The use of wood-derived cellulose nanofibrils (CNFs) or galactoglucomannans (GGM) for emulsion stabilization may be a way to obtain new environmentally friendly emulsifiers. Both have previously been shown to act as emulsifiers, offering physical, and in the case of GGM, oxidative stability to the emulsions. Oil-in-water emulsions were prepared using highly charged (1352 ± 5 µmol/g) CNFs prepared by TEMPO-mediated oxidation, or a coarser commercial CNF, less charged (≈ 70 µmol/g) quality (Exilva forte), and the physical emulsion stability was evaluated by use of droplet size distributions, micrographs and visual appearance. The highly charged, finely fibrillated CNFs stabilized the emulsions more effectively than the coarser, lower charged CNFs, probably due to higher electrostatic repulsions between the fibrils, and a higher surface coverage of the oil droplets due to thinner fibrils. At a constant CNF/oil ratio, the lowest CNF and oil concentration of 0.01 wt % CNFs and 5 wt % oil gave the most stable emulsion, with good stability toward coalescence, but not towards creaming. GGM (0.5 or 1.0 wt %) stabilized emulsions (5 wt % oil) showed no creaming behavior, but a clear bimodal distribution with some destabilization over the storage time of 1 month. Combinations of CNFs and GGM for stabilization of emulsions with 5 wt % oil, provided good stability towards creaming and a slower emulsion destabilization than for GGM alone. GGM could also improve the stability towards oxidation by delaying the initiation of lipid oxidation. Use of CNFs and combinations of GGM and CNFs can thus be away to obtain stable emulsions, such as mayonnaise and beverage emulsions. © 2021, The Author(s).

Abstract: Cellulose nanofibrils (CNFs) have been proposed for use in low-fat food products due to their availability and excellent viscosifying and gel forming abilities. As the CNFs are negatively charged, the presence of other components in foods, such as electrolytes and food additives such as xanthan gum is likely to affect their rheological properties. Hence, the study of these interactions can contribute valuable information of the suitability of CNFs as rheology modifiers and fat replacers. Rheological measurements on aqueous dispersions of TEMPO-oxidized CNFs were performed with variations in concentration of CNFs, concentration of electrolytes and with varying CNF/xanthan ratios. UV–Vis Spectroscopy was used to evaluate the onset of CNF flocculation/aggregation in the presence of electrolytes. The CNF dispersions followed a power-law dependency for viscosity and moduli on CNF concentration. Low electrolyte additions strengthened the CNF network by allowing for stronger interactions, while higher additions led to fibril aggregation, and loss of viscosity, especially under shear. The CNF/xanthan ratio, as well as the presence of electrolytes were shown to be key factors in determining whether the viscosity and storage modulus of CNF dispersions increased or decreased when xanthan was added. Graphical abstract: [Figure not available: see fulltext.].

Crosslinking-aided gelation was utilized to prepare hydrogels from softwood polysaccharides, with spruce galactoglucomannans (GGM)—a group of largely unexploited hemicelluloses—as the main component, aiming at conversion into sponge-like aerogels. Cellulose nanofibrils were used for the formation of a reinforcing network, which was further crosslinked together with a GGM matrix by ammonium zirconium carbonate, an inorganic salt that is regarded as safe for use in food packaging. The hydrogels were freeze-dried into stiff, low-density aerogels with 98 % of their volume composed of air-filled pores. When immersed in water, the aerogels absorbed water up to 37 times their initial weight, demonstrating elasticity and repeatable and reversible sponge capacity. The developed concept reassembles the wood polysaccharides in a new way, creating interesting possibilities for utilizing the abundant “green gold,” GGM. The obtained biobased materials could find application potential, for example, in the field of food packaging and could contribute in the reduction of the usage of petroleum-based plastics in the future.

The enzymatic hydrolysability of three industrial pulps, five lab made pulps, and one microcrystalline cellulose powder was assessed using commercial cellulolytic enzymes. To gain insight into the factors that influence the hydrolysability, a thorough characterization of the samples was done, including their chemical properties (cellulose content, hemicellulose content, lignin content, and kappa number), their macromolecular properties (peak molar mass, number-average molar mass, weight-average molar mass, polydispersity, and limiting viscosity) and their supramolecular properties (fibre saturation point, specific surface area, average pore size, and crystallinity). The hydrolysability was assessed by determination of initial conversion rate and final conversion yield, with conversion yield defined as the amount of glucose in solution per unit of glucose in the substrate. Multivariate data analysis revealed that for the investigated samples the conversion of cellulose to glucose was mainly dependent on the supramolecular properties, such as specific surface area and average pore size. The molar mass distribution, the crystallinity, and the lignin content of the pulps had no significant effect on the hydrolysability of the investigated samples.

Cellulose nanofibrils based on wood pulp fibres are most promising for biomedical applications. Bacterial cellulose has been suggested for some medical applications and is presently used as wound dressing. However, cost-efficient processes for mass production of bacterial cellulose are lacking. Hence, fibrillation of cellulose wood fibres is most interesting, as the cellulose nanofibrils can efficiently be produced in large quantities. However, the utilization of cellulose nanofibrils from wood requires a thorough verification of its biocompatibility, especially with fibroblast cells which are important in regenerative tissue and particularly in wound healing. The cellulose nanofibril structures used in this study were based on Eucalyptus and Pinus radiata pulp fibres. The nanofibrillated materials were manufactured using a homogenizer without pre-treatment and with 2,2,6,6-tetramethylpiperidine-1-oxy radical as pre-treatment, thus yielding nanofibrils low and high level of anionic charge, respectively. From these materials, two types of nanofibril-based structures were formed; (1) thin and dense structures and (2) open and porous structures. Cytotoxicity tests were applied on the samples, which demonstrated that the nanofibrils do not exert acute toxic phenomena on the tested fibroblast cells (3T3 cells). The cell membrane, cell mitochondrial activity and the DNA proliferation remained unchanged during the tests, which involved direct and indirect contact between the nano-structured materials and the 3T3 cells. Some samples were modified using the crosslinking agent polyethyleneimine (PEI) or the surfactant cetyl trimethylammonium bromide (CTAB). The sample modified with CTAB showed a clear toxic behaviour, having negative effects on cell survival, viability and proliferation. CTAB is an antimicrobial component, and thus this result was as expected. The sample crosslinked with PEI also had a significant reduction in cell viability indicating a reduction in DNA proliferation. We conclude that the neat cellulose nanostructured materials tested in this study are not toxic against fibroblasts cells. This is most important as nano-structured materials based on nanofibrils from wood pulp fibres are promising as substrate for regenerative medicine and wound healing.

