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  • 251.
    Stevanic, Jasna S.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Mikkonen, Kirsi S.
    Xu, Chunlin
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Tenkanen, Maija
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Salmén, Lennart
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Wood cell wall mimicking for composite films of spruce nanofibrillated cellulose with spruce galactoglucomannan and arabinoglucuronoxylan2014Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, nr 14, s. 5043-5055Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two hemicelluloses (HCs), galactoglucomannan (GGM) and arabinoglucuronoxylan (AGX), and nanofibrillated cellulose (NFC) were isolated from spruce wood and used for the preparation of composite films containing high amounts of cellulose, i.e. 85 and 80 wt% of NFC, respectively. The films were prepared in two ways: (i) by the pre-sorption of HCs on NFC and (ii) by the mixing of components in the usual way. Pre-sorption was applied in an attempt to mimic the carbohydrate biosynthesis pattern during wood cell wall development, where HCs were deposited on the cellulose fibrils prior to lignification taking place. It was assumed that pre-sorption would result in a better film-forming as well as stronger and denser composite films. The mechanical, thermal, structural, moisture sorption and oxygen barrier characteristics of such composite films were tested in order to examine whether the performance of composite films prepared by pre-sorption was better, when compared to the performance of composite films prepared by mixing. The performance of composite films was also tested with respect to the HCs used. All the films showed quite similar barrier and mechanical properties. In general, stiff, strong and quite ductile films were produced. The moisture sorption of the films was comparably low. The oxygen barrier properties of the films were in the range of commercially used poly ethylene vinyl alcohol films. However, the pre-sorption procedure for the preparation of composite films resulted in no additional improvement in the performance of the films compared to the corresponding composite films that had been prepared using the mixing process. Almost certainly, the applied mixing process led to an optimal mixing of components for the film performance achieved. The GGM contributed to a somewhat better film performance than the AGX did. Indications were observed for stronger interactions between the GGM and NFC than that for the AGX and NFC.

  • 252.
    Svagan, Anna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Azizi Samir, My A. S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Biomimetic Foams of High Mechanical Performance Based on Nanostructured Cell Walls Reinforced by Native Cellulose Nanofibrils2008Inngår i: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 20, nr 7, s. 1263-1269Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     A bioinspired foam in which cellulose nanofibrils are used to reinforce cell walls (ca. 3 mu m) is presented. The nanocomposite foams are prepared by a lyophilization technique and show composite structure at the cell-wall scale. The nanocellulosic network shows remarkable mechanical performance, expressed in much-improved modulus and yield strength compared with the neat starch foam.

  • 253.
    Svagan, Anna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Azizi Samir, My Ahmed Said
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Biomimetic polysaccharide nanocomposites of high cellulose content and high toughness2007Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, nr 8, s. 2556-2563Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plant cell walls combine mechanical stiffness, strength and toughness despite a highly hydrated state. Inspired by this, a nanostructured cellulose network is combined with an almost viscous polysaccharide matrix in the form of a 50/50 amylopectin-glycerol blend. Homogeneous films with a microfibrillated cellulose (MFC) nanofiber content in the range of 10-70 wt % are successfully cast. Characterization is carried out by dynamic mechanical analysis, field-emission scanning electron microscopy, X-ray diffraction, and mercury density measurements. The MFC is well dispersed and predominantly oriented random-in-the-plane. High tensile strength is combined with high modulus and very high work of fracture in the nanocomposite with 70 wt % WC. The reasons for this interesting combination of properties include nanofiber and matrix properties, favorable nanofiber-matrix interaction, good dispersion, and the ability of the MFC network to maintain its integrity to a strain of at least 8%.

  • 254.
    Svagan, Anna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Azizi Samir, My
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Nanocomposite cellulose-starch foams prepared by lyophilizationManuskript (Annet vitenskapelig)
  • 255.
    Svagan, Anna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Jensen, Poul
    A cellulose nanocomposite biopolymer foam competing with expanded polystyrene (EPS): hierarchical structure effects on energy absorptionManuskript (Annet vitenskapelig)
    Abstract [en]

    Starch is an interesting biofoam candidate as replacement of expanded polystyrene (EPS) in packaging materials. The main technical problems with starch foam include its hygroscopic nature, sensitivity of its mechanical properties to moisture content and much lower energy  absorption than EPS. In the present study, a starch-based biofoam is able to reach comparable mechanical properties (Young’s modulus, compression yield strength) to expanded polystyrene at 50% relative humidity. The reason is the cellulose nanocomposite concept in the form of a cellulose nanofiber network reinforcing the hygroscopic amylopectin matrix in the cell wall. The biofoams are prepared by freeze-drying and subjected to compressive loading. Cell structure is characterized by FE-SEM of cross-sections. Mechanical properties are related to cell structure and cell wall nanocomposite composition. Hierarchically structured biofoams are demonstrated to be interesting materials with potential for strongly improved mechanical properties. The present study also highlights the challenges involved in preparation and analysis of nanocomposite foams structured at several different scales.

