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This study covers a green method to prepare hybrid lignocellulosic nanopapers by combining wood nanofibres (WNFs) and cellulose nanofibres (CNFs). The WNFs and CNFs behave synergistically to compensate for the drawbacks of each other resulting in enhanced hybrid nanopapers. The draining time of hybrid nanopapers was improved by up to 75% over CNF nanopaper, and the mechanical properties, modulus, strength and elongation, were respectively improved up to 35%, 90% and 180% over WNF nanopaper. Additionally, the water resistance of hybrid nanopapers was considerably improved with a water contact angle of 95°; the neat CNF nanopaper had a contact angle of 52°. The morphology of nanopapers, studied by electron microscopy, indicated that lignin acts as a matrix, which binds the nanofibres together and makes them impervious to external environmental factors, such as high humidity. The reported hybrid nanopapers are 100% bio-based, prepared by a simple and environmentally friendly processing route. Reported hybrid nanopapers can be used in novel applications such as gas barrier membranes and printable electronics.

Biomaterials of different nature have been and are widely studied for various biomedical applications. In many cases, biomaterial assemblies are designed to mimic biological systems. Although biomaterials have been thoroughly characterized in many aspects, not much quantitative information on the molecular level interactions between different biomaterials is available. That information is very important, on the one hand, to understand the properties of biological systems and, on the other hand, to develop new composite biomaterials for special applications. This work presents a systematic, quantitative analysis of self- and cross-interactions between films of collagen I (Col I), collagen IV (Col IV), laminin (LN-521), and cellulose nanofibrils (CNF), that is, biomaterials of different nature and structure that either exist in biological systems (e.g., extracellular matrices) or have shown potential for 3D cell culture and tissue engineering. Direct surface forces and adhesion between biomaterials-coated spherical micro-particles and flat substrates were measured in phosphate-buffered saline using an atomic force microscope and the colloidal probe technique. Different methods (Langmuir-Schaefer deposition, spin-coating, or adsorption) were applied to completely coat the flat substrates and the spherical micro particles with homogeneous biomaterial films. The adhesion between biomaterials films increased with the time that the films were kept in contact. The strongest adhesion was observed between Col IV films, and between Col IV and LN-521 films after 30 s contact time. In contrast, low adhesion was measured between CNF films, as well as between CNF and LN-521 films. Nevertheless, a good adhesion between CNF and collagen films (especially Col I) was observed. These results increase our understanding of the structure of biological systems and can support the design of new matrices or scaffolds where different biomaterials are combined for diverse biological or medical applications.

Protection from liquid water and UV radiation are equally important, and a sophisticated approach is needed when developing surface coatings that preserve the natural and well-appreciated aesthetic appearance of wood. In order to prevent degradation and prolong the service life of timber, a protective coating was assembled using carnauba wax particles and zinc oxide nanoparticles via layer-by-layer deposition in water. For this purpose, a facile sonication route was developed to produce aqueous wax dispersion without any surfactants or stabilizers. The suspension was stable above pH 4 due to the electrostatic repulsion between the negatively charged wax particles. The particle size could be controlled by the initial wax concentration with average particle sizes ranging from 260 to 360 nm for 1 and 10 g/L, respectively. The deposition of wax particles onto the surface of spruce wood introduced additional roughness to the wood surface at micron level, while zinc oxide provided nano roughness and UV-absorbing properties. In addition to making wood superhydrophobic, this novel multilayer coating enhanced the natural moisture buffering capability of spruce. Moreover, wood surfaces prepared in this fashion showed a significant reduction in color change after exposure to UV light. A degradation of the wax through photocatalytic activity of the ZnO particles was measured by FTIR, indicating that further studies are required to achieve long-term stability. Nevertheless, the developed coating showed a unique combination of superhydrophobicity and excellent moisture buffering ability and some UV protection, all achieved using an environmentally friendly coating process, which is beneficial to retain the natural appearance of wood and improve indoor air quality and comfort.

Lignocellulosics, i.e., cellulose, lignin and hemicelluloses, are natural renewable polymers of high technological interest. The properties of products based on these polymers are largely determined by the forces at their interfaces. This review summarizes the main findings related to surface interactions relevant for papermaking and describes how the interest in novel, high performance renewable materials has changed the focus of the research to nanocellulosic materials. Areas of interest that need further work are also outlined.

