On the role of hydrophobic interactions in cellulose dissolution and regeneration: Colloidal aggregates and molecular solutions

Impact of coagulation solvent interactions on porous morphology evolution in cellulose xerogels

The role of coagulation solvent interactions on the pore formation mechanism in cellulose xerogels was investigated using single-step coagulation baths. A series of cellulose xerogels were fabricated from cotton yarns partially dissolved in ionic liquid (i.e., 1-ethyl-3-methylimidazolium acetate) and then immersed in one of seven different coagulation baths. These samples were evaluated using N2 physisorption, inverse gas chromatography, and X-ray photoelectron spectroscopy. The regenerated cellulose orientation and resultant surface hydrophilicity was found to be dependent on solvent solubility interactions with an emphasis on polar interaction and dispersion force strength. More importantly, the xerogel specific surface area dramatically decreased from 100 m2g-1 to 0.278 m2g-1 with increasing hydrophilicity, confirming the importance of controlled cellulose orientation during the coagulation step of cellulose xerogel fabrication. These results have been used to propose a new pore formation mechanism in cellulose xerogels and provide recommendations towards the development of controllable porosity during xerogel fabrication.

β-Cyclodextrin Modified Hydrogels of Kappa-Carrageenan for Methotrexate Delivery

This work is aimed at developing a kappa-carrageenan (kCR) gel with increased methotrexate (MTX) content. β-Cyclodextrin (βCD), which is able to inclusion complex formation with MTX, has been used to increase the drug concentration in the hydrogel. The rheological behavior of the designed gels was investigated and the influence of MTX and βCD on the viscoelastic properties of kCR gel was studied in detail. The effect of βCD and its concentration on the MTX-releasing rate from the kCR gels was examined. The properties of kappa- and iota-carrageenans loaded with MTX were compared and the differences observed were explained in terms of different binding affinities of MTX to these polymers. The obtained gels provided desirable viscoelastic properties useful for topical application.

Perspectives on the Lindman Hypothesis and Cellulose Interactions

In the history of cellulose chemistry, hydrogen bonding has been the predominant explanation when discussing intermolecular interactions between cellulose polymers. This is the general consensus in scholarly textbooks and in many research articles, and it applies to several other biomacromolecules' interactions as well. This rather unbalanced description of cellulose has likely impacted the development of materials based on the processing of cellulose-for example, via dissolution in various solvent systems and regeneration into solid materials, such as films and fibers, and even traditional wood fiber handling and papermaking. In this review, we take as a starting point the questioning of the general description of the nature of cellulose and cellulose interactions initiated by Professor Björn Lindman, based on generic physicochemical reasoning about surfactants and polymers. This dispute, which became known as "the Lindman hypothesis", highlights the importance of hydrophobic interactions in cellulose systems and that cellulose is an amphiphilic polymer. This paper elaborates on Björn Lindman's contribution to the subject, which has caused the scientific community to revisit cellulose and reconsider certain phenomena from other perspectives.

Probing cellulose-solvent interactions with self-diffusion NMR: Onium hydroxide concentration and co-solvent effects

The molecular self-diffusion coefficients were accessed, for the first time, in solutions of microcrystalline cellulose, dissolved in 30 wt% and 55 wt% aqueous tetrabutylammonium hydroxide, TBAH (aq), and in mixtures of 40 wt% TBAH (aq) with an organic co-solvent, dimethylsulfoxide (DMSO), through pulsed field gradient stimulated echo NMR measurements. A two-state model was applied to estimate α (i.e., average number of ions that "bind" to each anhydroglucose unit) and P_b (i.e., fraction of "bound" molecules of DMSO, TBAH or H₂O to cellulose) parameters. The α values suggest that TBA⁺ ions can bind to cellulose within 0.5 TBA⁺ to 2.3 TBA⁺/AGU. On the other hand, the P_b parameter increases when raising cellulose concentration for TBA⁺, DMSO and water in all solvent systems. Data suggests that TBAH interacts with the ionized OH groups from cellulose forming a sheath of bulky TBA⁺ counterions which consequently leads to steric hindrance between cellulose chains.

