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The use of paper dry strength additives is one of the methods for producing packaging boards with a lower grammage while maintaining mechanical properties. In the present work, papers were formed using dissolving grade kraft fibres, kraft fibres and carboxymethylated cellulose (CMC) modified kraft fibres (C-kraft fibres), with either cationic starch (CS), anionic polyacrylamide (APAM) or anionic polyelectrolyte complexes (PECs). Fibres and sheets were characterized to evaluate how the saturation adsorption of the different strength additives influences the properties of the treated fibres and the final handsheets. The tensile index of papers made from C-kraft fibres was the highest due to the highest adsorption capacity of strength additives. Moreover, the strength additives increased the tensile index by 33–84 %, while z-directional tensile strength was increased dramatically by 46–139 %. Bending stiffness was improved by 2.6–25 %, and the combination of CS and APAM or PECs resulted in a significant improvement in bending stiffness compared to the addition of CS alone. Importantly, the strength improvement did not sacrifice the density significantly. In summary, the knowledge gained from the current study expands the understanding of strength additives and their relationship with fibres of different surface charge and the overall paper properties. [ABSTRACT FROM AUTHOR]

Light-weight paper products that contain less fibres, but with a maintained bulk and improved strength properties, are highly desirable due to the low cost of raw materials and improved logistics of packaged goods. In this respect, the adsorption capacity of dry strength additives onto fibres, which is affected by the surface charge of said fibres, is very important for the development of these mechanically robust paper products. The influence of the surface charge on the adsorption of strength additives was investigated for, dissolving grade fibres, kraft fibres and kraft fibres modified with carboxymethyl cellulose (CMC) with different surface charge densities, but the same fibre dimensions. The strength additives investigated were cationic starch (CS), anionic polyacrylamide (APAM) and polyelectrolyte complexes (PECs), containing CS and APAM. A linear relationship was found between the surface charge of the fibres and the saturated adsorbed amount of CS. However, when either APAM or PECs adsorbed as secondary layers onto the CS, no correlation between cellulose charge and the saturation adsorption could be observed. The adsorption of APAM was dramatically affected by the pre-adsorbed amount of CS, whereas PECs were less influenced. Moreover, the additives improved the tensile strength (60%) and strain at break (> 100%) of handsheets formed with the kraft fibres and adsorbed APAM. It was also found that CS/APAM increased the sheet density while CS/PECs lowered it. In conclusion, the gained fundamental understanding of these adsorption of additives is of significant importance to facilitate the industrial development of sustainable low-cost high-end packaging products. [ABSTRACT FROM AUTHOR]

Contact-active antibacterial materials with irreversibly attached antibacterial agents have been developed as an environmentally friendly alternative to traditional biocide treatments. Of particular interest are materials fabricated through the physical adsorption of charged polymers. This simple method allows for the use of water-based processes and materials originating from renewable sources, e.g., cellulosic fibres. Furthermore, by varying the process parameters, such as ionic strength, it is possible to tune the properties of the adsorbed polymer layer. However, the underlying antibacterial mechanism remains obscure, and this hinders the rational design of antibacterial multilayers. To gain further insight into the antibacterial mechanisms of physically adsorbed multilayers of polyvinylamine and polyacrylic acid, the surface charge of cellulose fibres was increased via radical oxidation. This oxidation increased the amount of polymer that was adsorbed and resulted in increased antibacterial efficacy against both Escherichia coli and Bacillus subtilis compared with polymer-modified unoxidised fibres. Electron microscopy analysis of the E. coli adhered to the fibres revealed that the multilayer treatment resulted in elongated bacteria with deformed cell walls. This work demonstrates the importance of electrostatic interaction to the antibacterial effect of polymer-modified fibres . [ABSTRACT FROM AUTHOR]

