Browsing by Author "Hietala, Sami"

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  • Adsorption study on the formation of interfacial layers based on birch glucuronoxylans
    (2024-09-01) Abik, Felix; Solin, Katariina; Hietala, Sami; Rojas, Orlando J.; Ho, Thao Minh; Mikkonen, Kirsi S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Glucuronoxylans (GX), particularly crude fractions obtained by pressurized hot water extraction of birch wood, act as potent emulsifiers and stabilizers against physical separation and lipid oxidation. Herein, we studied the adsorption of GX on hydrophobic interfaces to correlate their multicomponent character towards the formation of interfacial layers in emulsions. Dynamic interfacial tension (DIFT) and quartz crystal microgravimetry with dissipation monitoring (QCM-D) were applied to various GX fractions and the results compared with those from cellulose-based emulsifiers. The roles of residual lignin and polysaccharides are discussed considering the formation of interfacial layers during emulsification. The DIFT of the different GXs reached quasi-equilibrium faster as the lignin concentration increased, implying a correlation between the rate of adsorption and the residual lignin content. The effect of NaCl addition was more pronounced in polysaccharide-rich fractions, indicating that the polysaccharide fraction modulated the effect of ionic strength. QCM-D showed that despite the fast adsorption exhibited by the lignin-rich GX extract in the DIFT curves, the adsorbed materials were lightweight, suggesting that the polysaccharide fraction built the bulk of the interfacial layer. These results provide a foundation towards understanding the role of GX in interfacial stabilization beyond traditional plant-based counterparts.
  • Al2O3 coating grown on Nafion membranes by atomic layer deposition
    (2015-12-01) Toikkanen, Outi; Nisula, Mikko; Pohjalainen, Elina; Hietala, Sami; Havansi, Hannele; Ruotsalainen, Jussi; Halttunen, Sakari; Karppinen, Maarit; Kallio, Tanja
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Nafion membranes were shown to be suitable substrates for atomic layer deposition (ALD) process. ALD utilising trimethyl aluminum as a precursor leads to well reproducible formation of smooth single-sided Al2O3 coating on the membranes. Physicochemical and mechanical properties of the coated membranes were compared to those of the unmodified ones. The coating reduced water uptake and thus also conductivity. Moreover, the Al2O3 coating decreased the oxygen permeability of the membrane by 10 % and the methanol permeability 30-50 %. The mechanical properties of the Nafion® membrane were improved. The resulting membranes were successfully applied in hydrogen fuel cells, direct methanol fuel cells and microbial fuel cells. In the microbial fuel cell, the Al2O3 coated membrane showed stable performance during long-term measurements of more than 100 d and doubled power densities in comparison to a cell equipped with a pristine membrane. The membrane modification strategy has potential for improving the performance of various types of membrane fuel cells and could be used for several types of functional membranes containing active groups for ALD growth.
  • Efficient Isolation Method for Highly Charged Phosphorylated Cellulose Nanocrystals
    (2023-03-13) Kröger, Marcel; Badara, Olamide; Pääkkönen, Timo; Schlapp-Hackl, Inge; Hietala, Sami; Kontturi, Eero
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Phosphorylation of cellulose nanocrystals (CNCs) has remained a marginal activity despite the undisputed application potential in flame-retardant materials, sustainable high-capacity ion-exchange materials, or substrates for biomineralization among others. This is largely due to strenuous extraction methods prone to a combination of poor reproducibility, low degrees of substitution, disappointing yields, and impractical reaction sequences. Here, we demonstrate an improved methodology relying on the modification routines for phosphorylated cellulose nanofibers and hydrolysis by gaseous HCl to isolate CNCs. This allows us to overcome the aforementioned shortcomings and to reliably and reproducibly extract phosphorylated CNCs with exceptionally high surface charge (2000 mmol/kg) in a straightforward routine that minimizes water consumption and maximizes yields. The CNCs were characterized by NMR, ζpotential, conductometric titration, thermogravimetry, elemental analysis, wide-angle X-ray scattering, transmission electron microscopy, and atomic force microscopy.