Dissolution of cellulose into supercritical water and its dissolving state followed by structure formation from the solution system

Cellulose was treated with supercritical water at 668 K and 25 MPa for 0.04 s in this study. The cellulose/water system was transparent at room temperature for a while after supercritical water treatment before a precipitate gradually appeared over several hours. The precipitation process was monitored by synchrotron X-ray scattering. The scattering functions of fractal systems and flat-like structures were utilized to explain the experimentally observed small-angle scattering profiles. Immediately after supercritical water treatment, the cellulose appeared to dissolve with a fractal dimension D of approximately 1, indicating that the cellulose molecules were rigid, followed by aggregation into a 5-nm-thick flat-like structure. The flat-like structure was determined to be similar to the molecular sheets observed during the early stages of precipitation in the cellulose/aqueous sodium hydroxide and cellulose/aqueous lithium hydroxide/urea systems. Resultant regenerated cellulose had high crystallinity, large crystal size, and a low degree of polymerization.

Lignin enhances cellulose dissolution in cold alkali

Aqueous sodium hydroxide solutions are extensively used as solvents for lignin in kraft pulping. These are also appealing systems for cellulose dissolution due to their inexpensiveness, ease to recycle and low toxicity. Cellulose dissolution occurs in a narrow concentration region and at low temperatures. Dissolution is often incomplete but additives, such as zinc oxide or urea, have been found to significantly improve cellulose dissolution. In this work, lignin was explored as a possible beneficial additive for cellulose dissolution. Lignin was found to improve cellulose dissolution in cold alkali, extending the NaOH concentration range to lower values. The regenerated cellulose material from the NaOH-lignin solvents was found to have a lower crystallinity and crystallite size than the samples prepared in the neat NaOH and NaOH-urea solvents. Beneficial lignin-cellulose interactions in solution state appear to be preserved under coagulation and regeneration, reducing the tendency of crystallization of cellulose.

Characterization of hydrophobic interaction of galactomannan in aqueous solutions using fluorescence-based technique

Fluorescence probing was used to study hydrophobic interactions of galactomannan (GM) obtained from fenugreek gum (FG), guar gum (GG), and locust bean gum (LBG) at different M/G ratios. The I₁/I₃ ratio of pyrene changed from 1.73 to 1.29, 1.22, and 1.29 for FG, GG and LBG, respectively, as the concentration of GM increased from 0.01 to 8.0 g/L at 30 °C. The critical aggregation concentration of FG, GG, and LBG increased from 1.04 to 3.84 g/L, 1.15 to 3.73 g/L, and 0.94 to 3.63 g/L, respectively, as temperature increased from 10 to 70 °C. Addition of Na₂SO₄ and NaSCN increased the I₁/I₃ ratio in dilute solution, but reduced it in semi-dilute solution, whereas adding urea reduced I₁/I₃ in dilute solution but increased it in semi-dilute solution. These results indicated that the CAC of GM, polarity and number of hydrophobic microdomains were highly dependent on the M/G ratio and galactose distribution.

Self-assembly of cellulose for creating green materials with tailor-made nanostructures

Inspired by living systems, biomolecules have been employed in vitro as building blocks for creating advanced nanostructured materials. In regard to nucleic acids, peptides, and lipids, their self-assembly pathways and resulting assembled structures are mostly encoded in their molecular structures. On the other hand, outside of its chain length, cellulose, a polysaccharide, lacks structural diversity; therefore, it is challenging to direct this homopolymer to controllably assemble into ordered nanostructures. Nevertheless, the properties of cellulose assemblies are outstanding in terms of their robustness and inertness, and these assemblies are attractive for constructing versatile materials. In this review article, we summarize recent research progress on the self-assembly of cellulose and the applications of assembled cellulose materials, especially for biomedical use. Given that cellulose is the most abundant biopolymer on Earth, gaining control over cellulose assembly represents a promising route for producing green materials with tailor-made nanostructures.