The growing demand for sustainable products has spurred research into renewable materials, with cellulose-based materials emerging as prominent candidates due to their exceptional properties, abundance, and wide-ranging applications. In this context, there is a need to develop a better fundamental understanding of cellulose interactions such that we can continue to design and improve sustainable materials. Individual interactions can be difficult to assess in bulk fibre-based materials and therefore cellulose model materials have become indispensable tools for researchers as they can facilitate the study of cellulose interactions at a molecular level enabling the design of sustainable materials with enhanced properties. This study presents a new methodology for studying the effects of surface treatments on the individual fibre–fibre joint strength using wet-spun cellulose nanofiber (CNF) filaments as model materials. The Layer-by-Layer assembly technique is used to modify the surface chemistry of the model materials as well as bleached and unbleached hardwood Kraft fibres, demonstrating its potential to enhance adhesive properties and overall mechanical performance of papers made from these fibres. The study further explores the impact of increasing network density through wet-pressing during paper preparation, showcasing a comprehensive approach to molecularly tailor fibre-based materials to achieve superior mechanical properties. The proposed methodology provides a time-efficient evaluation of chemical additives in paper preparation.

The preparation of carboxymethylated microfibrillated cellulose (MFC) films by dispersion-casting from aqueous dispersions and by surface coating on base papers is described. The oxygen permeability of MFC films were studied at different relative humidity (RH). At low RH (0%), the MFC films showed very low oxygen permeability as compared with films prepared from plasticized starch, whey protein and arabinoxylan and values in the same range as that of conventional synthetic films, e.g., ethylene vinyl alcohol. At higher RH’s, the oxygen permeability increased exponentially, presumably due to the plasticizing and swelling of the carboxymethylated nanofibers by water molecules. The effect of moisture on the barrier and mechanical properties of the films was further studied using water vapor sorption isotherms and by humidity scans in dynamic mechanical analysis. The influences of the degree of nanofibrillation/dispersion on the microstructure and optical properties of the films were evaluated by field-emission scanning electron microscopy (FE-SEM) and light transmittance measurements, respectively. FE-SEM micrographs showed that the MFC films consisted of randomly assembled nanofibers with a thickness of 5-10 nm, although some larger aggregates were also formed. The use of MFC as surface coating on various base papers considerably reduced the air permeability. Environmental scanning electron microscopy (E-SEM) micrographs indicated that the MFC layer reduced sheet porosity, i.e., the dense structure formed by the nanofibers resulted in superior oil barrier properties.

The aim of this study is to design a nanocellulose based barrier film. For this purpose, cellulose nanofibrils (CNFs) are used as a matrix to create an entangled nanoporous network that is filled with two different nanofillers: nanoclay (reference), i.e. the mineral montmorillonite (MMT) and the bio-based TEMPO-oxidized cellulose nanocrystal (CNC-T), to produce different types of nanocelluloses and their main physical and chemical features were assessed. As expected, films based on neat CNFs exhibit good mechanical performance and excellent barrier properties at low moisture content. The introduction of 32.5 wt% of either nanofiller results in a significant improvement of barrier properties at high moisture content. Finally, thermal treatment of a dried CNF/CNC-T film results in a decrease of the oxygen permeability even at high moisture content (>70 %). This is mainly attributed to the hornification of nanocellulose. A key result of this study is that the oxygen permeability of an all-nanocellulose film in 85 % relative humidity (RH), is similar to CNF film with mineral nanoclay (MMT), i.e. 2.1 instead of 1.7 cm3 µm m−2 day−1 kPa−1, respectively.

There are limited methods available for measurement of the porosity of cellulose fibers, even more so for obtaining a pore size distribution. Conventional pore analysis methods require dry samples, with intact pores. However, pores in cellulose fibers collapse when dried from water and thus present a challenge for sample analysis. Furthermore, the pore collapse is partially irreversible which should be accounted for in the analysis. In this study, analysis of pore structure was carried out in the wet state with thermoporometry and also for critical point dried samples, analyzed with N2 sorption. This study determines the effect of fiber lignin content and certain spinning parameters on the pore size distribution of spun fibers before and after drying. It could also be concluded that solvent exchange, drying from a non-polar solvent will result in an altered pore size distribution, with a total pore volume greater than if dried from water, however not representative of the never-dried state. It is concluded that thermoporometry together with the water retention value (WRV) measurement is a powerful combination to acquire insights to the pore size distribution of spun fiber. 

Calculations of Hamaker constants using Lifshitz theory require the availability of accurate dielectric data, especially in the visible-ultraviolet region. We present spectroscopic ellipsometry data on well defined cellulose films of a limited thickness range (100–140 layers) deposited on an oxidised and hydrophobised silicon substrate. The spectral data, representing measurements from a perpendicular orientation to the fibre deposition direction, was used for estimates of the necessary spectral parameters, i.e. the oscillator strengths and characteristic frequencies in the UV-range. Our calculations show that cellulose has a relatively low Hamaker constant in air (58 zJ) and water (8.0 zJ). The implications for the surface energy estimates of cellulose and colloidal interactions between cellulose and various types of fillers and coating colours were discussed.

The aim of this study is to present the design, optimization and modelling of a chemical recovery system for a novel CS2-free viscose-type process that entails dissolution of pre-treated dissolving pulp in a continuous-flow reactor in cold alkali and wet spinning of cellulose in sodium carbonate solutions. Technologies already known to other industries for the recovery and reuse of chemicals, such as causticizing, recalcination, recarbonization and freeze-separation, were used. Chemical equilibria simulations were performed with OLI Studio 9.5, with the purpose to select experimental conditions which avoid undesired precipitations in each unit operation. Synthetic solutions mimicking the spent coagulation liquor were used in the laboratorial experiments. The proposed chemical recovery system was shown to be technically feasible and reduce chemical make-ups to a minimum of 45 kg/ton of NaOH and 4 kg/ton of H2SO4. Small amounts of Zn are expected to precipitate during recarbonization of the coagulation liquor at 30 °C and causticizing at 98 °C. Thus, a filter for ZnO particles should be included in the design of the recarbonization unit and a continuous purge of lime mud and input of fresh lime make-up should be needed to keep burnt lime availability at an acceptable level. Overall, the results presented in this study portray a solution to reduce operating costs and the environmental impact of novel viscose-type processes with alkaline spin dopes and wet spinning of cellulose in sodium carbonate solutions. © 2020, The Author(s).

