Browsing by Author "Rosenau, Thomas"

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2D Assignment and quantitative analysis of cellulose and oxidized celluloses using solution-state NMR spectroscopy
(2020-09-01) Koso, Tetyana; Rico del Cerro, Daniel; Heikkinen, Sami; Nypelö, Tiina; Buffiere, Jean; Perea-Buceta, Jesus E.; Potthast, Antje; Rosenau, Thomas; Heikkinen, Harri; Maaheimo, Hannu; Isogai, Akira; Kilpeläinen, Ilkka; King, Alistair W.T.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The limited access to fast and facile general analytical methods for cellulosic and/or biocomposite materials currently stands as one of the main barriers for the progress of these disciplines. To that end, a diverse set of narrow analytical techniques are typically employed that often are time-consuming, costly, and/or not necessarily available on a daily basis for practitioners. Herein, we rigorously demonstrate a general quantitative NMR spectroscopic method for structural determination of crystalline cellulose samples. Our method relies on the use of a readily accessible ionic liquid electrolyte, tetrabutylphosphonium acetate ([P-4444][OAc]):DMSO-d(6), for the direct dissolution of biopolymeric samples. We utilize a series of model compounds and apply now classical (nitroxyl-radical and periodate) oxidation reactions to cellulose samples, to allow for accurate resonance assignment, using 2D NMR. Quantitative heteronuclear single quantum correlation (HSQC) was applied in the analysis of key samples to assess its applicability as a high-resolution technique for following cellulose surface modification. Quantitation using HSQC was possible, but only after applying T(2)correction to integral values. The comprehensive signal assignment of the diverse set of cellulosic species in this study constitutes a blueprint for the direct quantitative structural elucidation of crystalline lignocellulosic, in general, readily available solution-state NMR spectroscopy. [GRAPHICS] .
Assembling Native Elementary Cellulose Nanofibrils via a Reversible and Regioselective Surface Functionalization
(2021-10-20) Beaumont, Marco; Tardy, Blaise L.; Reyes, Guillermo; Koso, Tetyana V.; Schaubmayr, Elisabeth; Jusner, Paul; King, Alistair W.T.; Dagastine, Raymond R.; Potthast, Antje; Rojas, Orlando J.; Rosenau, Thomas
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Selective surface modification of biobased fibers affords effective individualization and functionalization into nanomaterials, as exemplified by the TEMPO-mediated oxidation. However, such a route leads to changes of the native surface chemistry, affecting interparticle interactions and limiting the development of potential supermaterials. Here we introduce a methodology to extract elementary cellulose fibrils by treatment of biomass with N-succinylimidazole, achieving regioselective surface modification of C6-OH, which can be reverted using mild post-treatments. No polymer degradation, cross-linking, nor changes in crystallinity occur under the mild processing conditions, yielding cellulose nanofibrils bearing carboxyl moieties, which can be removed by saponification. The latter offers a significant opportunity in the reconstitution of the chemical and structural interfaces associated with the native states. Consequently, 3D structuring of native elementary cellulose nanofibrils is made possible with the same supramolecular features as the biosynthesized fibers, which is required to unlock the full potential of cellulose as a sustainable building block.
Assessing Fire-Damage in Historical Papers and Alleviating Damage with Soft Cellulose Nanofibers
(2022-04) Völkel, Laura; Beaumont, Marco; Johansson, Leena-Sisko; Czibula, Caterina; Rusakov, Dmitrii; Mautner, Andreas; Teichert, Christian; Kontturi, Eero; Rosenau, Thomas; Potthast, Antje
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The conservation of historical paper objects with high cultural value is an important societal task. Papers that have been severely damaged by fire, heat, and extinguishing water, are a particularly challenging case, because of the complexity and severity of damage patterns. In-depth analysis of fire-damaged papers, by means of examples from the catastrophic fire in a 17th-century German library, shows the changes, which proceeded from the margin to the center, to go beyond surface charring and formation of hydrophobic carbon-rich layers. The charred paper exhibits structural changes in the nano- and micro-range, with increased porosity and water sorption. In less charred areas, cellulose is affected by both chain cleavage and cross-linking. Based on these results and conclusions with regard to adhesion of auxiliaries, a stabilization method is developed, which coats the damaged paper with a thin layer of cellulose nanofibers. It enables the reliable preservation of the paper and—most importantly—retrieval of the contained historical information: the nanofibers form a flexible, transparent film on the surface and adhere strongly to the damaged matrix, greatly reducing its fragility, giving it stability, and enabling digitization and further handling.