Polyelectrolytes have been used extensively in the papermaking industry for various purposes. Although recent studies have shown that polyamines can be efficient dry-strength additives, the mechanism governing the strength enhancement of paper materials following the adsorption of polyamines onto pulp fibres is still not well understood. In this study, the effect of the adsorption of polyallylamine hydrochloride (PAH) onto the surface of unbleached kraft pulp fibres was investigated on both the fibre and the network scale. Isolated fibre crosses were mechanically tested to evaluate the impact of the chemical additive on the interfibre joint strength on the microscopic scale and the effect was compared with that previously observed on the paper sheet scale. X-ray microtomography was used to understand structural changes in the fibrous network following the adsorption of a polyamine such as PAH. Using image analysis methods, it was possible to determine the number of interfibre contacts (or joints) per unit length of fibre as well as the average interfibre joint contact area. The results showed that the median interfibre joint strength increased by 18 % upon adsorption of PAH. This can be achieved both by a larger molecular contact area in the contact zones and by a stronger molecular adhesion. The addition of the polymer also increased the number of efficient interfibre contacts per sheet volume. This combination of effects is the reason why polyamines such as PAH can increase the dry tensile strength of paper materials. [ABSTRACT FROM AUTHOR]

A new, robust method for measuring the average pore size of water-swollen, cellulose I rich fibres is presented. This method is based on the results of solid-state NMR, which measures the specific surface area (area/solids mass) of water-swollen samples, and of the fibre saturation point (FSP) method, which measures the pore volume (water mass/solids mass) of water-swollen samples. These results are suitable to combine since they are both recorded on water-swollen fibres in excess water, and neither requires the assumption of any particular pore geometry. The new method was used for three model samples and reasonable average pore size measurements were obtained for all of them. The structural characterization of water-swollen samples was compared with the dry structure of fibres as revealed using BET nitrogen gas adsorption after a liquid exchange procedure and careful drying. It was concluded that the structure of the water-swollen fibres sets an upper limit on what is obtainable in the dry state. [ABSTRACT FROM AUTHOR]

The polymerization of the pre-formed hydrophilic block followed by the chain extension with a hydrophobic monomer in water and the final formation and adsorption of nanolatexes onto surfaces with a 2D or 3D distribution of charged groups. [Display omitted] It is theoretically predicted and hypothesized that the charge density and size of spherical nanoparticles are the key factors for their adsorption onto oppositely charged surfaces. It is also hypothesized that the morphology and charge of the surface are of great importance. In-plane 2D (silica) or a volumetric 3D (regenerated TEMPO-oxidized cellulose model surfaces) distribution of charged groups is expected to influence charge compensation and, thus, the adsorption behavior. In this work, self-stabilized nanolatexes with a range of cationic charge densities and sizes were synthesized through reversible addition − fragmentation chain-transfer (RAFT) polymerization coupled with polymerization-induced self-assembly (PISA). Their adsorption onto silica and anionic cellulose model surfaces was investigated using stagnation point adsorption reflectometry (SPAR) and quartz crystal microbalance with dissipation (QCM-D). Experiments and theory agree and show that the size of the nanolatex and the difference in charge density compared to the substrate determine the charge compensation and, thus, the surface coverage. Highly charged or large nanolatexes overcompensate the surface charge of non-porous substrates leading to a significant repulsive zone where other particles cannot adsorb. For porous substrates like cellulose, the vertical distribution of charged groups in the 3D volume prevents overcompensation and thus increases the adsorption. This systematic study investigates the isolated effect of surface charge and size and paves the way for on-demand particles specifically designed for a surface with particular characteristics. [ABSTRACT FROM AUTHOR]

