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The adsorption of cationic polyelectrolytes (C-PAMs and PDACMAC) with different charge densities and molecular weights on silica and cellulose model surfaces was examined using a quartz crystal microbalance with dissipation, QCM-D. The conformation and viscoelastic properties of the adsorbed polyelectrolyte layers were studied by modelling the data with the Q-Tools program. When comparing the adsorption behavior on cellulose and silica a clear difference both in adsorption kinetics of polyelectrolytes and the viscoelastic properties of the formed polyelectrolyte film was observed. On cellulose the polyelectrolyte films were viscous and more dissipative at the beginning of the adsorption but when the adsorption proceeded the layers became more rigid and stiffer, in contrast to the behavior on silica.

The adsorption of laccases and ferulic acid on a lignin substrate has been studied using a quartz crystal microbalance with dissipation (QCM-D) and an atomic force microscope (AFM). Two different additional strategies were applied: ferulic acid was added after laccase pretreatment, or coadsorbed together with laccase. The effect of two laccases isolated from Trametes hirsuta and Melanocarpus albomyces was compared on lignin activation. The QCM-D results were also compared against bulk experiments on chemithermomechanical pulp. The two laccases affected the adsorption of ferulic acid differently. Adsorption of T. hirsuta laccase was not observed, while the adsorption of M. albomyces laccase was obvious. However, both laccases still activated lignin and the amount of ferulic acid adsorbed was significantly higher on laccase-activated lignin than on the non-activated one. Rinsing after activation removed some slightly bound laccase from the substrate and decreased the adsorbed amount of subsequently added ferulic acid. Interestingly, only T. hirsuta laccase could catalyse the lasting attachment of polymerised ferulic acid onto lignin. The QCM-D and AFM results correlated with the findings of studies concerning bonding of ferulic acid on chemithermomechanical pulp. Thus, this approach is useful in studying the behaviour of enzymes on lignin substrates.

The adsorption of polyelectrolyte (PE) multilayers and complexes, obtained from both high- and low-charge polyelectrolytes, was studied on silica and on cellulose model surfaces by quartz crystal microbalance with dissipation (QCM-D). The film properties acquired with the different strategies were compared. When polyelectrolytes were added on an oppositely charged surface in sequence to form multilayers both the change in frequency and dissipation increased. The changes in frequency and dissipation were clearly higher if low-charge PEs were used in the multilayer formation. The substrate, silica or cellulose, did not affect the adsorption behaviour of low-charge PEs and only minor differences were seen in the adsorbed amounts and changes in dissipation of high-charge PEs between SiO2 and cellulose. The complexes formed by low-charge PEs had higher changes in frequency and dissipation at low ionic strength on both surfaces, while the complexes formed from high-charge polyelectrolytes adsorbed more at high salt concentration. The complexes of low-charge polyelectrolytes adsorbed more on silica, while the complexes formed by high-charge PEs formed thicker layers on cellulose. The charge ratio had a significant effect on the adsorption and the highest changes in frequency and dissipation were obtained in the anionic/cationic charge ratio of 0.5–0.6. Generally, the multilayers and complexes formed by low-charge polyacrylamides adsorbed highly and formed rather thick layers on both surfaces, unlike the high-charge PEs which formed thin layers using either one of the addition techniques.

A method of preparing model cellulose surfaces by the Langmuir–Blodgett (LB) technique with horizontal dipping procedure has been developed. The primary aim for the use of these surfaces was adsorption studies performed with the quartz crystal microbalance with dissipation (QCM-D) instrument. Hydrophobised cellulose (trimethylsilyl cellulose, TMSC) was deposited on the hydrophobic, polystyrene-coated QCM-D crystal. After 15 dipping cycles, the TMSC film fully covers the crystal surface. TMSC can easily be hydrolysed back to cellulose with acid hydrolysis. With this method a smooth, rigid, thin and reproducible cellulose film was obtained. Its morphology, coverage, chemical composition and wetting was further characterised using atomic force microscopy (AFM), X-Ray photoelectron spectroscopy (XPS), and contact angle measurements. The swelling behaviour and the stability of the cellulose film in aqueous solutions at different ionic strengths were studied using the QCM-D instrument. The swelling/deswelling properties of the cellulose film were those expected of polyelectrolytes with low charge density; some swelling occurred in pure water and the swelling decreased when the ionic strength was increased. No significant layer softening was detected during the swelling. The effect of electrolyte concentration and polymer charge density on the adsorption of cationic polyelectrolytes on the cellulose surface was also investigated. At low electrolyte concentration less of the highly charged PDADMAC was adsorbed as compared to low charged C-PAM. The adsorbed amount of PDADMAC increased with increasing ionic strength and a more compact layer was formed while the effect of electrolyte concentration on the adsorption of C-PAM was not as pronounced.

