were determined, a correlation was found between the surface charge density of the CTMP and the ash content of the corresponding PCC-CTMP fractions. This supports the hypothesis that the precipitation on the CTMP fiber is driven by the charge interparticle interaction. The use of refined CTMP furnishes and fractionation of the PCC-CTMP furnishes demonstrates that PCC is preferably fixed on fines and fibrils since it appears at a higher content in the fines fractions. Fiber activation via fiber split, removal of primary wall and surface defibrillation enhanced the affinity of the PCC for the fibrils. The laboratory handsheets prepared from the material demonstrated the importance of controlling the substrate fiber properties for the mineral-fiber composite, e.g. via refining, as differences between the refining levels and fractions were found to lead to differences in both optical properties and bonding. Graphic abstract

This study examines the effect of pulp type on the formability and elongation of paperboard, which are of key importance when producing 3D packages. Material performance was studied with a press-forming machine using laboratory handsheets as substrates. The handsheets were prepared from bleached softwood and hardwood kraft pulps, chemi-thermomechanical pulp, recycled newsprint, and mixtures of birch kraft and other pulps. The effect of microfibrillated cellulose (MFC) on substrate properties and material formability was also investigated. The 3D elongation of MFC-free handsheets varied between 1.2 and 5.5%. Depending on the pulp type and sheet composition, three essential sheet properties were recognized. These properties were bulk, elastic modulus and bending stiffness, the first two of which affect material bending stiffness. Sheets made from softwood fibers were superior to other samples, but their low bending stiffness resulted in distortion of formed trays. A partial replacement of birch kraft with recycled newsprint did not lead to a loss of sheet extensibility, which suggests that the interactions between the converting tools and the substrate have a great effect on material convertibility. Scanning electron micrographs showed that the pulp type affects the mechanism behind fracture initiation. The ability of MFC to increase extensibility was limited to mechanical pulps, indicating the important role of the main pulp component in defining tensile properties.

The effect of water-soluble anionic binders and a modified cationic-precipitated calcium carbonate layer-by-layer structure on dye ink spreading and absorption has been studied. The multilayered coating was alternately spray-coated onto the substrate in order to determine dye interdiffusion and specific interaction including solvent absorption behavior in the nano- and microporous layers. The amount of the hydrophilic binder in the top coating was varied in order to adjust the porosity and to determine the effect of electrostatic charge interaction and to adjust dye fixation. Cationic nano- and microporous coatings and particle assemblies were created by spray-coating with cationic calcium carbonate precipitated in the presence of PDADMAC. The deposition of dye on the various coatings revealed that a small amount of anionic binder in the top coating favoured the absorption and spreading of dye and solvent, whereas a higher binder dose closed the pores and reduced the dye fixation and rate of solvent absorption. Although the top layer is essential for dye retention, it was demonstrated that the multilayering is essential not only for dye setting and dye capturing mechanism but can be utilized for vertically controlling the dye penetration and retention in the formed hydrophilic gel complex, which has a significant influence on optical effects and mechanical durability.

Press forming process is an important manufacturing process to produce paperboard tray packages. During the press forming, sever deformation occurs at the intricate shapes that can cause localized strains and the fracture. The formability can be improved by the crease lines and controlling parameters. Creases reduce the confine stiffness and assist the folding of the paperboard into the complex shapes. In this paper, the press forming process is modelled and simulated with the aid of finite element method. We focus especially on control parameters such as blank-holding force, friction and the behavior of creases at different forming levels. A stress-based failure criterion is also designed and modelled to analyze the rupture. The FE-model consisted of the male die, female die, blank holder and paperboard blank. A commercial material with the grammage of 290 g/m 2 and thickness of 0.353mm is used in this study. The paperboard is modelled as an elastoplastic material and Hill’s yield criterion with isotropic hardening is used to interpret the hardening behavior. The creases are modelled as hinge connectors (one rotational degree of freedom). The failure criterion is implemented by the user-defined subroutine in Abaqus. In conclusion, the developed model can be used to analyze the crease behavior, strain mapping and the prediction of failure, which enables the better understanding of the paperboard converting in the press forming process.

In the original publication, the less than symbol () in Tables 2 and 4.