Plant Nanomaterials and Inspiration from Nature: Water Interactions and Hierarchically Structured Hydrogels

Recent developments in the area of plant-based hydrogels are introduced, especially those derived from wood as a widely available, multiscale, and hierarchical source of nanomaterials, as well as other cell wall elements. With water being fundamental in a hydrogel, water interactions, hydration, and swelling, all critically important in designing, processing, and achieving the desired properties of sustainable and functional hydrogels, are highlighted. A plant, by itself, is a form of a hydrogel, at least at given states of development, and for this reason phenomena such as fluid transport, diffusion, capillarity, and ionic effects are examined. These aspects are highly relevant not only to plants, especially lignified tissues, but also to the porous structures produced after removal of water (foams, sponges, cryogels, xerogels, and aerogels). Thus, a useful source of critical and comprehensive information is provided regarding the synthesis of hydrogels from plant materials (and especially wood nanostructures), and about the role of water, not only for processing but for developing hydrogel properties and uses.

Hydrophobic interactions control the self-assembly of DNA and cellulose

Desoxyribosenucleic acid, DNA, and cellulose molecules self-assemble in aqueous systems. This aggregation is the basis of the important functions of these biological macromolecules. Both DNA and cellulose have significant polar and nonpolar parts and there is a delicate balance between hydrophilic and hydrophobic interactions. The hydrophilic interactions related to net charges have been thoroughly studied and are well understood. On the other hand, the detailed roles of hydrogen bonding and hydrophobic interactions have remained controversial. It is found that the contributions of hydrophobic interactions in driving important processes, like the double-helix formation of DNA and the aqueous dissolution of cellulose, are dominating whereas the net contribution from hydrogen bonding is small. In reviewing the roles of different interactions for DNA and cellulose it is useful to compare with the self-assembly features of surfactants, the simplest case of amphiphilic molecules. Pertinent information on the amphiphilic character of cellulose and DNA can be obtained from the association with surfactants, as well as on modifying the hydrophobic interactions by additives.

Fibre-based oleogels: effect of the structure of insoluble fibre on its physical properties

Solid fat is a "staple" in the modern diet in the form of products such as butter, margarine, and shortening. Due to its potentially detrimental effects on health, numerous dietary guidelines recommend its restriction. This opens up opportunities to develop fat replacers via edible oil structuring. In this study, we report the development of a unique, non-thermal method to create oleogels which contain only natural food fibres and liquid vegetable oil. Moreover, they do not oil off on compression. The objective was to understand how the structure of insoluble fibre influenced the physical properties of oleogels, specifically physical robustness and apparent melting point. The fibres studied were citrus fibre of different particle sizes, and nata de coco fibre known for its thinner dimension and finer three-dimensional structure. The melting characteristics of oleogels were studied by differential scanning calorimetry and visual observation. The physical robustness of oleogels was characterised by the spreadability method using a texture analyser. The presence of fibre was found to disrupt fat crystallisation, leading to proportionately more crystal species that were less stable. However, the true melting point of fat was not significantly altered. Despite greater disruption, oleogels made with longer and/or more extensive fibres were mainly firmer and capable of keeping the oil in the solid oleogel form, even under elevated temperatures. Our novel approach for manufacturing oleogels opens up a range of opportunities for their application in various products and systems.

Revisiting the dissolution of cellulose in H3PO4(aq) through cryo-TEM, PTssNMR and DWS

Cellulose can be dissolved in concentrated acidic aqueous solvents forming extremely viscous solutions, and, in some cases, liquid crystalline phases. In this work, the concentrated phosphoric acid aqueous solvent is revisited implementing a set of advanced techniques, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR), and diffusing wave spectroscopy (DWS). Cryo-TEM images confirm that this solvent system is capable to efficiently dissolve cellulose. No cellulose particles, fibrils, or aggregates are visible. Conversely, PTssNMR revealed a dominant CP signal at 25 °C, characteristic of C-H bond reorientation with correlation time longer than 100 ns and/or order parameter above 0.5, which was ascribed to a transient gel-like network or an anisotropic liquid crystalline phase. Increasing the temperature leads to a gradual transition from CP to INEPT-dominant signal and a loss of birefringence in optical microscopy, suggesting an anisotropic-to-isotropic phase transition. Finally, an excellent agreement between optical microrheology and conventional mechanical rheometry was also obtained.