  • Enhancing Biobutanol Production from biomass willow by pre-removal of water extracts or bark
    (2021-12-10) Dou, Jinze; Chandgude, Vijaya; Vuorinen, Tapani; Bankar, Sandip; Hietala, Sami; Lê, Huy Quang
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Aiming to understand the importance of debarking on the controlled utilization of phenolic-rich willow biomass, biobutanol was produced from it by using Clostridium acetobutylicum. Acid-catalysed steam explosion and enzymatic hydrolysis (EH) were investigated before the acetone-butanol-ethanol (ABE) fermentation. The hydrolysable sugar yield and ABE fermentation efficiency were found to decline progressively from willow wood (WW) to HWE WB (hot water extracted willow biomass), WB (willow biomass) and the WW + HWE (willow wood plus the artificial willow bark water extracts), indicating that the pre-removal of water extracts or the bark can significantly improve ABE yield. Notably, the ABE productivity of WW achieved 12.7 g/L at the solvent yield of 31%, and the butanol concentration (i.e. 8.5 g/L) generated by WW is relatively high among the reported lignocellulosic-derived biomass. Additionally, it is hypothesized that under acidic conditions and high temperatures the fructose present in willow water extracts form hydroxymethylfurfural during steam explosion, which then spontaneously condenses with phenolic substances of willow bark to form a solid furanic precipitate. The formed furanic precipitates play inhibitory role in the enzymatic hydrolysis and are thereby deleterious to the ABE fermentation.
  • Fabrication of hydrogel microspheres via microfluidics using inverse electron demand Diels-Alder click chemistry-based tetrazine-norbornene for drug delivery and cell encapsulation applications
    (2023-06-13) Pareja Tello, Rubén; Wang, Shiqi; Fontana, Flavia; Correia, Alexandra; Molinaro, Giuseppina; López Cerdà, Sandra; Hietala, Sami; Hirvonen, Jouni; Barreto, Goncalo; Santos, Hélder A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Microfluidic on-chip production of polymeric hydrogel microspheres (MPs) can be designed for the loading of different biologically active cargos and living cells. Among different gelation strategies, ionically crosslinked microspheres generally show limited mechanical properties, meanwhile covalently crosslinked microspheres often require the use of crosslinking agents or initiators with limited biocompatibility. Inverse electron demand Diels Alder (iEDDA) click chemistry is a promising covalent crosslinking method with fast kinetics, high chemoselectivity, high efficiency and no cross-reactivity. Herein, in situ gellable iEDDA-crosslinked polymeric hydrogel microspheres are developed via water-in-oil emulsification (W/O) glass microfluidics. The microspheres are composed of two polyethylene glycol precursors modified with either tetrazine or norbornene as functional moieties. Using a single co-flow glass microfluidic platform, homogenous MPs of sizes 200-600 μm are developed and crosslinked within 2 minutes. The rheological properties of iEDDA crosslinked bulk hydrogels are maintained with a low swelling degree and a slow degradation behaviour under physiological conditions. Moreover, a high-protein loading capacity can be achieved, and the encapsulation of mammalian cells is possible. Overall, this work provides the possibility of developing microfluidics-produced iEDDA-crosslinked MPs as a potential drug vehicle and cell encapsulation system in the biomedical field.