The energy demand to produce cellulose nanofibrils, CNFs, is high and additionally the cost of the starting material, the pulp, is substantial as high purity cellulose dissolving pulp is generally used. Pulps aimed for board and paper are produced at higher yield as they contain hemicelluloses and, in the case of unbleached pulp, lignin, and would be a more economical starting material for CNFs. It is of interest to understand how the presence of hemicellulose and lignin affects the fibrillation process and CNF properties. Kraft cooks of softwood were performed as well as kraft cooks with addition of polysulfide to increase the hemicellulose content. Part of the pulps were bleached to remove residual lignin, thus making it possible to compare pulps with and without lignin. Higher amount of hemicellulose had an obstructive effect on the enzymatic pre-treatment whereas lignin had no adverse effect on enzyme accessibility. Increased amount of charged groups improved the accessibility for enzymes. Both hemicellulose and lignin were carboxymethylated when pre-treatment by carboxymethylation was employed. However, carboxymethylation partly dissolved hemicelluloses. The tensile strength of CNF films was independent of the chemical composition of the pulp and the pre-treatment strategy. However, since the enzymatic pre-treatment decreased the cellulose DP more, CNF films from enzymatically pre-treated pulps had generally lower tensile strength. © 2022, The Author(s).

The effect of initial stages of pulping of spruce, resembling prehydrolysis and alkaline cooking was studied using CP/MAS 13C-NMR, X-ray scattering, FSP and carbohydrate composition in order to study the impact of the pre-treatments on the fiber wall nanostructure. Removal of fiber wall components, hemicellulose and lignin, increased the fiber wall porosity and induced cellulose fibril aggregation. The effect of temperature and pH in the treatment on cellulose fibril aggregate size appears to be secondary. It is the removal of hemicellulose that has a profound effect on the supramolecular structure of the cellulose fiber wall. As the amount of hemicellulose dissolved from wood increases, the fibril aggregate size determined by NMR increases as well, ranging from 16 to 28 nm. Specifically, a good correlation between the amount of glucomannan in the fiber wall and the fibril aggregate size is seen. The lower the amount of glucomannan, the larger the aggregate size. Glucomannan thus seems to prevent aggregation as it acts as a very efficient spacer between fibrils. Elemental fibril size determined by NMR, was quite similar for all samples, ranging from 3.6 to 4.1 nm. By combining measurement methods, a more well-resolved picture of the structural changes occurring during was obtained. © 2021, The Author(s).

The hypothesis was that low residual alkali after cooking would cause lignin re-precipitation during washing and in turn affect the subsequent oxygen delignification stage negatively. To test the hypothesis, kraft cooks were performed in lab-scale to different residual alkali levels, ranging from 5 to 15 g/L and the pulps were subjected to washing with either water or 0.1 M NaOH and then oxygen delignified. The results show that even at low residual alkali and washing with water, the pH in the liquor after washing was above 11 which is sufficiently high to keep lignin in solution. No effect of residual alkali level was observed on the performance of the oxygen delignification stage. 

Most of our knowledge on kraft pulping comes from studies on dissolved lignin in the freely drainable black liquor and isolated residual lignin in pulp. However, entrapped liquor in the delignified chips has been shown to differ significantly from the free liquor. The present study has compared three liquor fractions: free, lumen and fiber wall liquor. The free liquor was obtained by draining the delignified chips, the lumen liquor was separated by centrifugation and the fiber wall liquor by subsequent leaching. The liquor in the fiber wall had the lowest concentration of lignin and hydrosulfide ions and the highest concentration of monovalent cations. The dissolved lignin in the fiber wall liquor had the highest molar mass and the highest content of xylan. The highest concentration of dissolved lignin was in the liquor filling the lumen cavities. The lignin in the free liquor had the lowest molar mass and the lowest content of lignin structures containing β-O-4 linkages and aliphatic hydroxyl groups. The lowest mass transfer rate of dissolved lignin was from the lumen liquor to the free liquor probably restricted by the tortuosity of the chip. 

Large amounts of cellulose-based waste textiles are generated every year, yet little is done to recycle this waste. Alternatives such as fiber-to-fiber recycling, where a significant part of the value of the waste textiles is recovered, are attractive possibilities. In this study, we have investigated the viability of using hydrated zinc chloride (ZnCl2·4H2O) as a solvent and swelling agent to convert cotton waste textiles (the most abundant cellulose-based waste textile) into a dissolving pulp that can be used as raw material for the production and spinning of viscose fibers. The solvent produced an accessible dissolving pulp and exhibited excellent recyclability, maintaining good dissolving power even after repeated recycling. The dissolving pulp was subsequently used to produce viscose dope, a spinning solution which was spun and cut into viscose staple fibers. The viscose dope exhibited good properties (moderate filter clogging value and gamma number), and the resulting staple fibers were strong and of good quality (high linear density, elongation, and tenacity). These results illustrate the potential of using hydrated zinc chloride for the production of viscose grade dissolving pulp from cotton waste textiles. 

In this study, surface-initiated ring-opening polymerization has been employed for the grafting of e-caprolactone from cellulose nanoparticles, made by partial hydrolysis of cellulose cotton linters. A sacrificial initiator was employed during the grafting reactions, to form free polymer in parallel to the grafting reaction. The degree of polymerization of the polymer grafts, and of the free polymer, was varied by varying the reaction time. The aim of this study was to estimate the cellulose nanoparticle degree of surface substitution at different reaction times. This was accomplished by combining measurement results from spectroscopy and chromatography. The prepared cellulose nanoparticles were shown to have 3.1 (±0.3) % of the total anhydroglucose unit content present at the cellulose nanoparticle surfaces. This effectively limits the amount of cellulose that can be targeted by the SI-ROP reactions. For a certain SIROP reaction time, it was assumed that the resulting degree of polymerization (DP) of the grafts and the DP of the free polymer were equal. Based on this assumption it was shown that the cellulose nanoparticle surface degree of substitution remained approximately constant (3–7 %) and seemingly independent of SI-ROP reaction time. We believe this work to be an important step towards a deeper understanding of the processes and properties controlling SI-ROP reactions occurring at cellulose surfaces.