Cationic polyelectrolytes (polyallylamine and polyvinylamine with different molecular masses) were adsorbed onto lignocellulosic fibres from unbleached and unbeaten spruce chemical fibres with different kappa numbers to investigate the effects on the mechanical properties of the final paper materials. Adsorption isotherms were first established to determine the maximum quantity of polymer that could be adsorbed onto each type of fibre. Paper sheets were then made with different amounts of added polyelectrolyte, and the structural and mechanical properties of the sheets were investigated, as well as the effect of an extra heating. The use of fibres with different kappa numbers led to different responses in terms of adsorption, and thus to differences in the mechanical properties of the resulting sheets. The tensile strength index was significantly increased (almost 50 % improvement in the best case) as a consequence of this polyelectrolyte adsorption onto the fibres, even at as low an adsorption level as 2 mg/g. The heating of paper sheets for 10 min at 160 °C was also shown to improve the tensile strength index by about 10 % for pulps with high kappa number. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of two types of cationic polyacrylamides in the presence of a background electrolyte was studied on substrates including silicon oxide, kraft pulp fibres and thin films of regenerated cellulose. One of the polyelectrolytes was a conventional cationic polyacrylamide (MeCPAM) and the other was a benzyl-containing derivative of cationic polyacrylamide (BzCPAM). It was found that the aromatic substituents of BzCPAM strongly enhanced the adsorption on substrates of hydrophobically modified silicon oxide when a background electrolyte was present. A similar effect was also seen in the case of BzCPAM adsorption on unbleached pulp fibres, but in this case MeCPAM also exhibited a strong adsorption at high background electrolyte concentrations. On bleached pulp fibres, BzCPAM maintained a high adsorption up to a concentration of 100mM NaCl whereas MeCPAM adsorption showed a significant decrease at this salt concentration. On model cellulose films, the adsorption of BzCPAM was similar to that of MeCPAM and the non-ionic interactions with cellulose appeared weak, since there was no adsorption of either polyelectrolyte in 300mM NaCl. [Copyright &y& Elsevier]

Cationic polyallylamine (PAH), was adsorbed onto lignocellulosic fibres, and a fluorescent label on the polyelectrolyte enabled its location to be shown by confocal fluorescence microscopy. The adsorption time and ionic strength were varied to study their effect on the localisation of the adsorbed PAH. The microscopy showed that a long adsorption time, 24 h, and a high ionic strength, 10−1 M NaCl + 5 × 10−3 M NaHCO3 or higher, resulted in the adsorption of polyallylamine throughout the fibre walls. Shorter adsorption times and/or lower ionic strength resulted in adsorption only to the fibre exterior. By preparing sheets from fibres with polyelectrolyte adsorbed either to the exterior parts or into the fibre cell wall and testing their mechanical behaviour, a link was established between the localisation of adsorbed polyelectrolyte and the mechanical properties. Adsorption to the fibre exterior led to an increase in tensile strength and strain at break. The creep deformation at 90%RH was also slightly reduced by the adsorption of low molecular weight PAH (15 kDa). When polyallylamine was adsorbed throughout the wall of the lignocellulosic fibres, the mechanical properties were not however improved and the creep deformation at 90%RH actually increased somewhat. [ABSTRACT FROM AUTHOR]

Abstract: The conformation of cationic polyelectrolytes preadsorbed on macroscopic silica surfaces was studied before and after addition of colloidal silica (CS) and compared to the fixation capacity of CS. The study included two polyelectrolytes of equal charge density, cationic polyacrylamide and cationic dextran. Adsorbed amounts were determined with stagnation point adsorption reflectometry (SPAR) and quartz crystal microgravimetry (QCM). Unsaturated layers of polyelectrolyte were formed in SPAR by stopping the adsorption at a fractional coverage relative to saturation adsorption. These layers were probed by secondary saturation adsorption of colloidal silica (CS). At low salt concentrations a high fractional coverage of polyelectrolyte was required to attain adsorption of CS, while significant adsorption of CS was found also for low fractional coverages of polyelectrolyte at salt concentrations above 10 mM NaCl. Saturation adsorption of cationic polyacrylamide (CPAM) and cationic dextran (Cdextran) onto the silica surface was found to be similar, while the secondary adsorption of CS was significantly higher onto preadsorbed CPAM compared with Cdextran. The QCM and SPAR data together indicated that the adsorbed layer of Cdextran was thinner than CPAM, and that a loose, expanded layer was formed after adsorption of CS on CPAM but not on Cdextran. [Copyright &y& Elsevier]