The aim of this study was to determine hydrothermally induced changes in the physico-chemical properties of a fine microfibrillated cellulose (MFC). The MFC was prepared from a monocomponent endoglucanase-treated never-dried birch kraft pulp which had been run several times through a microfluidizer in order to obtain a sample substantially free from fibers or fiber fragments. The fine MFC was subjected to hydrothermal treatment at $$150\,^{\circ }\hbox {C}$$ for 0.5, 2.5, 4.5, 8.5 and 20.5 h, after which the viscosity, water-retention capacity, surface charge, discoloration and formation of hydrolysis products were determined. The viscosity, surface charge and water-retention capacity of MFC decreased as a result of the treatment but in oscillatory measurements the storage and loss moduli increased. Hydrothermal treatment also caused discoloration of the sample which could not be fully washed away with water. Surface analysis with XPS revealed no significant changes in the surface structure of the dried MFC cakes but the filtrates after the hydrothermal treatment were complex mixtures of sugars, organic acids and furans. The main degradation products detected were xylose and xylobiose, but isomerization products of sugars (xylulose, fructose) were also found in the filtrates. In addition numerous organic acids, including formic, glycolic, lactic and xylonic acid, were identified in the filtrates, showing that both acid and alkaline catalyzed reactions occur due to dissociation of water into $$\hbox {H}^{+}$$ and $$\hbox {OH}^{-}$$ .

The material properties of substrates such as paperboard are normally measured under laboratory conditions but their physico-mechanical properties are likely to change during a press-forming process. A measurement device of has therefore been developed to obtain real-time data of paperboard tray production and a new insight into phenomena related to press forming and tool-substrate interaction. An existing mould set was modified for measurement of the forming force by replacing the male mould with a mould that included a set of force sensors. Detection of defects such as ruptures require the use of multiple force sensors that make it possible to obtain more detailed measurement data. To validate the performance of the device, a number of solid bleached paperboard (SBB) materials were selected to represent different kinds of coated paperboard structures in order to obtain a comprehensive general view of the phenomena occurring in the tray-pressing process. The friction coefficients of the test materials were measured by two different methods Force values obtained with the measurement device were used to calculate the friction coefficients and these were also obtained by a standard laboratory test method. The measurement device was also utilized to detect rupturing during the forming of the paperboard trays.

The convertibility of paperboard in a press-forming process was studied using a novel type of tool set that allows forming of small substrates such as laboratory handsheets (i.e. experimental materials) to investigate the role of mold design on substrate-press-tool interaction. The tool set makes it possible to prepare rectangular trays in both sliding and fixed blank modes in a pilot-scale press-forming machine. The tests showed that the fixed-blank mode makes it possible to estimate the elongation of the substrate in the forming process by determining the maximum forming depth for rupture-free samples. A more detailed inspection with an optical microscope of grid-patterned materials revealed that elongation took place mostly on the rim area in addition to the tray wall, and that the outer dimensions of the blank remained practically unchanged. The behavior of the material in press forming process was evaluated in addition to the novel tool set in a bigger, production-scale mold, and results showed good agreement between the small tool set and the standard mold, in spite of the dimensional differences. The smaller size of the mold did not require a compromise in any aspect of the press-forming process.

There is a wide range of materials that can be considered as nonwoven random networks of fibres. Such materials include glass-fibre mats, filters, various paper products and structural components of cells and tissues. The mechanical properties of these kinds of networks have been studied extensively for many decades. As many of such networks form more or less two-dimensional structures, they can, to a good approximation, be considered to consist of randomly distributed fibres or filaments connected at their crossings points. Recent development of the resolution of X-ray computed tomography have enabled imaging of the three dimensional structure of such materials with a resolution sufficient to produce accurate information of the fibre network. As the mean segment length, for given elastic properties of the fibers and contacts in the network, essentially affects the elastic response of the network, it is a property of great practical importance, but it has been very difficult to determine. We therefore introduce a method to determine in practice the mean segment length along with the density of fiber-fiber contacts.