Moisture sorption decreases dimensional stability and mechanical properties of polymer matrix biocomposites based on plant fibers. Cellulose nanofiber reinforcement may offer advantages in this respect. Here, wood-based nanofibrillated cellulose (NFC) and bacterial cellulose (BC) nanopaper structures, with different specific surface area (SSA), ranging from 0.03 to 173.3 m2/g, were topochemically acetylated and characterized by ATR-FTIR, XRD, solid-state CP/MAS 13C-NMR and moisture sorption studies. Polymer matrix nanocomposites based on NFC were also prepared as demonstrators. The surface degree of substitution (surface-DS) of the acetylated cellulose nanofibers is a key parameter, which increased with increasing SSA. Successful topochemical acetylation was confirmed and significantly reduced the moisture sorption in nanopaper structures, especially at RH = 53 %. BC nanopaper sorbed less moisture than the NFC counterpart, and mechanisms are discussed. Topochemical NFC nanopaper acetylation can be used to prepare moisture-stable nanocellulose biocomposites.

Xylan is the second most abundant polysaccharide and the most abundant hemicellulose component of soda bagasse pulp. In this study, bleached soda bagasse pulp (SB) and bleached bagasse dissolving pulp (DB) with varying amounts of xylan were fibrillated with a homogenization process. The produced fibrillated materials were used for making nanopaper structures. The surface, physical, mechanical and optical properties of the nanopaper were measured, and the effect of xylan was assessed. Laser profilometry (LP) and field emission scanning electron microscopy were applied to study the degree of the fibrillation. The pulp having the highest xylan content, SB, showed the highest yield of cellulose nanofibrils. Nanopaper produced from SB had a more consolidated structure than that produced from DB. Additionally, SB nanopaper yielded higher tensile strength, lower LP roughness, a higher barrier against oxygen and lower opacity. These results indicate a higher degree of fibrillation of the SB pulp compared to the DB pulp. Hence, the positive effect of xylan for facilitating the fibrillation of the starting pulp fibers was demonstrated.

The effect on softwood fiber wall nanostructure of kraft cooking, oxygen delignification and refining was evaluated by X-ray scattering. A recently developed simulation method for modelling small angle X-ray scattering (SAXS) data was used to estimate the apparent average sizes of solids (AAPS) and interstitial spaces in the fiber wall (AACS). Fiber saturation point and wide angle X-ray scattering were also used to calculate the pore volume in the fiber wall and the crystallite size of the fibril, respectively. The experimental modelled SAXS data was able to give consistent values for each kraft-cooked and oxygen-delignified pulp. Kraft delignification seems to have the major influence on the fiber nanostructure modification, while oxygen delignification has little or no significant impact even for different kappa numbers. The particle sizes values were more stable than the cavities sizes and no significant differences were seen between different delignification processes, refining or delignification degree. Pulps evaluated after PFI-refining, showed an increase in the fiber wall porosity evaluated by FSP and an increase in the interstitial spaces in the fiber wall, while the crystallite size and the particle sizes were very little or not affected at all. 

The fiber properties after oxygen delignification and kraft pulping were studied by looking into the chemical characteristics and morphology. The effect of the two processes on the fibers was evaluated and compared over a wider kappa number range (from 62 down to15). Wide-angle X-ray scattering, nuclear magnetic resonance and fiber saturation point were used to characterize the fiber network structure. Fiber morphology and fiber dislocations were evaluated by an optical image analysis. The total and surface fiber charges were studied by conductometric and polyelectrolyte titrations. The fiber wall supramolecular structure, such as crystallinity, size of fibril aggregates, pore size and pore volume, were similar for the two processes. The selectivity, in terms of carbohydrate yield, was equal for kraft cooking and oxygen delignification, but the selectivity in terms of viscosity loss per amount of delignification is poorer for oxygen delignification. Clearly more fiber deformations (2–6% units in curl index) in the fibers after oxygen delignification were seen. Introduction of curl depended on the physical state of the fibers, i.e. liberated or in wood matrix. In the pulping stage, the fiber continue to be supported by neighboring fibers, as the delignified chips maintain their form. However, in the subsequent oxygen stage the fibers enter in the form of pulp (liberated fibers), which makes them more susceptible to changes in fiber form. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s).

Charged groups in pulp have been shown to enhance the tensile strength of the paper produced from the pulp. Oxygen delignification introduces charged groups and it is of interest to determine how the delignification should be distributed between the cooking and the oxygen stage with respect to mechanical properties. A number of unbleached kraft cooked and oxygen delignified pulps within a wide kappa number range were produced and refined, and the effects of the refining on the morphology and mechanical properties were studied. The WRV correlated with the fiber charge and at a given fiber charge, kraft cooked and oxygen delignified pulps had the same WRV development in refining, although they had significantly different kappa numbers. The tensile strength development during refining depends on the fiber rigidity which is affected by the lignin content, the fiber charge and the chemical and mechanical processes used. Refining increased the curl of the kraft cooked pulps and decreased the curl of oxygen delignified pulps, irrespective of kappa number. A greater increase in tensile strength was seen for the pulps with a higher fiber charge and WRV, probably because of the greater degree of fibrillation achieved in the beating process. Despite the greater fiber deformation in the oxygen delignified pulps, the strength can be increased by a larger amount of charged groups and a greater swelling of the fibers. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s).

Cellulose nanofibrils, CNFs, show great potential in many application areas. One main aspect limiting the industrial use is the slow and energy demanding dewatering of CNF suspensions. Here we investigate the dewatering with a piston press process. Three different CNF grades were dewatered to solid contents between approx. 20 and 30%. The CNF grades varied in charge density (30, 106 and 604 µmol/g) and fibrillation degree. The chemical conditions were varied by changing salt concentration (NaCl) and pH and the dewatering rates were compared before and after these changes. For the original suspensions, a higher charge provides slower dewatering with the substantially slowest dewatering for the highest charged CNFs. However, by changing the conditions it dewatered as fast as the two lower charged CNFs, even though the salt/acid additions also improved the dewatering rate for these two CNFs. Finally, by tuning the conditions, fast dewatering could be obtained with only minor effect on film properties (strength and oxygen barrier) produced from redispersed dispersion. However, dewatering gives some reduction in viscosity of the redispersed dispersions. This may be a disadvantage if the CNF application is as e.g. rheology modifier or emulsion stabilizer. Graphical abstract: [Figure not available: see fulltext.].

Carboxylated cellulose nanofibers (CNFs), having an average width of 7 nm and thickness of 1.5 nm, were produced by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation method. The fiber cross-sectional dimensions were determined using small-angle X-ray scattering (SAXS), transmission electron microscopy and atomic force microscopy techniques, where the rheological properties under different concentration and ionic strength were also investigated. The formation of hydrogel was evidenced by increasing the CNF concentration or ionic strength of the solvent (water), while the gel structure in ion-induced CNF hydrogels was found to be relatively inhomogeneous. The gelation behavior was closely related to the segmental aggregation of charged CNF, which could be quantitatively characterized by the correlation length (Ο) from the low-angle scattering profile and the scattering invariant (Q) in SAXS.