Effect of Cellulose Solvents on the Characteristics of Cellulose/Fe2O3 Hydrogel Microspheres as Enzyme Supports

Cellulose hydrogels are considered useful biocompatible and biodegradable materials. However, as few cellulose-dissolving solvents can be used to prepare cellulose hydrogel microspheres, the use of unmodified cellulose-based hydrogel microspheres for enzyme immobilization remains limited. Here, we prepared cellulose/Fe2O3 hydrogel microspheres as enzyme supports through sol-gel transition using a solvent-in-oil emulsion. Cellulose-dissolving solvents including 1-ethyl-3-methylimidazolium ([Emim][Ac]), an aqueous mixture of NaOH and thiourea, tetrabutylammonium hydroxide, and tetrabutylphosphonium hydroxide were used to prepare regular shaped cellulose/Fe2O3 microspheres. The solvent affected microsphere characteristics like crystallinity, hydrophobicity, surface morphology, size distribution, and swelling properties. The immobilization efficiency of the microspheres for lipase was also significantly influenced by the type of cellulose solvent used. In particular, the lipase immobilized on cellulose/Fe2O3 microspheres prepared using [Emim][Ac] showed the highest protein loading, and its specific activity was 3.1-fold higher than that of free lipase. The immobilized lipase could be simply recovered by a magnet and continuously reused.

Improved Process to Obtain Nanofibrillated Cellulose (CNF) Reinforced Starch Films with Upgraded Mechanical Properties and Barrier Character

Nowadays, the interest on nanofibrillated cellulose (CNF) has increased owing to its sustainability and its capacity to improve mechanical and barrier properties of polymeric films. Moreover, this filler shows some drawbacks related with its high capacity to form aggregates, hindering its dispersion in the matrix. In this work, an improved procedure to optimize the dispersability of CNF in a thermoplastic starch was put forward. On the one hand, CNF needs a hydrophilic dispersant to be included in the matrix, and on the other, starch needs a hydrophilic plasticizer to obtain a thermoformable material. Glycerol was used to fulfil both targets at once. CNF was predispersed in the plasticizer before nanofibrillation and later on was included into starch, obtaining thin films. The tensile strength of these CNF–starch composite films was 60% higher than the plain thermoplastic starch at a very low 0.36% w/w percentage of CNF. The films showed a noticeable correlation between water uptake, and temperature and humidity. Regarding permeability, a ca. 55% oxygen and water vapor permeability drop was found by nanofiller loading. The hydrolytic susceptibility of the composite was confirmed, being similar to that of the thermoplastic starch.

Concentrated sulfuric acid aqueous solution enables rapid recycling of cellulose from waste paper into antimicrobial packaging

Waste paper is a major contributor to municipal and industrial waste, and its recycle and reuse are a current challenge. The aim of this research is to convert waste paper into value-added cellulose films through rapid dissolution in pre-cooled H₂SO₄ aqueous solution. Two types of waste paper, office paper and cardboard, could be dissolved within 210 s. The regenerated office paper films were transparent, and exhibited excellent mechanical properties (tensile strength: 77.55 ± 6.52 MPa, elongation at break: 2.67 ± 0.30 %, and Young's modulus: 5451.67 ± 705.23 MPa), which were comparable to those of cellulose films prepared from spruce pulp in the same solvent. The mixed paper films showed a dramatically reduced UV transmittance due to the existence of lignin. Moreover, the regenerated films were a promising matrix to load antimicrobial compounds, and thus inhibited the growth of pathogenic bacteria. Therefore, this work provides a convenient way to directly convert waste paper into biodegradable antimicrobial packaging materials.