Abstract: The electrostatic interaction between quarternised hyperbranched polymers (polyesteramides) and a silicon oxide (SiO2) surface has been studied via adsorption studies with quartz crystal microbalance instrument with dissipation (QCM-D). Frequency shift (Δf) results show that the increase in both pH and salt concentration positively affect the adsorbed amount of these polymers, calculated by Sauerbrey equation, on the QCM crystal. The adsorbed amount of HA1 (with lower molecular weight and higher charge density) was lower than that of HA2 (with higher molecular weight and lower charge density) in all experiments. It was also observed that there are no significant changes in the dissipation after adsorption of these polymers. This indicated that both hyperbranched polymers formed rigid adsorbed layers on the negative SiO2 surface. Additionally, the results were compared with adsorption of poly-DADMAC and the results showed that the hyperbranched polymers formed thicker and more rigid layers as compared with the poly-DADMAC. [Copyright &y& Elsevier]

By measuring adsorption using a stagnation point reflectometer, it was shown that multilayers consisting of cationic polymers and dissolved and colloidal material released from wood fibres into process waters are formed on an anionic silica surface. The similarity of this experiment to the papermaking process was established.It was established using the “JKR-method” that this multilayer adsorption had a profound effect on the adhesion, in air, of an elastic polydimethyl siloxane (PDMS) probe to these surfaces. The adhesion of PDMS to a bare silica surface showed a large hysteresis, with a much stronger adhesion measured upon the separation of the two surfaces compared with the value obtained from gradually pressing them together. It was suggested that this hysteresis was due to specific interactions (hydrogen bonding) that develop over time. The first adsorbed layer, a cationic poly(dimethyldiallylammoniumchloride) (polyDMDAAC), decreased the magnitude of the hysteresis and gave a relatively low adhesion, which may be due to the fact that these specific interactions were blocked. The subsequent build up of layers of lipophilic wood extractives in the form of colloidal particles and cationic polymer increased the adhesion. This was interpreted as being due to the build up of a soft layer on the stiff mineral surface causing additional energy dissipation upon separation, even though the molecular adhesion was still decreased compared with the bare silica. This was supported by the fact that none of the individual components of the multilayer increased the adhesion when applied in a relatively thin layer on the silica, and by the fact that a thick deposition of cast coated wood extractives gave a very high adhesion. Stearic acid was chosen as a model substance for extractives and deposited onto silica from vapour phase. This resulted in a partial coverage of the surface where the stearic acid was present as patches of different size. This gave a significant reduction of the adhesion. The solid stearic acid melted and was redistributed when confined between the PDMS and the silica. This gave a thinner and more uniform layer. The application of a “monolayer” of C18-tails covalently bound to the silica by siloxane links, gave a very significant reduction of the magnitude of the adhesion hystersis. It is concluded that the distribution of the contaminants over the surface is very significant for the adhesion properties.This is relevant to practical papermaking with respect to: (i) the build up of deposits on process equipment and its effect on adhesion to these surfaces; (ii) fibre–fibre adhesion and thereby paper strength, a phenomenon that can never be studied without directly measuring the adhesion, which makes specific solutions to the practical problems possible. [Copyright &y& Elsevier]

The adsorption of cationic polyacrylamide and silica nanoparticle systems onto a model surface has been compared with the adsorption and flocculation of a fiber suspension. An increase in ionic strength affects the polyelectrolyte adsorption in different ways in these two systems. With a silica surface, an increase in the ionic strength leads to a continuous increase in the adsorption. On a cellulose fiber, the adsorption increases at low ionic strength (1–10 mM NaCl) and then decreases at higher ionic strength (10–100 mM NaCl). When polyelectrolyte is added to the fiber suspension, flocculation occurs with an optimum around a polyelectrolyte addition of 0.4 mg g−1. Above this addition level the flocculation effect is reduced and dispersion occurs when more than 1.2 mg g−1 polyelectrolyte is added. This behavior suggests a bridging flocculation, the dispersion being explained by electrosteric stabilization of the suspension. Addition of silica nanoparticles to the fiber suspension leads to a greater degree of flocculation than in a single polyelectrolyte system. The adsorption of nanoparticles to a polyelectrolyte-covered silica surface increases both the adsorbed amount and the thickness of the adsorbed film. A more extended silica particle, giving a more extended polyelectrolyte–silica film, also results in a higher degree of fiber flocculation. [Copyright &y& Elsevier]