Ball milling’s effect on pine milled wood lignin’s structure and molar mass
(2018-09-01) Zinovyev, Grigory; Sumerskii, Ivan; Rosenau, Thomas; Balakshin, Mikhail; Potthast, Antje
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The effect of ball milling expressed as the yield of milled wood lignin (MWL) on the structure and molar mass of crude milled wood lignin (MWLc) preparation is studied to better understand the process’ fundamentals and find optimal conditions for MWL isolation (i.e., to obtain the most representative sample with minimal degradation). Softwood (loblolly pine) MWLc preparations with yields of 20–75% have been isolated and characterized based on their molar mass distribution (by Size Exclusion Chromatography (SEC)), hydroxyl groups of different types (31P NMR), methoxyl groups (HS-ID GC-MS), and sugar composition (based on methanolysis). Classical MWL purification is not used to access the whole extracted lignin. The results indicate that lignin degradation during ball milling occurs predominantly in the high molar mass fraction and is less pronounced in the low molar mass fraction. This results in a significant decrease in the Mz and Mw of the extracted MWLc with an increase in the yield of MWLc, but has only a very subtle effect on the lignin structure if the yield of MWLc is kept below about 55%. Therefore, no tedious optimization of process variables is necessary to achieve the required MWLc yield in this range for structural studies of softwood MWL. The sugar composition shows higher amounts of pectin components in MWLs of low yields and higher amounts of glucan and mannan in high-yield MWLs, confirming that lignin extraction starts from the middle lamella in the earlier stages of MWL isolation, followed by lignin extraction from the secondary wall region.
Cyclic peroxides as key intermediates in the degradation of cellulosic key chromophores by alkaline hydrogen peroxide: first direct proof by 17O NMR
(2018-06-01) Bacher, Markus; Hosoya, Takashi; Zwirchmayr, Nele Sophie; Nomura, Satoshi; Gille, Lars; Dietz, Thomas; Erata, Tomoki; Potthast, Antje; Vuorinen, Tapani; Rosenau, Thomas
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Abstract: 2,5-Dihydroxy-[1,4]-benzoquinone (DHBQ) and 5,8-dihydroxy-[1,4]-naphthoquinone (DHNQ) are two key chromophores which are almost ubiquitous in cellulosic materials. Their fate under conditions of alkaline peroxide bleaching (P stage) has been established previously, but the intermediacy of cyclic peroxides, which so far had only been postulated, remained an open issue. By means of 17O NMR spectroscopy, additionally supported by other NMR techniques, it was demonstrated that both DHBQ and DHNQ form cyclic peroxides as primary intermediates in the reaction with hydrogen peroxide under alkaline conditions. These intermediates are subsequently further degraded to products already known. The experimental confirmation of the cyclic peroxides is an important step in the understanding of reaction mechanisms in pulp bleaching chemistry. Graphical Abstract: [Figure not available: see fulltext.].