In the present work the evolution of physical and mechanical properties of papers and nanopapers is studied. Handsheets made of eucalyptus fibres reinforced with 0, 25, 50, 75 and 100 wt% of nanofibrillated cellulose (NFC) content were fabricated using a Rapid Köthen-like equipment. The obtained papers and nanopapers were physical- and mechanically-characterized. The results showed a significant increase in density and a reduction of porosity in the samples during their transition from paper to nanopaper; besides, nanopapers were more transparent and smoother than normal papers. These physical changes where more evident with increasing amounts of NFC. Regarding mechanical properties, nanopapers with a 100 wt% content of NFC improved their strength and rigidity in 228 and 317 %, respectively, in comparison with normal papers. The evolution of strength and rigidity from paper to nanopaper was linear in relation to the amount of NFC, which means that the ultimate tensile strength was mainly dependant on nanofibril failure.

Parenchyma cells and fibers are the two dominant types of cells in the bamboo culm. Their mechanical and biological functions in bamboo differ substantially, derived from their cell wall structures and chemical compositions. The objective of this work was to comparatively study the hygroscopicity and the thermal degradation of bamboo fibers and parenchyma cells in order to better understand how to optimize heat treatment of bamboo. FTIR spectroscopy showed that parenchyma cells had a higher hemicellulose content and higher S/G lignin ratio than bamboo fibers based on the spectral changes at 1602 cm−1 with respect to 1505 cm−1. Upon heat treatment, spectral changes related to esterification reactions and loss of hydroxyl groups were observed. The heat treatment reduced hygroscopicity of parenchyma cells more than for bamboo fibers due to their lower thermal stability attributed to the higher hemicellulose content and less compact cell wall structure. Although heat treatment at 180 °C could improve the thermal stability of bamboo, mild heat treatments at 140 °C and 160 °C were found to be adequate to facilitate the degradation of bamboo. © 2021, The Author(s)

In this study the effect of the mercerization degree on the water retention value (WRV) and tensile properties of compression molded sulphite dissolving pulp was evaluated. The pulp was treated with 9, 10, or 11 % aqueous NaOH solution for 1 h before compression molding. To study the time dependence of mercerization the pulp was treated with 12 wt% aqueous NaOH for 1, 6 or 48 h. The cellulose I and II contents of the biocomposites were determined by solid state cross polarization/magic angle spinning carbon 13 nuclear magnetic resonance (CP/MAS 13C NMR) spectroscopy. By spectral fitting of the C6 and C1 region the cellulose I and II content, respectively, could be determined. Mercerization decreased the total crystallinity (sum of cellulose I and cellulose II content) and it was not possible to convert all cellulose I to cellulose II in the NaOH range investigated. Neither increased the conversion significantly with 12 wt% NaOH at longer treatment times. The slowdown of the cellulose I conversion was suggested as being the result from the formation of cellulose II as a consequence of coalescence of anti-parallel surfaces of neighboring fibrils (Blackwell et al. in Tappi 61:71-72, 1978; Revol and Goring in J Appl Polym Sci 26:1275-1282, 1981; Okano and Sarko in J Appl Polym Sci 30:325-332, 1985). Compression molding of the partially mercerized dissolving pulps yielded biocomposites with tensile properties that could be correlated to the decrease in cellulose I content in the pulps. Mercerization introduces cellulose II and disordered cellulose and lowered the total crystallinity reflected as higher water sensitivity (higher WRV values) and poorer stiffness of the mercerized biocomposites.

Abstract: Coagulation of cellulose solutions is a process whereby many useful materials with variable microstructures and properties can be produced. This study investigates the complexity of the phase separation that generates the structural heterogeneity of such materials. The ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), and a co-solvent, dimethylsulfoxide (DMSO), are used to dissolve microcrystalline cellulose in concentrations from 5 to 25 wt%. The solutions are coagulated in water or 2-propanol (2PrOH). The coagulated material is then washed and solvent exchanged (water → 2PrOH → butanone → cyclohexane) in order to preserve the generated microstructures upon subsequent drying before analysis. Sweep electron microscopy images of 50 k magnification reveal open-pore fibrillar structures. The crystalline constituents of those fibrils are estimated using wide-angle X-ray spectroscopy and specific surface area data. It is found that the crystalline order or crystallite size is reduced by an increase in cellulose concentration, by the use of the co-solvent DMSO, or by the use of 2PrOH instead of water as the coagulant. Because previous theories cannot explain these trends, an alternative explanation is presented here focused on solid–liquid versus liquid–liquid phase separations. Graphical abstract: [Figure not available: see fulltext.].

Abstract: Cellulose can be regenerated from cellulose-ionic liquid (IL) solutions by immersion in water or alcohols. These compounds are potent non-solvents due to their proton-donating ability in hydrogen bonds to IL anions. Although they share this fundamental way of reducing IL solvent quality, coagulation in water is distinctly different from coagulation in alcohols with regard to the microstructures formed and the mechanisms that generate the microstructures. In this study, the possibility of mass-transport effects on microstructures was investigated. The mass-transport of all components: non-solvent (EtOH, 2PrOH), IL ([C2mim][OAc]), and a co-solvent (DMSO), during coagulation was studied. The data was compared to previous data with water as the non-solvent. Results showed that diffusion is essentially limited to a continuous non-solvent-rich phase that is formed during phase separation in all non-solvents. There were also significant differences between non-solvents. For instance, [C2mim][OAc] diffusion coefficients were 6–9 times smaller in 2PrOH than in water, and there were apparent effects from cellulose concentration in 2PrOH that were not observed in water. The differences stem from the interactions between solvent, non-solvents, and cellulose, which can be both mutual and competitive. Weaker [C2mim][OAc]-non-solvent interactions with alcohols give more persistent [C2mim][OAc]-cellulose interactions than with water as the non-solvent, which has consequences for mass-transport. Graphic abstract: [Figure not available: see fulltext.].