The adsorption of nonionic polymers to cellulose is of large importance both in the plant cell wall during synthesis and for the development of sustainable materials from wood. Here, the thermodynamics of adsorption of the polysaccharide xyloglucan (XG) to both native and chemically modified cellulose with carboxyl groups was investigated using molecular dynamics simulations. The free energy of adsorption was calculated as the potential of mean force between an XG oligomer and model cellulose surfaces in a range of temperatures from 298 K to 360 K. It was found that the adsorption near room temperature is an endothermic process dominated by the entropy of released interfacial water molecules. This was corroborated by quantitative assessment of the absolute entropy per water molecule both at the interface and in the bulk. In the case of native cellulose, the adsorption became exothermic at higher temperatures, while the relatively strong interactions between water and the charged groups of the oxidized cellulose impede such a transition. The results also indicate that the extraction of strongly associated hemicelluloses would be facilitated by low temperature. [ABSTRACT FROM AUTHOR]

Abstract: Paper is a versatile material with obvious advantages in being both inexpensive and environment friendly. However, a major drawback compared with many other materials, such as plastics, is that it is sensitive to both liquid water and moist air. Traditionally paper is protected from liquid water by sizing. The present work presents a new way to make paper water resistant by combining the layer-by-layer (LbL) technique with the adsorption of a colloidal wax onto the multilayer structure. After the adsorption of five layers of poly(allylamine hydrochloride) and poly(acrylic acid) followed by the adsorption of 8mg paraffin wax per gram fibre, the contact angle measured 60s after a drop of water was applied to the sheet was about 138°. If the sheets were cured for 30min at 160°C after sheet making, the contact angle was ca. 150°. The heat treatment of sheets prepared from LbL-modified fibres without the addition of wax gave a contact angle of about 113°. To decouple structural effects from changes in surface energy upon heat treatment of PAH/PAA LbL films, model experiments were carried out where LbL assemblies were prepared on silicon oxide and cellulose model surfaces. The contact angle increased when these films were heat treated but it did not exceed 90°. The reason for this is due to the lack of structure of the model surfaces on a micrometre scale. The adsorption of wax impaired the mechanical properties of paper sheets made from modified fibres compared to sheets from the LbL-modified fibres. However, at an adsorption of 8mg paraffin wax per gram fibre there was still an increase by 37±1% in tensile strength index compared to the untreated reference pulp (33.8±0.7 and 24.7±0.6kNm/kg respectively). [Copyright &y& Elsevier]

Abstract: The influence of mixing procedure on the properties of polyelectrolyte complexes (PECs) was investigated using two complexation techniques, polyelectrolyte titration and jet mixing, the latter being a new method for PEC preparation. For the low-molecular-weight polyelectrolytes polyacrylic acid (PAA) and polyallyl amine hydrochloride (PAH), shorter mixing times produced smaller PECs, whereas for higher molecular weights of the same polyelectrolytes, PEC size first decreased with decreasing mixing time to a certain level, after which it started increasing again. This pattern was likely due to the diffusion-controlled formation of “pre-complexes”, which, in the case of low-molecular-weight polymers, occurs sufficiently quickly to form stable complexes; when polyelectrolytes are larger, however, non-equilibrium pre-complexes, more prone to aggregation, are formed. Comparing the techniques revealed that jet mixing produced smaller complexes, allowing PEC size to be controlled by mixing time, which was not the case with polyelectrolyte titration. Higher polyelectrolyte concentration during jet mixing led to the formation of larger PECs. It was also demonstrated that PEC size could be changed after preparation: increasing the pH of the PEC dispersion led to an irreversible increase in PEC size, whereas lowering the pH did not influence PEC size. The adsorption behavior of PECs formed from weak polyelectrolytes on model substrates was studied using QCM-D, SPAR, and AFM imaging; the results indicated that increasing the pH increased the amount of PECs adsorbed to model surfaces. However, the amount of PECs adsorbed to the model surfaces was low compared with other systems in all studied cases. [ABSTRACT FROM AUTHOR]