Debugging periodate oxidation of cellulose: Why following the common protocol of quenching excess periodate with glycol is a bad idea
(2023-06-15) Simon, Jonas; Fliri, Lukas; Drexler, Felix; Bacher, Markus; Sapkota, Janak; Ristolainen, Matti; Hummel, Michael; Potthast, Antje; Rosenau, Thomas
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Periodate oxidation of cellulose to produce “dialdehyde cellulose” (DAC) has lately received increasing attention in sustainable materials development. Despite the longstanding research interest and numerous reported studies, there is still an enormous variation in the proposed preparation and work-up protocols. This apparently reduces comparability and causes reproducibility problems in DAC research. Two simple but prevalent work-up protocols, namely glycol quenching and filtration/washing, were critically examined and compared, resulting in this cautionary note. Various analytical techniques were applied to quantify residual iodine species and organic contaminations from quenching side reactions. The commonly practiced glycol addition cannot remove all oxidising iodine compounds. Both glycol and the formed formaldehyde are incorporated into DAC's polymeric structure. Quenching of excess periodate with glycol can thus clearly be discouraged. Instead, simple washing protocols are recommended which do not bear the risk of side reactions with organic contaminants. While simple washing was sufficient for mildly oxidised celluloses, higher oxidised samples were more likely to trap residual (per)iodate, as determined by thiosulfate titration. For work-up, simple washing with water is proposed while determining potential iodine contaminations after washing with a simple colorimetric test and, if needed, removal of residual periodate by washing with an aqueous sodium thiosulfate solution.
Exploring Alkyl-O-Alkyl Ether Structures in Softwood Milled Wood Lignins
(2023-01-11) Zhu, Xuhai; Sipilä, Jussi; Potthast, Antje; Rosenau, Thomas; Balakshin, Mikhail
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Recent studies have suggested that there are significant amounts of various alkyl ether (Alk-O-Alk; Alk = alkyl) moieties in a spruce native lignin preparation, milled wood lignin (SMWL). However, the comprehensive NMR assignment to these moieties has not been addressed yet. This study focused on investigating different types of Alk-O-Alk structures at the α- and γ-positions of the lignin side chain in an heteronuclear single-quantum coherence (HSQC) spectrum of SMWL using experimental NMR data of lignin and synthesized model compounds. Ambiguous structural features were predicted by computer simulation of 1H and 13C NMR spectra to complement the experimental NMR data. As a result, specific regions in the HSQC spectrum were attributed to different Alk-O-Alk moieties of Alk-O-Alk/β-O-4 and Alk-O-Alk/β-β′ structures. However, the differences between the specific regions were rather subtle; they were not well separated from each other and some major lignin moieties. Furthermore, SMWL contained a large variety of Alk-O-Alk moieties but in minute individual amounts, resulting in rather broad, superimposing resonances. Thus, evaluation did not allow assigning individual types of Alk-O-Alk moieties from the HSQC spectra; instead, they were quantified as total (α- and γ-linked) Alk-O-Alk based on the balance of structural units in the 13C NMR spectra. At last, potential formation mechanisms of various Alk-O-Alk ether structures in lignin biosynthesis, lignin aging, and during ball milling of wood were hypothesized and discussed.
Indirect determination of partial depolymerization reactions in dialdehyde celluloses (DAC) by gel permeation chromatography of their oxime derivatives
(2023-09) Fliri, Lukas; Simon, Jonas; Sulaeva, Irina; Rosenau, Thomas; Potthast, Antje; Hummel, Michael
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Owing to a supposed quantitative transformation, oximation of dialdehyde cellulose (DAC) with hydroxylamine hydrochloride is commonly employed in chemical DAC analysis, e.g., for the determination of the degree of oxidation (DO) by titration or elemental analysis. In this study, this modification was utilized for the indirect determination of molecular weight distributions (MWD) by gel permeation chromatography (GPC). The presumably quantitative conversion of aldehyde groups in DAC to the corresponding oxime also breaks up the intermolecular and intramolecular hemiacetal crosslinks, which were associated with solubility issues in the DMAc/LiCl solvent system in previous studies. The limits of the procedure and the material's stability during oximation were investigated. For samples with a DO up to approximately 9% a good applicability was observed, before at higher DO values residual crosslinks led to solubility problems. The oximation/GPC protocol was used to examine the development of the MWD in the early stages of DAC formation under different reaction conditions. The time-dependent partial depolymerization of the polymer backbone was observed. Furthermore, the stability of DAC towards different pH conditions ranging from strongly acidic to strongly alkaline was tested. The depolymerization of DAC in alkaline media occurred with concomitant degradation of aldehyde moieties. In turn, DAC proved to be remarkably stable in acidic and neutral solutions up to a pH of 7.