Scanning probe microscopy (SPM) was used for studying the changes in topographical, chemical, thermal and electrostatic properties of a styrene-butadiene latex coating as a function of annealing time. Changes in local surface properties obtained with SPM were correlated with changes in surface chemistry measured by time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and contact angle measurements. The studied copolymer film goes through chemically and topographically meta-stable transition states during thermal annealing, reaching a steady state only after a significant annealing time (21 h). The differences in surface chemistry of the meta-stable states appeared as characteristic thermal and electrostatic properties of the latex coating. The results on film formation and drying are discussed in light of existing literature and theories. In this transition stage, the surface concentrations of polymeric components show unstable behavior, accordingly shifting the thermal transitions. Furthermore, the drying of the surface and desorption of surfactants is affecting the surface charge balance, changing from negative to positive. This was attributed to the change of balance of ionic components on the surface.

Electrostatic elds in the toner image transfer nip of laser printers were calculated by exact solution of the Poisson equations for a two-dimensional (2D) model and by applying for the paper the approximation of dielectric thickness. Both the distribution and location of the electric eld strength component parallel to the paper surface were investigated and eld values were calculated for different paper and toner parameters. The conditions of the occurrence of Paschen discharge in the toner image transfer nip were analysed.

The glass transition temperature ( T g ) for two latices with different styrene/butadiene compositions was determined by the thermal SPM probe resonance frequency method. The results were compared with the T g values obtained by differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), process rheometer (PR) and thermo-mechanical analyzer (TMA) measurements. The T g values detected by the thermal SPM method agreed well with the T g values obtained by DSC and calculated by the Fox–Flory equation. DMA, on the other hand, showed a significantly higher T g value for both latices than those obtained from theoretical calculations, the thermal SPM method and DSC. The T g obtained from the PR curve was slightly higher for the latex with a low styrene content, whereas good agreement was obtained with the thermal SPM data for the latex with a high styrene content. The glass transition temperature determined by TMA agreed fairly well with the thermal SPM data for the latex with the low styrene content, whilst the value of T g for the second latex was much less than those obtained by the other methods. The thermal SPM method detects changes in thermal behavior (thermal diffusivity, heat capacity) during heating of the latex films rather than changes in the mechanical properties. Information about the sample history could be seen in the thermal SPM curves, which was further associated with the degree of latex film formation, especially when the roughness of the films was taken into consideration.

This paper concerns the combined influences of high impaction rates and surface geometries on the spreading–absorption behaviour of Newtonian fluid droplets under non-equilibrium conditions. A volume of fluid method is used to simulate the motion of up to 50 μ m diameter droplets onto surfaces comprising protuberances below 12 μ m in width. On both flat and systematically arranged pyramidal surfaces, spreading is an exponential function of the maximum depth of absorption. Surface spreading is furthermore a linear function of the droplet Reynolds number and a simple method of predicting spreading from the Reynolds number has been identified herein. At high impact velocities, kinetic energy driven spreading dominates over wetting driven flow; though, its relativity to absorption is a function of the droplet pressure pulse. Lateral (plan view) spreading on irregular surfaces is found to be inversely proportional to surface roughness. In this paper, surface geometry is shown to be a critical determinant of both spreading and absorption and thereby, the research herein provides details that could be useful in functionalising surfaces. Finally, new surface roughness equations derived herein make the comparison of surface spreading to surface roughness more realistic than commonly used roughness factors such as the Wenzel and R a roughness.

Association between a sodium salt of a linear dodecylbenzene sulphonate and a non-ionic fatty alcohol ethoxylate surfactant during film formation of styrene/butadiene latex

Changes in the surface chemical properties of kaolin minerals may significantly affect the amounts of poly(vinyl alcohol) (PVOH) and its more hydrophobic analogue, partly hydrolysed polyvinyl acetate (PVOH/Ac), which are adsorbed. It is shown that pre-adsorbed anionic sodium polyacrylate (NaPA) and sodium hexametaphosphate (SHMP) dispersants increase the adsorbed amounts of both PVOH and PVOH/Ac. The mineralogical characteristics of the minerals were found to be even more important for the adsorption process, which is attributed to the larger amounts of PVOH/Ac adsorbed onto kaolin minerals with higher concentrations of montmorillonite contaminants (>1%). Very low affinity was found between the polymers and those kaolin minerals substantially free from montmorillonite. The low affinity of PVOH and PVOH/Ac for a silica surface strongly suggests that the silanol groups located on the basal plane of kaolin particles may not act as main anchor sites for the polymer. This strongly indicates that the non-ionic polymers have a great affinity for the ancillary montmorillonite mineral on the kaolin.