A scalable tubular flow reactor was designed and developed for the continuous formation of colloidal lignin particles (CLPs). The reactor consists of a series of tubes, inside which many static mixing elements are equipped to aid in the formation of a homogeneous dispersion of CLPs. The colloids were formed instantaneously through self-assembly upon the addition of the lignin solution into water. The effects of flowrate, length of the tubes and static mixing elements on the particle size, stability and CLP yield after drying were determined. It was found that a higher flowrate of lignin solution within the testing range of 32-240 mL/min resulted in smaller sized CLPs. Optimizations of the mixing length and the static mixing elements to 3 m and at least 1 m, respectively, could ensure an efficient mixing, thus resulting in CLP dispersions with smaller size of lignin particles (200 nm – 400 nm) and high lignin concentrations (up to 2.8 wt. %) along with yields up to 95 %. The TEM images indicated that the formed colloids are composed of lignin particles of regular sphere shape and with good stability. The tubular reactor offers better control of particle size which ensures the formation of colloidal dispersions with narrower particle size distribution in comparison to a stirred mixer reactor. Furthermore, using a tubular reactor enables the continuous production of CLPs, making it suitable for scale up and industrial applications.

All-polysaccharide composite films were prepared from native, unmodified cellulose nanofibrils (CNF) mixed with various natural water-soluble polysaccharides like carboxymethyl cellulose, galactoglucomannan, xyloglucan and guar gum. Composite films were manufactured by pressurized filtration and hot pressing. The mechanical properties of the films were systematically evaluated in the dry and the wet state. GG was furthermore selectively oxidized using galactose oxidase (EC 1.1.3.9), and the effect of the degree of oxidation on the final composite film properties was shown. It was found that all the tested polysaccharides increased the strength and toughness of the dry composite films at 2 weight percent (wt.%) addition to CNF. After soaking the samples for 24 h in water, striking differences between the samples were found: already at 2 wt.% CMC the wet strength of the composite films diminished, while the uncharged polysaccharides improved the wet strength. For example, the addition of 2 wt.% GGM increased Young's modulus by a factor of 1.3, the tensile strength by a factor of 2.8, and the toughness by a factor of 3.4. The results are discussed in relation to the amount of water absorbed in the films and possible reasons for the improved properties are suggested.

Nanofibrillated cellulose (NFC) and hemicelluloses have shown to be highly promising renewable components both as barrier materials and in novel biocomposites. However, the hydrophilic nature of these materials restricts their use in some applications. In this work, the usability of modified O-acetyl galactoglucomannan (GGM) for modification of NFC surface properties was studied. Four GGM-block-structured, amphiphilic derivatives were synthesized using either fatty acids or polydimethylsiloxane as hydrophobic tails. The adsorption of these GGM derivatives was consecutively examined in aqueous solution using a quartz crystal microbalance with dissipation monitoring (QCM-D). It was found that the hydrophobic tails did not hinder adsorption of the GGM derivatives to cellulose, which was concluded to be due to the presence of the native GGM-block with high affinity to cellulose. The layer properties of the adsorbed block-co-polymers were discussed and evaluated. Self-standing NFC films were further prepared and coated with the GGM derivatives and the effect of the surface modification on wetting properties and oxygen permeability (OP) of the modified films was assessed.

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.

The purpose of this work was to better understand the effect polyelectrolyte complexes have on the interactions in cellulosic systems. The surface forces between cellulose spheres immersed in solutions of positively charged polyelectrolyte complexes, formed by cationic and anionic polyacrylamides, were studied using an atomic force microscope. The effect of the molecular weight and the charge density of the polyelectrolytes, as well as the background electrolyte concentration were investigated. The adsorption of the polyelectrolyte complexes on the negatively charged cellulose surface had a strong influence on the interactions between the surfaces and the forces were clearly different as compared to the single polymer systems. The interactions between the adsorbed polyelectrolyte complex layers were mainly steric and repulsive, even at low polymer concentrations. The comparison between two polyelectrolyte complexes showed that the complex formed by high molecular weight and low charged polyelectrolytes induced a steric force ranging further than the one induced by the complex formed by low molecular weight and high charged polyelectrolytes. Also the pull-off forces measured on separation ranged longer in the former case but the pull-off force was weaker. The fact that the interaction forces are totally different using polymer complexes as compared to single polymer systems can have a drastic effect on, e.g. water removal efficiency, as well as flocculation during the formation of the paper web.