Abstract: The build-up of multilayers constructed from polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA) under different pH conditions was continuously monitored using the quartz crystal microbalance with dissipation. The adsorbed amount of polymer as well as the amount of coupled water was determined. Furthermore, from dissipation measurements, it was possible to determine the visco-elastic properties of the adsorbed multilayer. These properties were highly dependent on the polyelectrolyte present in the outermost layer. The multilayer was far more rigid and elastic with PAA as the outermost layer. Furthermore, a link has been established between the conformability or rigidity of a multilayer covered surface and the adhesion between such surfaces. Adhesion measurements using the atomic force microscope showed a greater pull-off force when the more viscous PAH was present in the outermost layer. [Copyright &y& Elsevier]

The temperature-dependence of xyloglucan (XG) adsorption onto smooth cellulose model films regenerated from N-methylmorpholine N-oxide (NMMO) was investigated using surface plasmon resonance spectroscopy, and it was found that the adsorbed amount increased with increasing temperature. This implies that the adsorption of XG to NMMO-regenerated cellulose is endothermic and supports the hypothesis that the adsorption of XG onto cellulose is an entropy-driven process. We suggest that XG adsorption is mainly driven by the release of water molecules from the highly hydrated cellulose surfaces and from the XG molecules, rather than through hydrogen bonding and van der Waals forces as previously suggested. To test this hypothesis, the adsorption of XG onto cellulose was studied using cellulose films with different morphologies prepared from cellulose nanocrystals (CNC), semicrystalline NMMO-regenerated cellulose, and amorphous cellulose regenerated from lithium chloride/dimethylacetamide. The total amount of high molecular weight xyloglucan (XGHMW) adsorbed was studied by quartz crystal microbalance and reflectometry measurements, and it was found that the adsorption was greatest on the amorphous cellulose followed by the CNC and NMMO-regenerated cellulose films. There was a significant correlation between the cellulose dry film thickness and the adsorbed XG amount, indicating that XG penetrated into the films. There was also a correlation between the swelling of the films and the adsorbed amounts and conformation of XG, which further strengthened the conclusion that the water content and the subsequent release of the water upon adsorption are important components of the adsorption process. [ABSTRACT FROM AUTHOR]

This work focuses on adsorption of polyions onto oppositely charged surfaces and on responses to the addition of a simple monovalent salt as well as to the polyion length (degree of polymerization). We also discuss possible mechanisms underlying observed differences, of the adsorbed amount on silica surfaces at high pH, between seemingly similar polyions. This involves theoretical modeling, utilizing classical polymer density functional theory (DFT). We furthermore investigate how long- and short-chain versions of the polymer adsorb onto carboxymethylated cellulose, carrying a high negative charge. Interestingly enough, comparing results obtained for the two different surfaces, we observe an opposite qualitative response for the molecular weight. The large polymer adsorbs more strongly at a silica surface, but for cellulose at low salt levels, there are indications that the trend is opposite. Another difference is the very slow adsorption process observed for cellulose, particularly with short polymers; in fact, with short polymers, we were sometimes unable to establish any adsorption plateau at all. We speculate that the slow dynamics is due to a gradual diffusion of short polymers into the cellulose matrix. This phenomenon could also explain why short-chain polymers seem to adsorb more strongly than long-chain ones, at low salt concentrations, provided that the latter then are too large to enter the cellulose pores. Cellulose swelling at high salt concentrations might diminish these differences, leading to more similar adsorbed amounts or even a lower adsorption for short chains. [ABSTRACT FROM AUTHOR]