The influence of the latex surface chemistry on the association of latices with different cellulose derivatives has been investigated by means of isothermal calorimetry and electrophoresis. The chemistries of three grades of coating latices differed with regard to the type and amount of vinylic monomer and the level of carboxylation. In addition, a styrene/butadiene latex substantially free from surfactant was used to establish the influence of physically pre-adsorbed surfactants on the association with the cellulose derivatives sodium carboxymethylcellulose (NaCMC), hydroxyethylcellulose (HEC) and ethyl(hydroxyethyl)cellulose (EHEC). The results show that the latex chemistry, in terms of hydrophilic character originating from carboxylic acid groups, significantly affects the adsorption of the non-ionic HEC and EHEC. A higher degree of carboxylation or a more polar latex, such as vinyl acetate/acrylate, reduces the association with non-ionic cellulose derivatives. The addition of anionic sodium dodecylbenzene sulphonate or non-ionic fatty alcohol ethoxylate surfactants to the surfactant-free styrene/butadiene latex emulsion did not significantly change the association behaviour with EHEC, although it was evident that, for example, a sodium dodecyl sulphonate type of surfactant participated significantly in the adsorption process. Even if the surface polarity of the latex governs the association characteristics at the interface, the solubility properties of the cellulose derivatives must be considered, meaning that the hydrophobic character plays an important role in the associative interaction between the latex and cellulose derivatives in aqueous media.

The influence of aluminium and titanium dopants on the structure and properties of MCM-41 silica has been evaluated and compared with previously published results. The acidity and basicity of the surface states (adsorption sites) were of special interest. The total acidity was studied by using temperature-programmed ammonia desorption (NH3-TPD). Additionally, organic probe molecules with known Lewis and/or Brϕnsted acid or base functional groups were adsorbed on the powder samples in dry cyclohexane. Both UV–vis spectroscopy and microcalorimety were used to quantify the adsorption. The adsorption data of the monofunctional probes were fitted with Langmuir-, Freundlich- and Henry-corrected Langmuir isotherms providing both the number of the surface sites and strength of probe molecule adsorption. The surface charge densities, relating to Brϕnsted acidity and basicity, were determined for the doped samples in water using potentiometric titration. DRIFT spectroscopy was used to identify the type of the surface sites. The hexagonal pore structure of the doped MCM-41 samples was observed to remain roughly unaltered for all samples. The NH3-TPD analysis indicates that the acidity increases as a result of modification. The probe adsorption showed that the number of sites increases and the strength of adsorption enhances with surface modification. It seems that the simple Langmuir-isotherm is sufficient for the surface state analysis in most cases. In a few cases, the Freundlich- or the Henry-corrected Langmuir isotherm gave, however, a superior fit to the experimental surface excess data. The DRIFT-analysis confirmed the existence of Lewis sites and the formation of Brϕnsted type acid sites with enhanced Al- or Ti-doping, which was supported by the other methods used.

The interactions between highly cationic starch and likewise cationic calcite were investigated by determining the adsorption isotherms and the flocculation of the calcite dispersions at different concentrations of starch. Starch of varying degree of substitution (DS), 0.2, 0.35, and 0.5, and molecular weight (MW), ∼3800 and ∼2×106 g mol−1, were used. The experiments were in addition made at three different temperatures; 25, 35, and 45 °C. It was found that the interactions in most cases were of fairly low character. Consequently, the entropy and low solubility of the starch are expected to be the dominant driving forces for adsorption. The cationic character of both the untreated calcite and the starch generate an electrostatic repulsion that counteracts a possible adsorption. There is also repulsion between the cationic substituents in the starch, which among others factors controls the solubility of the starch in the aqueous phase. The repulsion can be affected by adding electrolytes. NaCl was used for this purpose in this investigation. As a result of the changes in the electrostatic repulsions the adsorbed amount of starch onto calcite did also change. The adsorption did increase with increasing NaCl concentrations, as did the degree of flocculation. The high MW starches did in all the conditions examined adsorb to a higher degree than did the low molecular ones. Increasing the temperature from 25 to 45 °C causes changes in the adsorption and flocculation behavior of the dispersions, especially in systems where starch with DS of 0.2 is present. The starches of higher charge are less affected by the temperature due to stronger internal repulsion. The low MW starches did not flocculate the calcite dispersions, while the starches of high MW initially flocculated the dispersions and restabilized them at higher concentrations. The high MW starch with DS 0.2 induced the strongest flocculation.