  • Identification of a polyfuran network as the initial carbonization intermediate in cellulose pyrolysis: A comparative analysis with cellulosic hydrochars
    (2024-08) Fliri, Lukas; Dubivka, Kseniia; Rusakov, Dmitrii; Volikov, Alexander; Guizani, Chamseddine; Hietala, Sami; Filonenko, Svitlana; Hummel, Michael
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Pyrolysis of cellulose is accompanied with different complex and superimposing transformations resulting in a broad mixture of isolable products with strong variations depending on the applied reaction conditions. The operative chemistry represents a challenge for analytical chemists and process engineers alike. Especially, the reactions leading to char formation cannot be described as sufficiently understood. In ongoing efforts to shed light on the major transformations during charring of cellulose, the occurrence of a thermostable condensed phase (TSCP) previously postulated as an important carbonization intermediate formed below 300 °C was revisited. It was attempted to isolate pure TSCP intermediates without cellulose contamination by applying dehydration catalysts known from cellulose based carbon fiber production and extensive isothermal treatments. It was shown that the weight loss levels off during isothermal treatment for 6 h in the temperature range of 200–250 °C, resulting in the formation of a common intermediate with an almost identical composition – irrespective of the employed temperature or catalyst. Moreover, isothermal treatment of pure cellulose at 270–280 °C for up to 12 hours also resulted in the formation of an intermediate which had a similar composition as the material prepared with added dehydration catalysts. To test the hypothesis of a proposed polyfuranic nature of the TSCP intermediate the prepared samples were compared with hydrochars obtained from hydrothermal treatment of cellulose as reference material for a polyfuranic humin. Similarities and differences are discussed and implications for the overall carbonization mechanism are summarized.
  • Interfacial Polyelectrolyte Complex Spinning of Cellulose Nanofibrils for Advanced Bicomponent Fibers
    (2017-04-10) Toivonen, Matti S.; Kurki-Suonio, Sauli; Wagermaier, Wolfgang; Hynninen, Ville; Hietala, Sami; Ikkala, Olli
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Fiber spinning of anionic TEMPO-oxidized cellulose (TOCN) nanofibrils with polycations by interfacial polyelectrolyte complexation is demonstrated. The formed fibers were mostly composed of cellulose nanofibrils and the polycations were a minor constituent, leading to yield and ultimate strengths of ca. 100 MPa and ca. 200 MPa, and Young’s modulus of ca. 15 GPa. Stretching of the as-formed wet filaments of TOCN/polycation by 20% increased the Young’s modulus, yield strength, and ultimate tensile strength by approximately 45, 36, and 26%, respectively. Importantly, feasibility of compartmentalized wound bicomponent fibers by simultaneous spinning of two fibers of different compositions and entwining them together was shown. This possibility was further exploited to demonstrate reversible shape change of a bicomponent fiber directly by humidity change, and indirectly by temperature changes based on thermally dependent humidity absorption. The demonstrated route for TOCN-based fiber preparation is expected to open up new avenues in the application of nanocelluloses in advanced fibrous materials, crimping, and responsive smart textiles.
  • Inverse Thermoreversible Mechanical Stiffening and Birefringence in a Methylcellulose/Cellulose Nanocrystal Hydrogel
    (2018-07-09) Hynninen, Ville; Hietala, Sami; McKee, Jason R.; Murtomäki, Lasse; Rojas Gaona, Orlando; Ikkala, Olli; Nonappa, Nonappa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We show that composite hydrogels comprising methyl cellulose (MC) and cellulose nanocrystal (CNC) colloidal rods display a reversible and enhanced rheological storage modulus and optical birefringence upon heating, i.e., inverse thermoreversibility. Dynamic rheology, quantitative polarized optical microscopy, isothermal titration calorimetry (ITC), circular dichroism (CD), and scanning and transmission electron microscopy (SEM and TEM) were used for characterization. The concentration of CNCs in aqueous media was varied up to 3.5 wt % (i.e, keeping the concentration below the critical aq concentration) while maintaining the MC aq concentration at 1.0 wt %. At 20 °C, MC/CNC underwent gelation upon passing the CNC concentration of 1.5 wt %. At this point, the storage modulus (G′) reached a plateau, and the birefringence underwent a stepwise increase, thus suggesting a percolative phenomenon. The storage modulus (G′) of the composite gels was an order of magnitude higher at 60 °C compared to that at 20 °C. ITC results suggested that, at 60 °C, the CNC rods were entropically driven to interact with MC chains, which according to recent studies collapse at this temperature into ring-like, colloidal-scale persistent fibrils with hollow cross-sections. Consequently, the tendency of the MC to form more persistent aggregates promotes the interactions between the CNC chiral aggregates towards enhanced storage modulus and birefringence. At room temperature, ITC shows enthalpic binding between CNCs and MC with the latter comprising aqueous, molecularly dispersed polymer chains that lead to looser and less birefringent material. TEM, SEM, and CD indicate CNC chiral fragments within a MC/CNC composite gel. Thus, MC/CNC hybrid networks offer materials with tunable rheological properties and access to liquid crystalline properties at low CNC concentrations.