Insights into the borohydride reduction of dialdehyde cellulose: the dilemma of competing reduction and β-elimination reactions
(2023-09) Simon, Jonas; Fliri, Lukas; Fröhlich, Flavia; Sapkota, Janak; Ristolainen, Matti; Hummel, Michael; Rosenau, Thomas; Potthast, Antje
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Borohydride reduction of dialdehyde cellulose (DAC) is a promising strategy to generate dialcohol cellulose as bio-based alternative to petroleum-based materials. However, the degradation of the polymer backbone according to β-elimination mechanisms limits the practical applications of the reaction. Therefore, we aimed at optimizing the process to suppress degradation reactions by varying reaction time, pH, and reagent stoichiometry. The degree of oxidation (DO) of the DAC intermediates significantly impacts the yields and molecular weights of the isolated dialcohol celluloses, with a “leveling-off” effect at higher DO values. Increasing the amount of sodium borohydride can minimize—but not entirely prevent—chain scissions. Lowering the pH value during reduction slows down the degradation but results in incomplete conversion of the aldehyde functionalities. Our study provides valuable insights into the consequences of side reactions during borohydride reduction of DAC as well as into chemistry and analysis of the dialdehyde cellulose/dialcohol cellulose system. Graphical abstract: About a dilemma in cellulose chemistry: Dialcohol cellulose derived by periodate oxidation and subsequent borohydride reduction of cellulose has received increasing attention in the development of sustainable thermoplastic materials. The present study highlights the challenge of suppressing β-elimination and favoring the reduction pathway to optimize reaction conditions and minimize chain degradation.
Manufacturing heat-damaged papers as model materials for evaluating conservation methods
(2022-07) Völkel, Laura; Rusakov, Dmitrii; Kontturi, Eero; Beaumont, Marco; Rosenau, Thomas; Potthast, Antje
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Direct fire, indirect heat, and extinguishing water cause great damage to cultural assets upon a fire disaster in a library or archive. Conservation and restoration of heat-damaged papers are particularly challenging due to the complexity and severity of the damage. Since valuable originals obviously cannot be used for the development of treatment methods and only to a limited extent for the analysis of the damage, it is necessary to produce model paper materials that have a high degree of similarity to fire-damaged papers, which was addressed in the present study. Three different heating methods were tested to produce model papers of different heating levels. Their altered optical, structural, and chemical properties were analyzed and compared with the results of original fire-damaged samples. The study points out pathways to enable the production of comparable sample materials. Heating between hot plates or in an oven produces papers that have properties quite similar to the originals in terms of surface area, paper structure, cellulose integrity, and interactions with water. Stack heating in the oven has proven to be a particularly effective manufacturing method for larger quantities of model papers.
A mechanistic study on the alleged cellulose cross-linking system: Maleic acid/sodium hypophosphite
(2024-12-15) Lehrhofer, Anna F.; Fliri, Lukas; Bacher, Markus; Budischowsky, David; Sulaeva, Irina; Hummel, Michael; Rosenau, Thomas; Hettegger, Hubert
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
A combination of maleic acid and sodium hypophosphite as a durable press finishing agent has been reported as a safer but equally effective alternative to conventional formaldehyde-based cross-linking agents for applications in cellulose-based fiber and textile finishing. However, the mechanistic details of this system have not yet been fully elucidated to allow optimization of the conditions. Effective cross-linking treatment requires high curing temperatures of ≥160 °C, which enhances oxidative and thermal degradation of cellulose. In this work, the sequential steps of the cross-linking mechanism were investigated both with model compounds and cellulosic substrates. Extensive NMR studies on model compounds revealed several side reactions alongside the synthesis of the targeted cross-linkable moiety. As an alternative, to circumvent side reactions, a two-step procedure was used by synthesizing the cross-linker sodium 2-[(1,2-dicarboxyethyl)phosphinate]succinic acid in a well-defined pre-condensation reaction before application onto the cellulosic substrate. Further, the effect of the cross-linking treatment on the molecular weight distribution of cellulose was studied by gel permeation chromatography, which showed degradation due to maleic acid/sodium hypophosphite treatment. By using sodium 2-[(1,2-dicarboxyethyl)phosphinate]succinic acid and sodium hypophosphite, this degradation could be significantly limited.