Inks for 3D printing based on cellulose nanofibrils (CNFs) or mixtures of CNFs and either cellulose nanocrystals (CNCs) or alginate were assessed by determining their viscoelastic properties i.e. complex viscosity and storage and loss moduli (G′ and G″). Two types of alginates were used, i.e. from Laminaria hyperborea stipe and Macrocystis pyrifera. Shape fidelity of 3D printed grids were qualitatively evaluated and compared to the viscoelastic properties of the inks. The biocomposite gels containing alginate were post stabilized by crosslinking with Ca2+. Mechanical properties of the crosslinked biocomposite gels were assessed. The complex viscosity, G′ and G″ of CNF suspensions increased when the solid content was increased from 3.5 to 4.0 wt%, but levelled off by further increase in CNF solid content. The complex viscosity at low angular frequency at 4 wt% was as high as 104 Pa·s. This seemed to be the necessary viscosity level for obtaining good shape fidelity of the printed structures for the studied systems. By replacing part of the CNFs with CNCs, the complex viscosity, G′ and G″ were reduced and so was also the shape fidelity of the printed grids. The changes in complex viscosity and moduli when CNFs was replaced with alginate depended on the relative amounts of CNFs/alginate. The type of alginate (from either L. hyp. stipe or M. pyr.) did not play a role for the viscoelastic properties of the inks, nor for the printed grids before post stabilization. Replacing CNFs with up to 1.5 wt% alginate gave satisfactory shape fidelity. The effect of adding alginate and subsequent crosslinking with Ca2+, strongly affected the strength properties of the gels. By appropriate choice of relative amounts of CNFs and alginate and type of alginate, the Young’s modulus and rupture strength could be controlled within the range of 30–150 kPa and 1.5–6 kg, respectively. The deformation at rupture was around 55%. The alginate from L. hyp. stipe yields higher Young’s modulus and lower syneresis compared to M. pyr. This shows that the choice of alginate plays a significant role for the mechanical properties of the final product, although it does not influence on the viscoelastic properties of the ink. The choice of alginate should be L. hyp. stipe if high strength is desired.

Abstract: It is predicted that the forest and materials from the forest will play an important role to enable the transformation from our linear present to a circular and sustainable future. Therefore, there is a need to understand the materials that can be extracted from the forest, and how to use them in an efficient manner. Here, carboxymethylated cellulose nanofibrils (CNF) from the forest are used to produce films and filaments with the aim to preserve the impressive mechanical properties of a single CNF in a macro-scale material. The mechanical properties of both the films (tensile strength of 231 MPa) and filaments (tensile strength of 645 MPa) are demonstrated to be maximized when the starting suspension is in a flowing state. This is a new insight with regards to filament spinning of CNF, and it is here argued that the three main factors contributing to the mechanical properties of the filaments are (1) the possibility to produce a self-supporting filament from a suspension, (2) the CNF alignment inside the filament and (3) the spatial homogeneity of the starting suspension. The results in this study could possibly also apply to other nanomaterials such as carbon nanotubes and silk protein fibrils, which are predicted to play a large part in future high performing applications. 

We have found that the dissolution of cellulose in the binary mixed solvent tetrabutylammonium acetate/dimethyl sulfoxide follows a previously overlooked near-stoichiometric relationship such that one dissolved acetate ion is able to dissolve an amount of cellulose corresponding to about one glucose residue. The structure and dynamics of the resulting cellulose solutions were investigated using small-angle X-ray scattering (SAXS) and nuclear magnetic resonance techniques as well as molecular dynamics simulation. This yielded a detailed picture of the dissolution mechanism in which acetate ions form hydrogen bonds to cellulose and causes a diffuse solvation sheath of bulky tetrabutylammonium counterions to form. In turn, this leads to a steric repulsion that helps to keep the cellulose chains apart. Structural similarities to previously investigated cellulose solutions in aqueous tetrabutylammonium hydroxide were revealed by SAXS measurement. To what extent this corresponds to similarities in dissolution mechanism is discussed.

A techno-economic assessment of an upgrading procedure and outtake of a pre-hydrolysate in a presumed dissolving pulp mill was performed. Pre-hydrolysis of spruce wood chips in pilot scale produced input data for energy and mass balances and was performed with and without subsequent membrane filtration to produce hydrolysate fractions rich in galactoglucomannan and with some lignin. The hydrolysate is a viable raw material for the production of renewable thin oxygen barrier films as demonstrated herein in the formulation of free standing films with very low oxygen permeability at both moderate and high relative humidities. Approximately 50,000 ton dry solid upgraded pre-hydrolysate suitable for production of oxygen barriers could be produced according to the presumed dissolving pulp mill producing about 500,000 air dry ton dissolving pulp per year and applying a liquor to wood ratio of 4:1. Utilization of the pre-hydrolysis liquor hence adds value to and realizes the dissolving plant as a biorefinery. A sensitivity analysis indicates that the market price of the upgraded pre-hydrolysate has the largest positive effect on the return on investment for separation and upgrading of a pre-hydrolysate. Increased investment cost and increased annuity factor show negative effects.

Total and surface charge of three different carboxymethylated nanofibrillated/microfibrillated cellulose (NFC/MFC) samples were investigated by using titrimetric methods (conductometric and polyelectrolyte (PE) titrations). Conductometric titration was found to be suitable method for the NFC total charge measurements when the back titration with HCl was applied. Surface charge measurements of NFC/MFC were conducted by using both indirect and direct PE titrations. The direct PE titration was found to be a more suitable method for the surface charge determination of NFC/MFC whereas the indirect PE titration produced too high surface charge values. This is presumably due to kinetically locked polyelectrolyte conformations on the NFC/MFC surfaces or entrapment of residual polymer after adsorption onto the NFC/MFC gel network. Finally, NFC was propargyl-functionalized and the changes in surface and total charge were successfully monitored and compared to those of propargyl-functionalized pulp. A good correlation between the titrimetric methods and elemental analysis was observed. 

Herein, we present a route to obtain bi-functional cellulose nanofibrils (CNF) by a one-pot approach using an already established functionalisation route, carboxymethylation, to which a subsequent functionalisation step, allylation or alkynation, has been added in the same reaction pot, eliminating the need of solvent exchange procedures. The total charge of the fibres and the total surface charge of the nanofibrils were determined by conductometric and polyelectrolyte titration, respectively. Furthermore, the allyl and alkyne functionalised cellulose were reacted with methyl 3-mercaptopropionate and azide-functionalised disperse red, respectively, to estimate the degree of functionalisation. The samples were further assessed by XPS and FT-IR. Physical characteristics were evaluated by CP/MAS 13C-NMR, XRD, AFM and DLS. This new approach of obtaining bi-functionalised CNF allows for a facile and rapid functionalisation of CNF where chemical handles can easily be attached and used for further modification of the fibrils. Graphical abstract: [Figure not available: see fulltext.