The atomic force microscope (AFM) colloidal probe technique has been used to investigate forces between cellulose beads as well as cellulose beads and mica in aqueous solution, and the interaction between cellulose surfaces in xylan solutions. Several observations of the behaviour of the cellulose beads were made. Swelling of the beads in aqueous solutions is rather slow. Thus, it is important to let the beads equilibrate before measurements. The beads are somewhat compressed when forced together to constant compliance, but relax back to their original shape in a few minutes. A long-range electrostatic repulsion between cellulose and mica occurs on approach. The xylan concentration in solution affects the forces between two cellulose surfaces. When the concentration increases from 10-100 mg/I more xylan adsorbs slowly and irreversibly on the cellulose leading to an increasingly long-range and stronger repulsion between the surfaces on approach. Adhesion between the layers is very low and seems to be due to entanglement of polymer chains. Studies of the adsorption of xylan (100 mg/1) on cellulose films with a quartz crystal microbalance with dissipation (QCM-D) verify that a thick, water-swollen layer of xylan is formed by slow adsorption. It has been proposed that adsorbed xylan on fibre surfaces increases paper strength. We conclude that this must be associated with the behaviour of the adsorbed layers of xylan on drying.

Depth profiling of the chemical composition of paper and paper coatings is of essential importance for the development of paper qualities tailored to the demands set by recycling and new printing technologies. In this work the chemical composition of biodegradable, starch-based paper coatings was investigated by Fourier transform photoacoustic spectroscopy (FTIR/PAS). The coatings were prepared by mixing solutions of cationised starch and anionic surfactant (sodium oleate) and were applied in thicknesses ranging from 20 to 60 μm. FTIR/PAS spectra were recorded using step-scan phase modulation, and the spectral information was processed using photoacoustic (PA) magnitude/phase spectra calculations and generalised two-dimensional (G2D) spectral correlation analysis. Variation of the phase modulation frequencies made it possible to differentiate the characteristic bands arising from the base paper and the coating layer. Closer study of the coating spectra showed, however, that the position of the carbonyl salt band of sodium oleate is influenced by the environment, i.e., the position of band is different in pure oleate, oleate mixed with starch and oleate-starch mixture in contact with the calcium carbonate-containing base paper. On the basis of this information, the specific depth profile of the coating layer was obtained by analysis of magnitude spectra, phase angles and a G2D correlation spectrum. Each of these approaches indicated that the long chain surfactant (sodium oleate) is enriched in the outermost surface layer of the coating. In the attempt to calculate the thickness of the coating layer from the phase data, the overlapping of the signals did not allow the traditional equation to be used as such and a new baseline correction method was introduced to eliminate the overlapping. The advantage of this method is that no measurements of pure components are required. However, the method can be applied only for well-resolved and linearly overlapped bands. FTIR/PAS is concluded to yield a completely new type of qualitative information, which can be utilised in the development of paper coatings.

This thesis presents studies of the interactions between suspended particles and dissolved and colloidal substances (DCS) in process water. The main focus has been to determine if colloidal wood resin is adsorbed by suspended fines or fillers, and how the dissolved material influences this adsorption. The effect of some synthetic polymers on this adsorption has also been investigated.Successive refining of mainly Norway spruce followed Successive refining of mainly Norway spruce followed by removal of the produced fines after each refining stage, resulted in fines with different physical and chemical properties. In the first refining stage mainly flake-like fines were produced, while more fibrillar fines were produced in later refining stages. The different types of fines were analysed for both the bulk and the surface composition. Variation in the chemical composition between the fines was particularly striking with regard to the surface composition. Special attention was also given to the amount and origin of charged groups since these may consume cationic additives in the papermaking process. After alkali treatment, between 80 and 90% of all the charged groups measured by polymer adsorption originated from three uronic acids.Fines were shown to adsorb model colloidal wood resin, but the adsorption was greatly influenced by the pH or salt content. Also the amount of dissolved components in the suspension, which sterically stabilised the colloidal wood resin, was shown to strongly influence the adsorption of the colloidal wood resin to the fines. The flake-like fines adsorbed the colloidal wood resin to a higher extent than the fibrillar fines. This selectivity was also possible to obtain by using polyethyleneoxide (PEO). PEO removed the sterically stabilised colloidal wood resin more efficiently when flake-like fines rather than fibrillar fines were present. For comparison, cationic polyacrylamide (CPAM) did not have this selectivity. The selectivity of PEO was explained by a higher affinity to flake-like fines than fibrillar fines. It was shown that more PEO adsorbed to flake-like fines rather than to fibrillar ones. PEO may adsorb to extractive surfaces, but was inhibited by adsorbed components from the dissolved fraction. The degree of stabilisation was also shown to influence the adsorption of the colloidal wood resin by other particles like fillers. This adsorption, which was energetically favourable, did not occur at high concentrations of dissolved material.