The role of stabilizing agents in the interaction between styrene/butadiene latex and calcium carbonate particles has been studied using isothermal titration calorimetry (ITC) and an electrokinetic sonic amplitude (ESA) technique. It is demonstrated that the polyacrylate sodium salt (dispersing agent, referred to as NaPA) used as stabilizing agent for the calcium carbonate suspensions principally affects the interfacial properties of the calcite surface. An electrostatic barrier is created and this decreases the attractive interactions between the latex and the negatively charged mineral surface. The total enthalpy change observed when an emulsion of styrene/butadiene particles substantially free from surfactant was added to the dispersed calcium carbonate could be described via a relatively complex path. The process included (i) an exothermic response from the association of the latex particles (adsorption process) with the dispersed calcium carbonate surface and (ii) an endothermic bulk phase effect due to the adsorption on the latex particles of dissolved species originating from the calcium carbonate. Stabilization of the latex particles with sodium dodecyl benzene sulfonate (SDBS) or a non-ionic fatty alcohol ethoxylate surfactant did not significantly change the enthalpy of interaction. It was further demonstrated that SDBS had a very weak affinity for the dispersed calcium carbonate particles and that dissolution of species, such as calcium ions, from the calcium carbonate surface, allows further adsorption of SDBS onto the latex particles.

Mechanisms of inkjet ink spreading and absorption on a coated paper have been studied using a polyelectrolyte multilayering technique. By applying alternating sequences of cationic and anionic polyelectrolyte layers on a mineral coated paper, the role of the interfacial chemistry was evaluated. The polyelectrolyte multilayer was created to imitate a thin resin-like liquid-absorptive layer and to clarify the role of the charge of the protruding polyelectrolyte layer on ink spreading and colorant fixation. The formation of a thin polyelectrolyte layer and coating coverage was confirmed by X-ray photoelectron spectroscopy (XPS). A submolecular mechanical imaging of the polyelectrolyte complexes with an atomic force microscope (AFM) revealed differences in modulus and different nanosize agglomerates were identified which were ascribed to polyion complexes. The polyelectrolyte coatings significantly affect the solid–liquid interaction and particularly the ink spreading revealed as intercolor bleeding and wicking. The interfacial interaction between the ink and the applied polyelectrolyte layers showed differences between dye- and pigment-based colorants, which could be emphasized by the polyelectrolyte chemistry.

High alkalinity in peroxide bleaching has traditionally been achieved using sodium hydroxide and sodium silicate. In the present work, partial and total substitution of traditional sodium-based peroxide bleaching auxiliary chemicals with a highly pure magnesium hydroxide-based bleaching additive was studied on two high-brightness mechanical pulp types from Norwegian spruce (Picea abies): pressure groundwood and thermomechanical pulp. Peroxide bleaching with 3.0% charge was carried out on both pulps to a given brightness level. The bleached pulp was studied with respect to electrical conductivity, zeta potential, and water retention value. The bleaching filtrate was measured for total organic carbon content, biological and chemical oxygen demand, cationic demand, extractives content, and turbidity. The main results from this study were that the cationic demand and electrical conductivity of the bleaching filtrate were significantly lowered for both pulps when a magnesium-based bleaching process was used. At the same time, the zeta potential of the dilute pulp suspension was only slightly affected. Magnesium hydroxide-based peroxide bleaching seems to increase the water retention value of the pulp, especially on fines-rich pressure groundwood, predicting a good strength potential of the pulp. The bleaching filtrate from the magnesium hydroxide-based process was significantly cleaner in all categories measured, which indicates that this is an environmentally sound concept.