Foamed materials are gaining an increased interest due to their good mechanical properties in relation to their low densities and an increased industrial demand can be expected. A few less attractive issues can however be associated with commodity foamed products. For instance the raw-material often originates from non-renewable, fossil-based, sources. Furthermore, degradation in nature is slow, therefor the disposed product is burned or end up in landfills. One possibility to reduce the impact on nature could be to produce foams from natural polymers such as starch or cellulose. In this study the possibility to produce foams from hydroxypropyl methylcellulose (HPMC) with water as blowing agent, by continuous extrusion, was investigated. A pre-study using a capillary viscometer, batch-extruder, was conducted to evaluate the foamability of HPMC. Due to promising results further experiments were conducted with a single-screw extruder. The goal was to find an adequate processing window for foaming. It was concluded that HPMC could successfully be foamed by continuous extrusion, although a careful tailoring of the processing parameters was required. Crucial parameters were here the temperature, pressure and residence time distribution in the extruder. Regions of the extruded foams were examined using optical and scanning electron microscopy and HPMC foams with a density in the range of that of fossil-based polymeric foams could be produced.

Hydroxypropyl methylcellulose and ethyl hydroxyethyl cellulose could be interesting candidates for production of lightweight, foamed packaging material originating from non-fossil, renewable resources. The foaming ability of nine different grades of the two cellulose derivatives, using water as the blowing agent, was investigated using a hot-mold process. The foaming process was studied by evaluating the water loss during the heating, both in a real-time experiment and by thermal gravimetric analysis. Further, the development of the rheological properties of the derivative-water mixtures during a simulated foaming process was assessed using dynamical mechanical thermal analysis and viscosity measurements. Five of the studied derivatives showed promising properties for hot-mold foaming and the final foams were characterized with regard to their apparent density. It was concluded that the foamability of these systems seems to require a rather careful tailoring of the viscoelastic properties in relation to the water content in order to ensure that a network structure is built up and expanded during the water evaporation.

Abstract: In present study, cellulose nanowhiskers (CNWs) were isolated from roselle fibers by employing low-medium amplitudes of ultrasonication. In a range of low-to-moderate amplitudes of ultrasound, 20%, 30% and 40% amplitudes were applied during ultrasonication treatment to produce CNW-I, CNW-II and CNW-III particles, respectively. The morphological (TEM, FESEM, and AFM), physicochemical (FTIR, EDS, DLS, and XRD) and thermal properties (TGA and DSC) of produced CNWs were conducted to understand the effect of applied amplitudes on CNWs properties. It is clear from the FTIR spectra that increasing ultrasonic amplitudes enhanced crystalline of CNWs. In TEM analysis, CNWs sonicated with 30% and 40% amplitudes possessed the shape of elongated rod-like nanoparticles. FESEM and AFM micrographs exhibited varying whisker-like nanostructures. Additionally, both CNW-II and CNW-III showed stable aqueous colloidal suspensions with zeta potential values more than − 25 mV in response to high sulfur content. As for XRD evaluation, CNW-III exhibited the higher crystallinity degree of 79.9% amongst the all samples. Based on thermal analysis, CNW-I and CNW-II possessed high heat resistant capability at elevated temperature. These CNWs are potential reinforcements in nanocomposites for diverse applications in packaging, engineering, composites and biomedical fields.

There is an increased interest in the use of cellulose nanocrystal (CNC) films and coatings for a range of functional applications in the fields of material science, biomedical engineering, and pharmaceutical sciences. Most of these applications have been demonstrated on films and coatings produced using laboratory-scale batch processes, such as solvent casting, dip coating, or spin coating. For successful coating application of CNC suspensions using a high throughput process, several challenges need to be addressed: relatively high viscosity at low solids content, coating brittleness, and potentially poor adhesion to the substrate. This work aims to address these problems. The impact of plasticizer on suspension rheology, coating adhesion, and barrier properties was quantified, and the effect of different pre-coatings on the wettability and adhesion of CNC coatings to paperboard substrates was explored. CNC suspensions were coated onto pre-coated paperboard in a roll-to-roll process using a custom-built slot die. The addition of sorbitol reduced the brittleness of the CNC coatings, and a thin cationic starch pre-coating improved their adhesion to the paperboard. The final coat weight, dry coating thickness, and coating line speed were varied between 1–11 g/m2, 900 nm–7 µm, and 2.5–10 m/min, respectively. The barrier properties, adhesive strength, coating coverage, and smoothness of the CNC coatings were characterized. SEM images show full coating coverage at coat weights as low as 1.5 g/m2. With sorbitol as plasticizer and at coat weights above 3.5 g/m2, heptane vapor and water vapor transmission rates were reduced by as much as 99% and 75% respectively. Compared to other film casting techniques, the process employed in this work deposits a relatively thick coating in significantly less time, and may therefore pave the way toward various functional applications based on CNCs.

In this work a multilayer barrier paperboard was produced in a roll-to-roll process by slot-die coating of nanocellulose (microfibrillated cellulose or carboxymethylated cellulose nanofibrils) followed by extrusion coating of biodegradable thermoplastics (polylactic acid, polybutylene adipate terephthalate and polybutylene succinate). Hyperplaty kaolin pigments were blended in different ratios into nanocellulose to tailor the barrier properties of the multilayer structure and to study their influence on adhesion to the thermoplastic top layer. Influence of a plasticizer (glycerol) on flexibility and barrier performance of the multilayer structure was also examined. Water vapor permeance for the multilayer paperboard was below that of control single-layer thermoplastic materials, and oxygen permeance of the coated structure was similar or lower than that of pure nanocellulose films. Glycerol as a plasticizer further lowered the oxygen permeance and kaolin addition improved the adhesion at the nanocellulose/thermoplastic interface. The results provide insight into the role played by nanocelluloses, thermoplastics, pigments, and plasticizers on the barrier properties when these elements are processed together into multilayer structures, and paves the way for industrial production of sustainable packaging. 

Wood-derived TEMPO-oxidized cellulose nanofibrils (CNFs) have potential as scaffolding for bone tissue engineering. Although biocompatible, the material lacks osteoconductive and appropriate mechanical properties. Incorporation of nano-hydroxyapatite (nHA) and modification of scaffold preparation methods could improve applicability. In this study, freeze-dried porous scaffolds were prepared using a range of nHA (0, 20, 33, 50%) and CNF compositions. Not only the microarchitecture but also the chemical composition of the scaffolds was studied. Osteoblast-like osteosarcoma derived cells (Saos-2) were cultured on the scaffolds and their responses (viability, attachment, proliferation, and osteogenic phenotype) to the different scaffolds were documented. The results show that incorporation of nHA influenced the microarchitecture, mechanical stiffness and surface properties of the scaffolds. Moreover, biological characterization demonstrated good cell viability in all the groups. However, the increase of nHA concentration beyond 20% does not offer further advantages. It is concluded that the incorporation of 20% nHA resulted in the widest and most biomimetic pore size distribution, increased surface roughness and improved protein adsorption. These changes in material properties enhanced cell spreading and the osteogenic gene expression of osteoblast-like cells seeded on the scaffolds. Moreover, 20% nHA warrants further investigation as a potential scaffolding material for bone tissue engineering. Graphical abstract: (Figure presented.).