  • Luminescent Gold Nanocluster-Methylcellulose Composite Optical Fibers with Low Attenuation Coefficient and High Photostability
    (2021-07-08) Hynninen, Ville; Chandra, Sourov; Das, Susobhan; Amini, Mohammad; Dai, Yunyun; Lepikko, Sakari; Mohammadi, Pezhman; Hietala, Sami; Ras, Robin H.A.; Sun, Zhipei; Ikkala, Olli; Nonappa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Because of their lightweight structure, flexibility, and immunity to electromagnetic interference, polymer optical fibers (POFs) are used in numerous short-distance applications. Notably, the incorporation of luminescent nanomaterials in POFs offers optical amplification and sensing for advanced nanophotonics. However, conventional POFs suffer from nonsustainable components and processes. Furthermore, the traditionally used luminescent nanomaterials undergo photobleaching, oxidation, and they can be cytotoxic. Therefore, biopolymer-based optical fibers containing nontoxic luminescent nanomaterials are needed, with efficient and environmentally acceptable extrusion methods. Here, such an approach for fibers wet-spun from aqueous methylcellulose (MC) dispersions under ambient conditions is demonstrated. Further, the addition of either luminescent gold nanoclusters, rod-like cellulose nanocrystals or gold nanocluster-cellulose nanocrystal hybrids into the MC matrix furnishes strong and ductile composite fibers. Using cutback attenuation measurement, it is shown that the resulting fibers can act as short-distance optical fibers with a propagation loss as low as 1.47 dB cm−1. The optical performance is on par with or even better than some of the previously reported biopolymeric optical fibers. The combination of excellent mechanical properties (Young's modulus and maximum strain values up to 8.4 GPa and 52%, respectively), low attenuation coefficient, and high photostability makes the MC-based composite fibers excellent candidates for multifunctional optical fibers and sensors.
  • Methyl cellulose/cellulose nanocrystal nanocomposite fibers with high ductility
    (2019-03-01) Hynninen, Ville; Mohammadi, Pezhman; Wagermaier, Wolfgang; Hietala, Sami; Linder, Markus B.; Ikkala, Olli; Nonappa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Methylcellulose/cellulose nanocrystal (MC/CNC) nanocomposite fibers showing high ductility and high modulus of toughness were prepared by a simple aqueous wet-spinning from corresponding nanocomposite hydrogels into ethanol coagulation bath followed by drying. The hydrogel MC aq. concentration was maintained at 1 wt-% while the CNC aq. loading was systematically varied in the range 0–3 wt-%. This approach resulted in MC/CNC fiber compositions from 25/75 wt-%/wt-% to 95/5 wt-%/wt-%. The optimal mechanical properties were achieved with the MC/CNC composition of 80/20 wt-%/wt-% allowing high strain (36.1%) and modulus of toughness (48.3 MJ/m3), still keeping a high strength (190 MPa). Further, we demonstrate that the continuous spinning of MC/CNC fibers is potentially possible. The results indicate possibilities to spin MC-based highly ductile composite fibers from environmentally benign aqueous solvents.
  • Mild alkaline separation of fiber bundles from eucalyptus bark and their composites with cellulose acetate butyrate
    (2021-07) Dou, Jinze; Karakoç, Alp; Johansson, Leena-Sisko; Hietala, Sami; Evtyugin, Dmitry; Vuorinen, Tapani
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    High surface lignin content (i.e. 34.6 %) sclerenchyma fiber bundles were successfully isolated with a yield of 71 % by a mild alkali (NaOH dosage of 5 wt%) extraction of eucalyptus (Eucalyptus globulus) bark under 100 °C for 60 min. The mechanical properties of the composites prepared by hot pressing of cellulose acetate butyrate (CAB) sheets with the fiber bundles were evaluated. The fiber bundles exhibited good compatibility with CAB due to their hydrophobic fiber surfaces. The mechanical properties of the fiber bundle/ cellulose acetate butyrate composites revealed the maximum at a weight ratio of 25:75, which demonstrates the promise of utilizing these isotropic aligned fiber bundles as the reinforcement to the cellulose acetate butyrate without the addition of plasticizers for composite uses.