Precipitated wood extractives were detected on cellulose fibres using a combined atomic force microscope (AFM) and confocal Raman microscope. With this combination of techniques, morphological and chemical information were obtained from the same sample location. For the first time unambiguous proof of the chemical structures of different morphological regions in the AFM phase contrast image was obtained.

The wetting behaviour and the morphology of lignin on cellulose fibres and mica in the presence of cationic polyelectrolytes have been studied. Lignin was adsorbed from aqueous solution on the surfaces of mica and cellulose fibres. Static contact angles and residual drop volumes were measured on modified surfaces over time. Surface morphology was examined by AFM. Both the structure of the adsorbed layer as well as the hydrophobicity depended on the polymer addition strategy. Lignin adsorbed as granules on both smooth and rough cationised surfaces. Adsorbed and organised lignin was capable of weakening the adhesion of water to both nonporous and porous hydrophilic substrates. Maximum contact angles were found when the adsorbed lignin layer formed a granular structure. In contrast, polymer/lignin complexes that were formed in solution and then adsorbed on mica or cellulose were not as effective in lowering the adhesion of water. They adsorbed on mica and pulp fibres as either a thin film or as larger blobs, depending on the properties of the cationic polymer.

The surface chemistry and morphology of spruce (Picea abies) mechanical pulps have been investigated by Electron spectroscopy for chemical analysis (ESCA) and Atomic force microscopy (AFM). As determined by ESCA, the content of lignin was slightly higher on the pulp surface than in the whole pulp. The surface coverage by lignin remained approximately the same after peroxide and dithionite bleaching, whereas on the ozone treated pressure groundwood (PGW) pulp the amount of lignin was strongly reduced. The AFM studies showed that the surfaces of mechanical pulp fibres are very heterogeneous, i.e. different cell wall layers are exposed along the fibre surface. It was found that the surfaces of unbleached PGW and thermomechanical pulp (TMP) fibres consist of both granular and fibrillar structures, whereas the surfaces of unbleached chemithermomechanical pulp (CTMP) fibres are almost fully covered by granular material. This granular layer, which is interpreted to originate from the middle lamella and the primary wall, was removed from the CTMP fibre surface after peroxide bleaching, exposing the underlying structure. However, the surface coverage by lignin determined by ESCA was not reduced. This suggests that peroxide bleaching of sulphonated CTMP pulp in some way modifies the lignin and pectin rich surface and that lignin occurs also in a non-granular form on the surface of mechanical pulps. Peroxide or dithionite bleaching had no effect on the morphology of PGW and TMP fibres. The highest amounts of extractives were found on unwashed and unbleached TMP pulp. It turned out that only part of the extractives was removed from the surface by alkaline treatment and by peroxide bleaching.

The forces between xylan-coated mica surfaces at pH 10 have been studied using the interferometric surface force apparatus. Xylan is a polysaccharide that is composed of (1,4)-linked beta -D-xylopyranose units, which are partially substituted at C2 with 4-O-methyl-alpha -D-glucuronic acid units and at C3 with alpha -L-arabinosyl units. Two different xylans were studied, one with 0.5% and one with 9% of the segments containing a carboxylic acid group. It was found that both xylans adsorbed onto the negatively charged mica surface despite their negative charge. The interactions between the xylan-coated surfaces were dependent on the charge density of the polymer. The xylan with higher charge density adsorbed in a more extended conformation leading to more long-range repulsion. The shapes of the force curves were consistent with the forces expected for anchored polyelectrolyte brushes. After compression the length of the protruding chains decreased. An increase in background electrolyte concentration led to a decrease in the range of the repulsion. This effect was, as expected, more pronounced for the high charge density xylan. In the presence of CaCl2 not only the long-range forces but also the layer thickness at high compressive load decreased.