Wood and wood materials are highly sensitive to moisture in the environment. To a large extent this relates to the hygroscopicity of wood hemicelluloses. In order to increase our understanding of the effects of moisture sorption of the major wood hemicelluloses, glucomannan and xylan, model experiments using films of amorphous konjak glucomannan and rye arabinoxylan were conducted. Moisture-induced expansion and stiffness softening were characterized using dynamic mechanical testing. Both hemicelluloses showed a threshold around 5 % of moisture content above which swelling increased whereas the modulus decreased by more than 70 %. FTIR spectra, using H2O and D2O, indicated that even at high RH about 15 % of the hydroxyl groups were not accessible to hydrogen exchange by D2O. For xylan both hydroxyl groups were found to exchange in the same manner while for the glucomannan the O(6)H group seemed to be the most accessible.

The effect of digestion conditions (amount of effective alkali, digestion time) on the surface compositions of unbleached softwood (Pinus sylvestris) kraft pulp has been investigated by ESCA analysis. The quantities monitored were the angular dependence of the total O/C ratio, the relative amounts of carbons in different states of oxidation and the adsorption of Al and Ca ions to the carboxyl groups in the surface. Analysis of the angular dependence of ESCA intensities shows that the concentration of alkyl carbon is high in a very thin surface layer. This enrichment becomes more marked as the lignin content (kappa number) decreases, but it is not affected by extraction of the fibres with dichloromethane. It is concluded that the observed distribution is due to re-precipitation of lignin. In pulp that has not been extracted, there is also strong enrichment of extractives in the surface. This amount increases with increasing effective alkali but is relatively independent of the time of digestion. ESCA analysis of the Al and Ca bound to the carboxyl groups shows that the amount of these depends on digestion time; the results are consistent with the notion that the reprecipitated lignin contains carboxyl groups.

Hygroexpansion, CP/MAS 13C-NMR, WAXS and SAXS measurements were carried out on sheets made from four different commercial pulps of varying lignin content. Non-directional laboratory sheets were made at different press levels from the pulps following different degrees of beating. The sheets were dried both freely and with restraints. Measurements were made on sheets before and after moisture cycling to determine hygroexpansion coefficients, changes in cellulose average lateral fibril dimensions and average cellulose crystallite sizes, with the aim of understanding macroscale and nanoscale changes as the result of moisture cycling. Within the sheets consistent and statistically significant structural changes were observed on both macro and nanoscale. On the macroscale, moisture cycling consistently induced irreversible shrinkage in sheets dried with restraints, but less so in the case of sheets dried freely. The hygroexpansion coefficients were typically higher for freely dried sheets compared with sheets dried with constraints. On the nanoscale, moisture cycling consistently caused an increase in the average crystallite sizes (WAXS) and the average lateral fibril dimensions (CP/MAS 13C-NMR), though the latter occurred with poor statistical significance. These changes were interpreted as an increase in the degree of order in the cellulose fibril interior/cellulose crystallite. There were no profound differences in the nanoscale changes observed for sheets dried with restraints and for sheets dried freely. Changes in the fibre wall nanostructure were of similar magnitudes when comparing results from freely dried low grammage sheets (less abundant inter-fibre joints) with freely dried sheets of higher grammage (more abundant inter-fibre joints). No obvious correlations were found between the macroscale and nanoscale measurements. The proposed explanation for this was that the nanoscale structural changes occurred similarly throughout the entirety of the fibre wall, independent of the proximity to an inter-fibre joint, and that the nanoscale structural changes were mainly the result of water penetrating into the interior of cellulose fibril aggregates. By using the same fibril model for evaluation of CP/MAS 13C-NMR and WAXS data, good-to-reasonable agreement were found for estimates of the degree of cellulose crystallinity. 

A simulation method was developed for modelling SAXS data recorded on cellulose rich pulps. The modelling method is independent of the establishment of separate form factors and structure factors and was used to model SAXS data recorded on dense samples. An advantage of the modelling method is that it made it possible to connect experimental SAXS data to apparent average sizes of particles and cavities at different sample solid contents. Experimental SAXS data could be modelled as a superposition of a limited number of simulated intensity components and gave results in qualitative agreement with CP/MAS 13C-NMR data recorded on the same samples. For the water swollen samples, results obtained by the SAXS modelling method and results obtained from CP/MAS 13C-NMR measurements, agreed on the ranking of particle sizes in the different samples. The SAXS modelling method is dependent on simulations of autocorrelation functions and the time needed for simulations could be reduced by rescaling of simulated correlation functions due to their independence of the choice of step size in real space. In this way an autocorrelation function simulated for a specific sample could be used to generate SAXS intensity profiles corresponding to all length scales for that sample and used for efficient modelling of the experimental data recorded on that sample. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s).

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.

A problem with cellulose-based materials is that they are highly influenced by moisture, leading to reduced strength properties with increasing moisture content. By achieving a more detailed understanding of the water–cellulose interactions, the usage of cellulose-based materials could be better optimized. Two different exchange processes of cellulose hydroxyl/deuteroxyl groups have been monitored by transmission FT-IR spectroscopy. By using line-shape-assisted deconvolution of the changing intensities, we have been able to follow the exchange kinetics in a very detailed and controlled manner. The findings reveal a hydrogen exchange that mainly is located at two different kinds of fibril surfaces, where the differences arise from the water accessibility of that specific surface. The slowly accessible regions are proposed to be located between the fibrils inside of the aggregates, and the readily accessible regions are suggested to be at the surfaces of the fibril aggregates. It was also possible to identify the ratio of slowly and readily accessible surfaces, which indicated that the average aggregate of cotton cellulose is built up by approximately three fibrils with an assumed average size of 12 × 12 cellulose chains. Additionally, the experimental setup enabled visualizing and discussing the implications of some of the deviating spectral features that are pronounced when recording FT-IR spectra of deuterium-exchanging cellulose: the insufficient red shift of the stretching vibrations and the vastly decreasing line widths.