Abstract: In this study, thermo-responsive nanofibrillated cellulose (NFC) has been produced by the adsorption of thermo-responsive polyelectrolytes to the NFC. Three block copolymers were synthesized in which the polyelectrolyte block was composed of quaternized poly(2-(dimethylamino)ethyl methacrylate) (qPDMAEMA) and the thermo-responsive block was composed of poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA). The block copolymers were synthesized employing atom transfer radical polymerization (ATRP) and the PDMAEMA block was utilized as a macroinitiator for the polymerizations of PDEGMA. The length and charge of the PDMAEMA block were kept constant in all three block copolymers, while three different molecular weights of the PDEGMA block was synthesized. The PDMAEMA block was quaternized to introduce positive charges and the block copolymers were subsequently adsorbed onto the negatively charged NFC that was dispersed in water. The lower critical solution temperatures (LCSTs) of the free block copolymers in solution were analyzed by dynamic light scattering (DLS). The composites were analyzed by QCM-D, FT-IR and TGA, which clearly showed an adsorption of the block copolymer onto the NFC. The grafted NFC showed a thermo-responsive behavior in solution upon heating and cooling, thus supporting that the properties of the polyelectrolyte can be transferred to the cellulose. By this methodology, thermo-responsive NFC materials can be produced in a straight-forward manner in water dispersions, without performing any chemical reactions on the NFC. [Copyright &y& Elsevier]

Abstract: In this study, particle polyelectrolyte complexes (PPECs) were formed by mixing cationic polyacrylamide (CPAM) and silica nanoparticles using the jet mixing technique. Within certain limits, the size of the formed PPECs could be controlled. The aim was to prepare PPECs with embedded sacrificial bonds, similar to those found in bones. Examination of PPEC adsorption to silica model surfaces indicated that smaller PPECs adsorbed to a higher level than larger ones, due to the higher diffusion speed of smaller complexes. Adsorption studies of the same components as in the PPECs, but arranged in multilayers, that is, particle polyelectrolyte multilayers (PPEMs), indicated a stable, gradual build-up of material on the surface with smaller nanoparticles, whereas PPEMs comprising elongated nanoparticles appeared to be more loosely adsorbed onto the surface when the nanoparticles were in the outer layer, due to repulsive forces within the adsorbed layer. The AFM colloidal probe technique was used to study the interaction between surfaces treated with PPECs, multilayers, or polyelectrolyte complexes (PECs). The results showed that the expected long-range disentanglement could be achieved with PPECs but that the pull-off forces were generally low. Treatment with PPEMs comprising the same polymer and nanoparticle components produced higher pull-off values, together with disentanglement behaviour, possibly due to better contact between the surfaces. Adhesion experiments with polymer PECs showed significantly higher pull-off values than with the PPECs, probably due to polymer interdiffusion across the surface boundary. [Copyright &y& Elsevier]

Abstract: In this work, the objective was to synthesize a compatibilizer that can electrostatically adsorb onto cellulose fibers, in fiber-based composites, to enhance the interaction between the fibers and non-polar polymer matrices. This physical route to attach the compatibilizer onto and thereby modify a fiber surface is convenient since it can be performed in water under mild conditions. Polystyrene (PS) was used for the high molecular weight, non-polar, block and poly(dimethylamino)ethyl methacrylate (PDMAEMA) was used as the polar block, which was subsequently quaternized to obtain cationic charges. The block copolymer self-assembles in water into cationic micelles and the adsorption to both silicon oxide surfaces and cellulose model surfaces was studied. The micelles spread out on the surface after heat treatment and contact angle measurements showed that the contact angles against water increased significantly after this treatment. AFM force measurements were performed with a PS probe to study the adhesive properties. The adhesion increased with increasing contact time for the treated surfaces, probably due to entanglements between the polystyrene blocks at the treated surface and the probe. This demonstrates that the use of this type of amphiphilic block copolymer is a promising route to improve the compatibility between charged reinforcing materials, such as cellulose-based fibers/fibrils, and hydrophobic matrices in composite materials. [Copyright &y& Elsevier]