  • Plasticized Cellulosic Films by Partial Esterification and Welding in Low-Concentration Ionic Liquid Electrolyte
    (2019-05-13) Niu, Xun; Liu, Yating; King, Alistair W.T.; Hietala, Sami; Pan, Hui; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Alternatives to petroleum-based plastics are of great significance not only from the point of view of their scientific and practical impact but to reduce the environmental footprint. Inspired by the composition and structure of wood's cell walls, we used phenolic acids to endow cellulosic fibers with new properties. The fiber dissolution and homogeneous modification were performed with a recyclable ionic liquid (IL) (tetrabutylammonium acetate ([N 4444 ][OAc]):dimethyl sulfoxide) to attain different levels of reaction activity for three phenolic acids (p-hydroxybenzoic acid, vanillic acid, and syringic acid). The successful autocatalytic Fischer esterification reaction was thoroughly investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis, and nuclear magnetic resonance spectroscopy ( 13 C CP-MAS, diffusion-edited 1 H NMR and multiplicity-edited heteronuclear single quantum coherence). Control of the properties of cellulose in the dispersed state, welding, and IL plasticization were achieved during casting and recrystallization to the cellulose II crystalline allomorph. Films of cellulose carrying grafted acids were characterized with respect to properties relevant to packaging materials. Most notably, despite the low degree of esterification (DS < 0.25), the films displayed a remarkable strength (3.5 GPa), flexibility (strains up to 35%), optical transparency (>90%), and water resistance (WCA ∼90°). Moreover, the measured water vapor barrier was found to be similar to that of poly(lactic acid) composite films. Overall, the results contribute to the development of the next-generation green, renewable, and biodegradable films for packaging applications.
  • Polyelectrolyte stabilized nanodiamond dispersions
    (2019-05-01) Tiainen, Tony; Myllymäki, Teemu T.T.; Hatanpää, Timo; Tenhu, Heikki; Hietala, Sami
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Colloidal stability of negatively charged nanodiamonds (ND) has been realized with the help of double hydrophilic block copolymers poly(ethylene oxide)-block-poly(dimethylaminoethyl methacrylate)-dodecyl (PEO-b-PDMAEMA-C12). The polymers were synthesized through RAFT polymerization of DMAEMA with a PEO macromonomer carrying trithiocarbonate and dodecyl end-groups. The NDs and the polymers were complexed by mixing them in different ratios. In addition to the amount of polymers, the effect of the detailed structure of the polymer was of interest and thus, also polymers with different lengths of the PEO-block were synthesized, as well as a block copolymer without the dodecyl end-group. The composition of the polymer, as well as the complexation conditions were varied to find the route to stable nanoparticles. The optimized complexation method gave colloidally stable ND particles with positively charged PDMAEMA coronas. The colloids were stable at room temperature and also in saline solutions up to 0.154 M NaCl.
  • Self-Standing Lignin-Containing Willow Bark Nanocellulose Films for Oxygen Blocking and UV Shielding
    (2021-03-26) Dou, Jinze; Vuorinen, Tapani; Koivula, Hanna; Forsman, Nina; Sipponen, Mika; Hietala, Sami
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Developing the bio-based barrier material to substitute the petroleum-based one is the trend in functional packaging applications. Utilization of the abundantly underappreciated bark biomass is attractive from the sustainability point of view; however, an upgraded approach is required to maximize the performances of the lignin-containing cellulose nanofibril (LCNF) films from willow bark. Herein, hot water extraction (HWE) and microfluidization were studied for their effect on the yield of LCNF and its film performance after treatment of aqueous p-toluenesulfonic acid. The resultant HWE films were superior to the nontreated ones regarding yield, moisture, and oxygen barrier properties. In particular, the HWE films achieved an oxygen permeability of 3 cm3·μm/m2·kPa·day at 50% relative humidity, which is among the lowest achieved for single bio-based materials and comparable to commercially available synthetic barrier films. The LCNF films attained complete blocking of UV light transmission within the wavelength range of 290-400 nm. Overall, this study shows that HWE pretreatment not only allows the recovery of high-value extracts, but also significantly improves the yield of LCNF and its barrier performances. The biocompatible, lignin-containing, and self-standing hydrophobic nanocellulose films show promise as a barrier layer against UV radiation and oxygen permeation in food packaging and other applications.