Cellulose Nanocrystals Derived from Textile Waste through Acid Hydrolysis and Oxidation as Reinforcing Agent of Soy Protein Film

More than 10 million tons of textile waste are disposed through landfill every year in North America. The disposal of textile waste via landfill or incineration causes environmental problems and represents a waste of useful resources. In this work, we explored the possibility to directly extract cellulose nanocrystals (CNCs) from untreated textile waste through two methods, namely sulfuric acid hydrolysis and three-step oxidization. CNCs with cellulose I_β crystalline structure and rod-like shape were successfully obtained. The aspect ratios of CNCs prepared from acid hydrolysis and oxidization were 10.00 ± 3.39 and 17.10 ± 12.85, respectively. Their application as reinforcing agent of soybean protein isolate (SPI) film was evaluated. With the addition of 20% CNCs, the composite film maintained the high transparency, while their water vapor barrier property, tensile strength, and Young’s modulus were significantly improved. This research demonstrates a promising approach to recycle textile waste, and more value-added applications based on the derived CNCs could be expected.

Effect of the Anomeric Configuration on the Micellization of Hexadecylmaltoside Surfactants

The self-assembly of the two anomeric forms of n-hexadecyl-d-maltopyranoside (denoted α-C₁₆G₂ and β-C₁₆G₂) has been studied in dilute aqueous solution by means of surface tension measurements, scattering methods (dynamic light scattering, static light scattering, and small-angle X-ray and neutron scattering), and cryo-transmission electron microscopy at different surfactant concentrations and temperatures. Surface tension measurements demonstrate differences in the surfactant adsorption at the air-water interface, where α-C₁₆G₂ shows a lower CMC than β-C₁₆G₂. Similarly, micelle morphology was found to profoundly depend on anomerism. β-C₁₆G₂ preferentially forms very elongated micelles with large persistence lengths, whereas α-C₁₆G₂ assembles into smaller micelles for which the structure varies with concentration and temperature. The differences between the two surfactant anomers in terms of self-assembly can be attributed to the interaction between neighboring headgroups. Specifically, β-C₁₆G₂ allows for a closer packing in the palisade layer, hence reducing the micelle curvature and promoting the formation of more elongated micelles. Strong intermolecular headgroup interactions may also account for the observed rigidity of the micelles.

Composites of nanofibrillated cellulose with clay minerals: A review

Biopolymers-based composites are, in general, environmentally friendly materials, which can be obtained from renewable sources. Some of them can also present promising properties to be used in food packaging and electronic devices, being thus logical substitutes to petroleum-based polymers, specifically plastics. Cellulose nanofibrils (CNF) obtained by chemical/enzymatic pre-treatments followed by a mechanical treatment appear as a new suitable biomaterial. However, CNF are still quite expensive materials, due to the required chemicals/equipment/energy involved, and additionally, they present some limitations such as high hydrophilicity/high water vapour permeability. The combination of CNF with clay minerals, such as montmorillonite or kaolinite, as widely available geo-resources, represents an excellent way to reduce the amount of CNF used, enabling the production of valuable materials and reducing costs; and, at the same time it is possible to improve the characteristics of the formed materials, such as mechanical, gas barrier and fire retardancy properties, if appropriate conditions of preparation are used. Nevertheless, to obtain hybrid CNF/clay composites with superior properties it is necessary to ensure a good dispersion of the inorganic material in the CNF suspension and a good compatibility among the inorganic and organic components. To fulfil this goal, several strategies can be considered, including physical treatments of the suspensions, CNF and clay surface chemical modifications, and the use of a coupling agent. In this review article, the state-of-the-art on a new emerging generation of composites (films, foams or coatings) based on nanofibrillated cellulose and nanoclay, with focus on strategies for their preparation and most relevant achievements is critically reviewed, bearing in mind their potential application as substitutes for common plastics. A third component has been eventually added to these organic-inorganic hybrids, e.g., chitosan, carboxymethylcellulose, borate or epoxy resin, to enhance specific characteristics of the material. Some general background on the production of different types of CNF and their main properties is previously provided.