Abstract: Wet and dry adhesion between dextran-coated surfaces were measured aiming to understand the influence of polymer compatibility. The wet adhesion measurements were performed using the atomic force microscope (AFM) colloidal probe technique whereas the dry adhesion measurements were performed using the micro adhesion measurement apparatus (MAMA). Two types of dextrans were used, one cationically modified dextran (DEX) and one that was both cationically and hydrophobically modified (HDEX), leading to three different combinations of polymer-coated surfaces; (1) DEX:DEX, (2) HDEX:DEX, and (3) HDEX:HDEX. DEX increased dry adhesion more than HDEX did, which likely is due to differences in the ability to form specific interactions, especially hydrogen bonding. HDEX gave strong wet adhesion, probably due to its poorer solvency, while DEX contributed to reducing the wet adhesion due to its hydrophilicity. All combinations showed a steric repulsion on approach in aqueous media. Furthermore, when HDEX was adsorbed on either or both surfaces a long range attractive force between the surfaces was detected outside this steric regime. [Copyright &y& Elsevier]

The adsorption of carboxymethylcellulose (CMC) on cellulose surfaces is of relevance from both academic and industrial perspectives as it facilitates resource-efficient modification of cellulose fibres that allows them to carry negative charges. It is known that, compared to monovalent ions, Ca2+ ions are superior ions in facilitating CMC adsorption and the subsequent introduction of charge on cellulose fibres. However, the formation and deposition of calcium oxide involved in this process necessitates the search for alternative cations. Magnesium ions form one of the more promising candidates since they are already used in the pulping process to prevent cellulose degradation during peroxide bleaching. This work aims at elucidating the effects of the industrially relevant alkaline earth metal divalent cations Mg2+ and Ca2+ on the CMC adsorption process onto cellulose surfaces. Quartz Crystal Microbalance (QCM-D) technology was used to follow the adsorption in model systems in real time, whereas the adsorption of CMC on commercial fibres was studied using polyelectrolyte titrations, total organic carbon (TOC) analysis and conductometric titrations. This study shows that the presence of Ca2+ ions was more favourable for the adsorption of CMC to both types of cellulosic surfaces than Mg2+ ions. The distinction in the adsorption behaviour in the presence of Mg2+ and Ca2+ is suggested to be due to the differences in the polarizability of the ions. The findings are decisive in designing efficient industrial processes for the adsorption of polyelectrolytes to cellulose surfaces of similar charge. [Display omitted] [ABSTRACT FROM AUTHOR]

• Anionic PEDOT:PSS adsorbs spontaneously on anionically charged cellulose. • Temperature-dependent QCM-D suggests the larger entropic contribution to adsorption. • Low pH, high ionic strength and multivalent counterions favor PEDOT:PSS adsorption on CNF. • PEDOT:PSS and CNF show higher adhesion at low pH in colloidal probe measurements. • PEDOT:PSS organizes differently on 3D and 2D cellulose surfaces. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a conducting polymer frequently used with cellulose, to develop advanced electronic materials. To understand the fundamental interactions between cellulose and PEDOT:PSS, a quartz crystal microbalance with dissipation (QCM-D) was used to study the adsorption of PEDOT:PSS onto model films of cellulose-nanofibrils (CNFs) and regenerated cellulose. The results show that PEDOT:PSS adsorbs spontaneously onto anionically charged cellulose wherein the adsorbed amount can be tuned by altering solution parameters such as pH, ionic strength and counterion to the charges on the CNF. Temperature-dependent QCM-D studies indicate that an entropy gain is the driving force for adsorption, as the adsorbed amount of PEDOT:PSS increased with increasing temperature. Colloidal probe AFM, in accordance with QCM-D results, also showed an increased adhesion between cellulose and PEDOT:PSS at low pH. AFM images show bead-like PEDOT:PSS particles on CNF surfaces, while no such organization was observed on the regenerated cellulose surfaces. This work provides insight into the interaction of PEDOT:PSS/cellulose that will aid in the design of sustainable electronic devices. [ABSTRACT FROM AUTHOR]