  • Size-dependent filling effect of crystalline celluloses in structural engineering of composite oleogels
    (2022-04-15) Bhattarai, Mamata; Penttilä, Paavo; Barba, Luisa; Macias-Rodriguez, Braulio; Hietala, Sami; Mikkonen, Kirsi S.; Valoppi, Fabio
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Oleogels are a class of solid-fat mimetics that contain a large fraction of oil. Most of these materials have low stiffness and poor oil-binding capacity at commercially viable concentrations, which limits their application in the food and cosmetic industries. To improve their mechanical behavior, we exploited the concepts of particulate-filled materials by developing oil-continuous monoglyceride composites reinforced with crystalline cellulose of various sizes. Cellulose was used as the reinforcing filler material due to its strength, biodegradability, and abundance. The composites gradually stiffened and became more brittle with a progressive increase of the cellulose weight fraction as the maximum packing fraction of fillers approached. This was manifested as an increase in the viscoelastic moduli and yield stress, consistent with the size of the filler. Based on differential scanning calorimetry, X-ray diffraction, X-ray scattering analyses, and microscopic analyses, the inert surface of crystalline celluloses provided a solid substrate for the crystallization of monoglycerides, favoring the lamellar stacking of monoglyceride molecules during the composite oleogel formation regardless of the cellulose size. The present study suggests that cellulose is a suitable bio-based filler material to obtain mechanically strong oleogels suitable for high-shear applications e.g., in food and pharmaceutical industries.
  • Solid-state NMR method for the quantification of cellulose and polyester in textile blends
    (2019-03-01) Haslinger, Simone; Hietala, Sami; Hummel, Michael; Maunu, Sirkka Liisa; Sixta, Herbert
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The valorization of cellulose rich textile waste is promoted by the development of a novel solid-state NMR method for the quantification of cellulose and polyester in textile blends. We applied 13C CP-MAS NMR as a tool for the quantification and structural characterization of cellulose in cotton polyester blends. Gaussian functions were used to integrate the spectra obtained from a set of calibration standards in order to calculate a sigmoidal calibration curve. Acid hydrolysis was chosen as a reference method. The results demonstrated that solid-state NMR enables a reliable determination of cellulose and polyester in both preconsumer and postconsumer waste textiles and suggests a possible extension of the concept to blends of man-made cellulose fibers (MMCFs) and polyester.
  • Solution-state nuclear magnetic resonance spectroscopy of crystalline cellulosic materials using a direct dissolution ionic liquid electrolyte
    (2023-07) Fliri, Lukas; Heise, Katja; Koso, Tetyana; Todorov, Aleksandar R.; del Cerro, Daniel Rico; Hietala, Sami; Fiskari, Juha; Kilpeläinen, Ilkka; Hummel, Michael; King, Alistair W.T.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Owing to its high sustainable production capacity, cellulose represents a valuable feedstock for the development of more sustainable alternatives to currently used fossil fuel-based materials. Chemical analysis of cellulose remains challenging, and analytical techniques have not advanced as fast as the development of the proposed materials science applications. Crystalline cellulosic materials are insoluble in most solvents, which restricts direct analytical techniques to lower-resolution solid-state spectroscopy, destructive indirect procedures or to ‘old-school’ derivatization protocols. While investigating their use for biomass valorization, tetralkylphosphonium ionic liquids (ILs) exhibited advantageous properties for direct solution-state nuclear magnetic resonance (NMR) analysis of crystalline cellulose. After screening and optimization, the IL tetra-n-butylphosphonium acetate [P4444][OAc], diluted with dimethyl sulfoxide-d 6, was found to be the most promising partly deuterated solvent system for high-resolution solution-state NMR. The solvent system has been used for the measurement of both 1D and 2D experiments for a wide substrate scope, with excellent spectral quality and signal-to-noise, all with modest collection times. The procedure initially describes the scalable syntheses of an IL, in 24–72 h, of sufficient purity, yielding a stock electrolyte solution. The dissolution of cellulosic materials and preparation of NMR samples is presented, with pretreatment, concentration and dissolution time recommendations for different sample types. Also included is a set of recommended 1D and 2D NMR experiments with parameters optimized for an in-depth structural characterization of cellulosic materials. The time required for full characterization varies between a few hours and several days.