Emulsion Formation and Stabilization by Biomolecules: The Leading Role of Cellulose

Emulsion stabilization by native cellulose has been mainly hampered because of its insolubility in water. Chemical modification is normally needed to obtain water-soluble cellulose derivatives. These modified celluloses have been widely used for a range of applications by the food, cosmetic, pharmaceutic, paint and construction industries. In most cases, the modified celluloses are used as rheology modifiers (thickeners) or as emulsifying agents. In the last decade, the structural features of cellulose have been revisited, with particular focus on its structural anisotropy (amphiphilicity) and the molecular interactions leading to its resistance to dissolution. The amphiphilic behavior of native cellulose is evidenced by its capacity to adsorb at the interface between oil and aqueous solvent solutions, thus being capable of stabilizing emulsions. In this overview, the fundamentals of emulsion formation and stabilization by biomolecules are briefly revisited before different aspects around the emerging role of cellulose as emulsion stabilizer are addressed in detail. Particular focus is given to systems stabilized by native cellulose, either molecularly-dissolved or not (Pickering-like effect).

Molecular insight into the wetting behavior and amphiphilic character of cellulose nanocrystals

The study of nanocellulose is a field of growing interest due to its many applications and its use in the development of biocompatible and eco-friendly materials. In spite of the vast number of studies in the field, many questions about the role of the molecular structure in the properties of cellulose are still subject of debate. One of these fundamental questions is the possible amphiphilic nature of cellulose and the relative role of hydrogen bonding and hydrophobic effect on the interactions of cellulose. In this work we present an extensive molecular dynamics simulation study of this question by analyzing the wetting of cellulose with water and organic solvent, its interaction with hydrophilic and hydrophobic ions and its interaction with a protein (human epidermal growth factor, hEGF). We consider two characteristic cellulose crystal planes of Iβ cellulose with very different roughness, different hydrogen bonding capability and different exposure of cellulose hydrophobic groups (the (010) plane which has exposed -OH groups and the (100) plane with buried -OH groups). Our results show that both surfaces are simultaneously hydrophilic and lipophilic, with both surfaces having very similar contact angles. In spite of the global similarity of wetting of both surfaces, the molecular details of wetting are very different and substantial local wetting heterogeneities (which strongly depend on the surface) appear for both solvents. We also observe a weak interaction of both surfaces with hydrophobic and hydrophilic solutes. These weak interactions are attributed to the simultaneous lipophilic and hydrophilic character of both (100) and (010) cellulose surfaces. Interestingly, we found a substantial interaction of both cellulose planes with polar and apolar residues of the hEGF protein.

New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali

The gelation of cellulose in alkali solutions is quite relevant, but still a poorly understood process. Moreover, the role of certain additives, such as urea, is not consensual among the community. Therefore, in this work, an unusual set of characterization methods for cellulose solutions, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR) and diffusion wave spectroscopy (DWS) were employed to study the role of urea on the dissolution and gelation processes of cellulose in aqueous alkali. Cryo-TEM reveals that the addition of urea generally reduces the presence of undissolved cellulose fibrils in solution. These results are consistent with PTssNMR data, which show the reduction and in some cases the absence of crystalline portions of cellulose in solution, suggesting a pronounced positive effect of the urea on the dissolution efficiency of cellulose. Both conventional mechanical macrorheology and microrheology (DWS) indicate a significant delay of gelation induced by urea, being absent until ca. 60 °C for a system containing 5 wt % cellulose, while a system without urea gels at a lower temperature. For higher cellulose concentrations, the samples containing urea form gels even at room temperature. It is argued that since urea facilitates cellulose dissolution, the high entanglement of the cellulose chains in solution (above the critical concentration, C*) results in a strong three-dimensional network.