N-Alkylated Chitin Nanocrystals as a Collector in Malachite Flotation
(2022-08-15) Hartmann, Robert; Beaumont, Marco; Pasquier, Eva; Rosenau, Thomas; Serna-Guerrero, Rodrigo
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The majority of reagents currently used in mineral flotation processes are fossil-based and potentially harmful to the environment. Therefore, it is necessary to find environmentally-friendly alternatives to reduce the impact of mineral processing activities. Chitin nanocrystals are a renewable resource that, due to the natural presence of amino groups on its surface, represents a promising collector for various minerals of economic relevance. This study examines the one-pot functionalization of chitin nanocrystals with aldehyde structures to obtain hydrophobized colloids suitable for mineral flotation. The chemical properties of these nano-colloids were investigated by nuclear magnetic resonance spectroscopy, their colloidal behavior and structure by electrophoretic light scattering and atomic force microscopy, and their wettability through water contact angle measurements. The functionalized N-alkylated chitin nanocrystals possessed a hydrophobic character, were able to dress mineral particles and featured a performance in the flotation of malachite similar to commercial collectors, which proves the high potential of chitin nanocrystals in this field of application.
New Opportunities in the Valorization of Technical Lignins
(2021-02-18) Balakshin, Mikhail Yu; Capanema, Ewellyn A.; Sulaeva, Irina; Schlee, Philipp; Huang, Zeen; Feng, Martin; Borghei, Maryam; Rojas, Orlando J.; Potthast, Antje; Rosenau, Thomas
A2 Katsausartikkeli tieteellisessä aikakauslehdessä
Sugar-based biorefineries have faced significant economic challenges. Biorefinery lignins are often classified as low-value products (fuel or low-cost chemical feedstock) mainly due to low lignin purities in the crude material. However, recent research has shown that biorefinery lignins have a great chance of being successfully used as high-value products, which in turn should result in an economy renaissance of the whole biorefinery idea. This critical review summarizes recent developments from our groups, along with the state-of-the-art in the valorization of technical lignins, with the focus on biorefinery lignins. A beneficial synergistic effect of lignin and cellulose mixtures used in different applications (wood adhesives, carbon fiber and nanofibers, thermoplastics) has been demonstrated. This phenomenon causes crude biorefinery lignins, which contain a significant amount of residual crystalline cellulose, to perform superior to high-purity lignins in certain applications. Where previously specific applications required high-purity and/or functionalized lignins with narrow molecular weight distributions, simple green processes for upgrading crude biorefinery lignin are suggested here as an alternative. These approaches can be easily combined with lignin micro-/nanoparticles (LMNP) production. The processes should also be cost-efficient compared to traditional lignin modifications. Biorefinery processes allow much greater flexibility in optimizing the lignin characteristics desirable for specific applications than traditional pulping processes. Such lignin engineering, at the same time, requires an efficient strategy capable of handling large datasets to find correlations between process variables, lignin structures and properties and finally their performance in different applications.
A note on the chemical fate of the DABCO catalyst in amine-catalyzed hypochlorite bleaching of cellulosic pulps
(2024-05) Lehrhofer, Anna F.; Isaza Ferro, Estefania; Hosoya, Takashi; Hettegger, Hubert; Vuorinen, Tapani; Rosenau, Thomas
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Hypochlorous acid bleaching under amine catalysis (Hcat bleaching stage) is an optimized bleaching stage variant that is characterized by working at weakly acidic, near-neutral pH, having high bleaching efficiency, and discharging only very small amounts of chloro-organics. This study addressed the chemical fate of the used 1,4-diazabicyclo[2.2.2]octane (DABCO) catalyst. While literature proposed either homolytic or heterolytic breakage of one ethylene bridge and subsequent release of the resulting fragments as two molecules of formaldehyde, we demonstrated the degradation to proceed by ionic elimination of one ethylene bridge starting from mono-N-chlorinated DABCO. The resulting N-vinyl (enamine) derivative adds water under the release of acetaldehyde and formation of piperazine. The generation of acetaldehyde was experimentally confirmed by 2,4-dinitrophenylhydrazine trapping, directly from the processing liquid. The experimental findings agreed superbly with computations which showed the “acetaldehyde mechanism” to be much favored over the previously proposed pathways under C–C bond cleavage and release of formaldehyde. The results of this study add to a better understanding of the novel Hcat bleaching system. Graphical abstract: (Figure presented.).