The surface chemical and physical character of offset paper was studied before and after application of model fountain solutions based on isopropyl alcohol and an alcohol-free surfactant solution. The paper surface features were characterised with atomic force microscopy and the surface energies were determined by contact angle measurements. Changes in the surface chemical properties induced by the fountain solutions were investigated with X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. Coated papers wetted with the surfactant solution revealed a slight increase in the root mean square roughness, but the isopropyl alcohol solution led to no observable changes. The change in sub-micro roughness is ascribed not only to substrate swelling or migration of coating constituents but also to the presence of surfactant on the surface. A change in the surface energy and particularly the polar contribution was observed after application of the surfactant solution. The X-ray photoelectron spectroscopy showed an increase in the oxygen-to-carbon ratio, which confirms the presence of surfactant on the surface. Time-of-flight secondary ion mass spectroscopy showed that the isopropyl alcohol solution did not change the elemental composition of the surface whereas the surfactant solution clearly did so. The distribution of surfactant on the surface was confirmed by mapping the characteristic fragments of the molecule.

A novel method was developed for studying the ink-paper interface and the structural variations of a deposited layer of ink. Combining high-resolution x-ray tomography with laser ablation, the depth profile of ink (toner), i.e., its varying thickness, could be determined in a paper substrate. X-ray tomography was used to produce the 3D structure of paper with about 1 μm spatial resolution. Laser ablation combined with optical imaging was used to produce the 3D structure of the printed layer of ink on top of that paper with about 70 nm depth resolution. Ablation depth was calibrated with an optical profilometer. It can be concluded that a toner layer on a light-weight-coated paper substrate was strongly perturbed by protruding fibers of the base paper. Such fibers together with the surface topography of the base paper seem to be the major factors that control the leveling of toner and its penetration into a thinly coated paper substrate.

The flocculation performance of cationic starches on calcite pretreated with anionic sodium polyacrylate (NaPA) was investigated by measuring the mean particle size and the dynamic mobility of the calcite dispersions. Cationic starches of different molecular weight and degree of substitution were used. By varying the amount of anionic sodium polyacrylate, which has a strong affinity to the calcium carbonate surface, one is able to anionically modify the particles and reverse the charge character of the originally cationic calcium carbonate. By such modification of the charge character of the calcium carbonate dispersion, it is possible to approach the mechanisms of flocculation caused by cationic macromolecules like starch. The importance of different mechanisms of flocculation, such as bridging, charge neutralization, and flocculation induced by polyelectrolyte complexes (PEC), was further investigated in this work. It was found that when the NaPA is completely absorbed at the calcite surfaces the mechanism of the flocculation induced by the starch is mainly bridging flocculation. Excess NaPA in the calcium carbonate dispersion will result in polyelectrolyte complexes formed between the non-absorbed NaPA and the oppositely charged starch polymers. These complexes will in most cases strongly enhance the flocculation due to mainly charge neutralization. Depending on the ratio of non-absorbed NaPA and the starch in the aqueous phase, the calcite dispersion is either re-stabilized or more strongly flocculated due to the formed polyelectrolyte complexes. Both the mobility and the particle size measurements support the mechanisms described. It was further demonstrated that the molecular weight and degree of substitution of the starches might be adjusted to control the flocculation behavior.

The mechanisms of adsorption and association for sodium carboxymethylcellulose (NaCMC) in calcium carbonate suspensions have been determined from isothermal calorimetry and adsorption measurements. The equilibrium adsorption isotherms were determined by two different methods of separation; a depletion method and a serum exchange method. The enthalpy of dilution for NaCMC was determined on supernatants obtained from the calcium carbonate suspensions in order to investigate the interaction between NaCMC and dissolved species from the mineral. For comparison, NaCMC was injected into CaCl(2) solutions in order to determine the role of calcium ions in the adsorption process. The initial part of the adsorption isotherm showed a quasi-infinite slope indicating a high affinity for the NaCMC to the calcium carbonate surface, which was significantly reduced when anionic sodium polyacrylate was preadsorbed onto the calcium carbonate implying competitive adsorption. An endothermic enthalpy change was observed between the NaCMC and the calcium carbonate surface, suggesting attachment of the carboxylic acid groups onto the hydrated calcium sites. A similar endothermic enthalpy was observed when NaCMC was injected into CaCl(2) solutions or supernatants obtained from the calcium carbonate suspensions, indicating a complexation of carboxylic acid groups and hydrated calcium ions. It was concluded that the mechanisms of interaction of NaCMC in calcium carbonate suspensions are primarily an association between NaCMC and Lewis acid sites on the calcium carbonate surface and the formation of NaCMC-Ca(2+) complexes in the bulk solution, both of which will be affected by the amount of anionic sodium polyacrylate present.