  • Stable glycosylamines at the reducing ends of cellulose nanocrystals
    (2023-08-07) Xia, Jingwen; Koso, Tetyana; Heise, Katja; Fliri, Lukas; Ressouche, Emilie; Majoinen, Johanna; Kostiainen, Mauri A.; Hietala, Sami; Hummel, Michael; Aseyev, Vladimir; Kilpeläinen, Ilkka; King, Alistair W.T.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The reaction of reducing end groups in cellulose nanocrystals with dodecylamine was examined. Using a direct-dissolution solution-state NMR protocol, the regioselective formation of glucosylamines was shown. This provides an elegant approach to sustainably functionalize these bio-based nanomaterials, that may not require further reduction to more stable secondary amines.
  • Strain-Stiffening of Agarose Gels
    (2019-06-18) Bertula, Kia; Martikainen, Lahja; Munne, Pauliina M.; Hietala, Sami; Klefström, Juha; Ikkala, Olli; Nonappa, Nonappa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Strain-stiffening is one of the characteristic properties of biological hydrogels and extracellular matrices, where the stiffness increases upon increased deformation. Whereas strain-stiffening is ubiquitous in protein-based materials, it has been less observed for polysaccharide and synthetic polymer gels. Here we show that agarose, that is, a common linear polysaccharide, forms helical fibrillar bundles upon cooling from aqueous solution. The hydrogels with these semiflexible fibrils show pronounced strain-stiffening. However, to reveal strain-stiffening, suppressing wall slippage turned as untrivial. Upon exploring different sample preparation techniques and rheological architectures, the cross-hatched parallel plate geometries and in situ gelation in the rheometer successfully prevented the slippage and resolved the strain-stiffening behavior. Combining with microscopy, we conclude that strain-stiffening is due to the semiflexible nature of the agarose fibrils and their geometrical connectivity, which is below the central-force isostatic critical connectivity. The biocompatibility and the observed strain-stiffening suggest the potential of agarose hydrogels in biomedical applications.
  • Structural features of lignin-hemicellulose-pectin (LHP) orchestrate a tailored enzyme cocktail for potential applications in bark biorefineries
    (2023-07-21) Dou, Jinze; Wang, Jincheng; Hietala, Sami; Evtuguin, Dmitry V.; Vuorinen, Tapani; Zhao, Jian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Wood bark is a structurally complex by-product of the pulp and paper industry, which focuses primarily on the valorization of structurally more regular wood xylem components. The aim of this study was the elucidation of the less valorised willow wood counterparts (whole bark, inner bark, sclerenchyma bundles, and parenchymatous tissues) by NMR spectroscopic techniques. This allowed a better understanding of the structural features of macromolecular components of bark (i.e. pectin, hemicellulose, and lignin), thus providing a base for a more rational design of the customized biochemical processes prior to chemical processing of bark. This crucial knowledge contributed to the creation of a protocol/decision tool to select tailored enzymes (discarding the slightest substrate binding) for the biological pre-treatment of bark to a state suitable for chemical pulping. Such a protocol/decision-making tool would significantly improve the efficiency of enzyme selection by 60-70% due to the specific catalytic activity of the enzymes involved.