A novel approach to analyze the impact of lytic polysaccharide monooxygenases (LPMOs) on cellulosic fibres
(2024-03-15) Sulaeva, Irina; Budischowsky, David; Rahikainen, Jenni; Marjamaa, Kaisa; Støpamo, Fredrik Gjerstad; Khaliliyan, Hajar; Melikhov, Ivan; Rosenau, Thomas; Kruus, Kristiina; Várnai, Anikó; Eijsink, Vincent G.H.; Potthast, Antje
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Enzymatic treatment of cellulosic fibres is a green alternative to classical chemical modification. For many applications, mild procedures for cellulose alteration are sufficient, in which the fibre structure and, therefore, the mechanical performance of cellulosic fibres are preserved. Lytic polysaccharide monooxygenases (LPMOs) bear a great potential to become a green reagent for such targeted cellulose modifications. An obstacle for wide implementation of LPMOs in tailored cellulose chemistry is the lack of suitable techniques to precisely monitor the LPMO impact on the polymer. Soluble oxidized cello-oligomers can be quantified using chromatographic and mass-spectrometric techniques. A considerable portion of the oxidized sites, however, remain on the insoluble cellulose fibres, and their quantification is difficult. Here, we describe a method for the simultaneous quantification of oxidized sites on cellulose fibres and changes in their molar mass distribution after treatment with LPMOs. The method is based on quantitative, heterogeneous, carbonyl-selective labelling with a fluorescent label (CCOA) followed by cellulose dissolution and size-exclusion chromatography (SEC). Application of the method to reactions of seven different LPMOs with pure cellulose fibres revealed pronounced functional differences between the enzymes, showing that this CCOA/SEC/MALS method is a promising tool to better understand the catalytic action of LPMOs.
Recent achievements in the valorization of technical lignins
(2018) Balakshin, Mikhail; Capanema, Ewellyn A.; Huang, Zeen; Sulaeva, Irina; Rojas, Orlando; Feng, Martin; Rosenau, Thomas; Potthast, Antje
A4 Artikkeli konferenssijulkaisussa
Reductive Amination of Dialdehyde Cellulose: Access to Renewable Thermoplastics
(2023-01-09) Simon, Jonas; Fliri, Lukas; Sapkota, Janak; Ristolainen, Matti; Miller, Stephen A.; Hummel, Michael; Rosenau, Thomas; Potthast, Antje
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The reductive amination of dialdehyde cellulose (DAC) with 2-picoline borane was investigated for its applicability in the generation of bioderived thermoplastics. Five primary amines, both aliphatic and aromatic, were introduced to the cellulose backbone. The influences of the side chains on the course of the reaction were examined by various analytical techniques with microcrystalline cellulose as a model compound. The obtained insights were transferred to a 39%-oxidized softwood kraft pulp to study the thermal properties of thereby generated high-molecular-weight thermoplastics. The number-average molecular weights (Mn) of the diamine celluloses, ranging from 60 to 82 kD, were investigated by gel permeation chromatography. The diamine celluloses exhibited glass transition temperatures (Tg) from 71 to 112 °C and were stable at high temperatures. Diamine cellulose generated from aniline and DAC showed the highest conversion, the highest Tg (112 °C), and a narrow molecular weight distribution (Døµ of 1.30).