Structural Analysis of Cellulose-Coated Oil-in-Water Emulsions Fabricated from Molecular Solution

Natural cellulose has been used as a coating to stabilize oil-in-water (o/w) emulsions by exploiting the amphiphilic character of the cellulose chains molecularly dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate. Its cellulose coating exhibits a continuous amorphous structure which differs significantly from the cellulose particle stabilization used in Pickering emulsions. The structure of these cellulose-coated o/w emulsion particles, in particular the cellulose coating shell characteristics (thickness, porosity, and composition), is studied by using a combination of direct imaging methods such as cryogenic electron microscopy and fluorescence microscopy with small-angle neutron scattering measurements. This work suggests a unique multicompartment structure of the emulsion particles: an oil core, surrounded by an inner shell composed of a porous cellulose gel, encapsulated by a dense outer cellulose shell, a few nanometers in thickness. The thickness of the inner cellulose shell varies significantly. The nanoscale emulsion droplets exhibit a thickness of 10 ± 3 nm, whereas the larger micron-sized droplets exhibit a thicker inner cellulose shell of 500-750 nm. It is also inferred that the cellulose shells contain water rather than oil.

Statistical thermodynamics unveils the dissolution mechanism of cellobiose

Statistical thermodynamic analysis of cellobiose solubility in aqueous salts sheds light on the mechanism of cellulose solubilization on a molecular scale.

Ionization of Cellobiose in Aqueous Alkali and the Mechanism of Cellulose Dissolution

Cellulose, one of the most abundant renewable resources, is insoluble in most common solvents but dissolves in aqueous alkali under a narrow range of conditions. To elucidate the solubilization mechanism, we performed electrophoretic NMR on cellobiose, a subunit of cellulose, showing that cellobiose acts as an acid with two dissociation steps at pH 12 and 13.5. Chemical shift differences between cellobiose in NaOH and NaCl were estimated using 2D NMR and compared to DFT shift differences upon deprotonation. The dissociation steps are the deprotonation of the hemiacetal OH group and the deprotonation of one of four OH groups on the nonreducing anhydroglucose unit. MD simulations reveal that aggregation is suppressed upon charging cellulose chains in solution. Our findings strongly suggest that cellulose is to a large extent charged in concentrated aqueous alkali, a seemingly crucial factor for solubilization. This insight, overlooked in the current literature, is important for understanding cellulose dissolution and for synthesis of new sustainable materials.

From surfactant to cellulose and DNA self-assembly. A 50-year journey

Surfactants have been the basis for applications in several industrial sectors for a long time. However, fundamental research was 50 years ago still limited to a small number of academic groups and even basic aspects were controversial. The field has since undergone an enormous expansion and the improved understanding has laid the basis of numerous new products as well as been the basis of important parts of nano-science and -technology.The present author has during 50 years in academia devoted most of his research to amphiphilic compounds, including both surfactants and polymers. Hereby, I had the privilege of following a very exciting development. In 2015, I had the honour to receive the Life-time Achievement Award of IACIS, the International Association of Colloid and Interface Scientists. IACIS organizes since the 1970s a tri-annual symposium, typically the best attended in the field. For the first time since 2000, it was in 2015 organized in Europe, namely Mainz, Germany. This treatise is based on my award lecture in Mainz, which covered developments from my first research as a new Ph D student in Stockholm to current work as an emeritus and visiting professor. Interestingly, discoveries in my very early work contributed to solving problems in now on-going research. Håkan Wennerström kindly wrote a quite comprehensive paper about my achievements a few years ago (Adv Colloid Interf Sci 205:1-8, [1]). In writing the present paper, I have strived at covering mainly topics not treated in detail by Håkan. In fact, I will emphasize very much our early studies as well as our studies of surfactant self-assembly by NMR and in particular look at the developments of our research and connections between different research topics.

On the dissolution state of cellulose in aqueous tetrabutylammonium hydroxide solutions

We have characterized the dissolution state of microcrystalline cellulose (MCC) in aqueous 40 wt% tetrabutylammonium hydroxide (TBAH) using a combination of light and small angle X-ray scattering, up to 0.1 g cm⁻³.