Soft cellulose II nanospheres: Sol-gel behaviour, swelling and material synthesis
(2019-10-14) Beaumont, Marco; Rosenfeldt, Sabine; Tardy, Blaise L.; Gusenbauer, Claudia; Khakalo, Alexey; Nonappa; Opietnik, Martina; Potthast, Antje; Rojas, Orlando J.; Rosenau, Thomas
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
High axial aspect crystalline nanomaterials have emerged as polymeric building blocks for the construction of supermaterials. In contrast to this form, amorphous nanospheres have remained largely untapped. This is especially peculiar in the context of material assembly, due to the wide range of opportunities they offer by virtue of their soft particle characteristics, high volume ratio at low solid content and their highly swollen and accessible structure. In the context of cellulose, these colloids represent a new field in the family of nanocelluloses. We report an organic solvent-free, heterogeneous and simple synthesis of spherical carboxylated nanoparticles bearing a distinctive, amorphous outer shell structure. The particle shape is evaluated by atomic force microscopy, cryo-transmission electron microscopy, dynamic light scattering and small-angle X-ray scattering. The soft shell structure of the particles and their responsiveness to ionic strength and pH are quantified by the combination of quartz-crystal microgravimetry and atomic force microscopy. Aqueous dispersions of the nanocolloids feature distinctive sol/gel behaviour: At solid content <2 wt% they behave as a low viscous liquid (sol state), whereas at higher concentrations the shells dominate the interparticle interactions, causing an exponential increase in viscosity, typical of a gel state (hydrogel). Gelation is reversible and can be triggered alternatively by protonation of the carboxylate groups under acidic conditions. Supercritical drying of the hydrogels yields a highly porous, isotropic aerogel composed of aggregated nanoparticles. In contrast, ambient drying results in an anisotropic, fully transparent film. These colloids will allow the study of the interaction between soft cellulose and rigid matter, and have high potential as toughening additives in composites. Furthermore, the amorphous nature of this new class of cellulose nanocolloids makes them attractive as support materials for catalysts and enzymes.
Spruce milled wood lignin : Linear, branched or cross-linked?
(2020-07-07) Balakshin, Mikhail; Capanema, Ewellyn Augsten; Zhu, Xuhai; Sulaeva, Irina; Potthast, Antje; Rosenau, Thomas; Rojas, Orlando J.
A2 Katsausartikkeli tieteellisessä aikakauslehdessä
The subject of lignin structure, critical for fundamental and practical reasons, is addressed in this study that includes a review of the methods applied to elucidate macromolecular branching. The recently available approaches for determination of the absolute molecular mass of spruce milled wood lignin (MWL) along with the quantification of terminal groups clearly indicate that MWL is significantly branched and cross-linked (with ∼36% lignin units partaking in these linkages). Results from independent methods imply that about half of the branching and crosslinking linkages involve aromatic rings, predominantly 5-5′ etherified units; meanwhile, a significant number of linkages are located in the side chains. Quantitative 13C NMR analyses suggest that the branches involve different aliphatic ether (alkyl-O-alkyl) types at the α- and γ-positions of the side chain, with intact β-O-4 linkages. While the exact structures of these moieties require further investigation, our results point to the fact that conventional lignification theory disagrees with the presence of such key moieties in softwood MWL and the observed high degree of branching/crosslinking. Potential reasons for the noted discrepancies are discussed. This journal is
Towards Tailored Dialdehyde Cellulose Derivatives: A Strategy for Tuning the Glass Transition Temperature
(2024-03-08) Simon, Jonas; Schlapp-Hackl, Inge; Sapkota, Janak; Ristolainen, Matti; Rosenau, Thomas; Potthast, Antje
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The derivatization of dialdehyde cellulose (DAC) has received increasing attention in the development of sustainable thermoplastics. In this study, a series of dialcohol celluloses were generated by borohydride reduction, which exhibited glass transition temperature (Tg) values ranging from 23 to 109 °C, depending on the initial degree of oxidation (DO) of the DAC intermediate. However, the DAC derivatives did not exhibit thermoplastic behavior when the DO of the modified DAC was below 26 %. The influence of introduced side chains was highlighted by comparing DAC-based thermoplastic materials obtained by either oximation or borohydride reduction. Our results provide insights into the generation of DAC-based thermoplastics and highlight a strategy for tailoring the Tg by adjusting the DO during the periodate oxidation step and selecting appropriate substituents in subsequent modifications.