  • 256.
    Svagan, Anna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Hedenqvist, Mikael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Reduced water vapour sorption in cellulose nanocomposites with starch matrix2009Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 69, nr 3-4, s. 500-506Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of microfibrillated cellulose nanofibers from wood on the moisture sorption kinetics (30% RH) of glycerol plasticized and pure high-amylopectin starch films were studied. The presence of a nanofiber network (70 wt% cellulose nanofibers) reduced the moisture uptake to half the value of the pure plasticized starch film. The swelling yielded a moisture concentration-dependent diffusivity. Quite surprisingly, the moisture diffusivity decreased rapidly with increasing nanofiber content and the diffusivity of the neat cellulose network was, in relative terms, very low. It was possible to describe the strong decrease in zero-concentration diffusivity with increasing cellulose nanofiber/matrix ratio, simply by assuming only geometrical blocking using the model due to Aris. The adjusted model parameters suggested a "simplified" composite structure with dense nanofiber layers oriented in the plane of the film. Still, also constraining effects on swelling from the high modulus/hydrogen bonding cellulose network and reduced amylopectin molecular mobility due to strong starch-cellulose molecular interactions were suggested to contribute to the reductions in moisture diffusivity.

  • 257.
    Svagan, Anna J.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Jensen, Poul
    Cellulose Nanocomposite Biopolymer Foam-Hierarchical Structure Effects on Energy Absorption2011Inngår i: ACS APPLIED MATERIALS & INTERFACES, ISSN 1944-8244, Vol. 3, nr 5, s. 1411-1417Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Starch is an attractive biofoam candidate as replacement of expanded polystyrene (EPS) in packaging materials. The main technical problems with starch foam include its hygroscopic nature, sensitivity of its mechanical properties to moisture content, and much lower energy absorption than EPS. In the present study, a starch-based biofoam is for the first time able to reach comparable mechanical properties (E = 32 MPa, compressive yield strength, 630 kPa) to EPS at 50% relative humidity and similar relative density. The reason is the nanocomposite concept concept in the form of a cellulose nanofiber network reinforcing the hygroscopic amylopectin starch matrix in the cell wall. The biofoams are prepared by the freezing/freeze-drying technique and subjected to compressive loading. Cell structure is characterized by FE-SEM of cross sections. Mechanical properties are related to cell structure and cell wall nanocomposite composition. Hierarchically structured biofoams are demonstrated to be interesting materials with potential for strongly improved mechanical properties.

  • 258. Svagan, Anna J.
    et al.
    Musyanovych, Anna
    Kappl, Michael
    Bernhardt, Max
    Glasser, Gunnar
    Wohnhaas, Christian
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Risbo, Jens
    Landfester, Katharina
    Cellulose Nanofiber/Nanocrystal Reinforced Capsules: A Fast and Facile Approach Toward Assembly of Liquid-Core Capsules with High Mechanical Stability2014Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 15, nr 5, s. 1852-1859Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Liquid-core capsules of high mechanical stability open up for many solid state-like applications where functionality depending on liquid mobility is vital. Herein, a novel concept for fast and facile improvement of the mechanical properties of walls of liquid-core capsules is reported. By imitating nature's own way of enhancing the mechanical properties in liquid-core capsules, the parenchyma plant cells found in fruits and vegetables, a blend of short cellulose nanofibers (<1 mu m, NFC) and nanocrystals (CNC) was exploited in the creation of the capsule walls. The NFC/CNC blend was prepared from a new version of the classical wood pulp hydrolysis. The capsule shell consisted of a covalently (by aromatic diisocyanate) cross-linked NFC/CNC structure at the outer capsule wall and an inner layer dominated by aromatic polyurea. The mechanical properties revealed an effective capsule elastic modulus of 4.8 GPa at 17 wt % NFC/CNC loading, about six times higher compared to a neat aromatic polyurea capsule (0.79 GPa) and 3 orders of magnitude higher than previously reported capsules from regenerated cellulose (0.0074 GPa). The outstanding mechanical properties are ascribed to the dense nanofiber structure, present in the outer part of the capsule wall, that is formed by oriented NFC/CNC of high average aspect ratio (L/d similar to 70) and held together by both covalent (urethane bonds) and physical bonds (hydrogen bonds).

  • 259.
    Svagan, Anna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Jensen, Poul
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Furó, István
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Dvinskikh, Sergey
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Towards tailored hierarchical structures in starch-based cellulose nanocomposite foams prepared by freeze-dryingManuskript (Annet vitenskapelig)
    Abstract [en]

    The properties of nanocomposite foams depend both on cell wall composition and cell structure. In order to fully realize the potential of these materials, both cell wall composition and cell structure must be controlled and tailored. The effect of freezing and freeze-drying temperature on cell structure in nanocomposite foams based on starch and microfibrillated cellulose (MFC) is studied. Freezing experiments are combined with DSC and NMR-analysis of bound water content in order to determine a suitable freeze-drying temperature. The freeze-drying temperature is critical in order to avoid cell structure collapse, as found from cell structure studies by FE-SEM microscopy. Based on this, a foam with mixed open and closed cell structures and as much as 70% MFC in the cell wall was successfully prepared. The study clarifies the interdependence of how the starch-MFC-water suspension composition, in combination with freezing and freeze-drying temperature, will control cell structure of the foams.

  • 260.
    Svagan, Anna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Jensen, Poul
    Natl Museum Denmark.
    Dvinskikh, Sergey
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Furó, István
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Towards tailored hierarchical structures in cellulose nanocomposite biofoams prepared by freezing/freeze-drying2010Inngår i: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 20, nr 32, s. 6646-6654Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cellulose nanofiber (MFC) reinforced starch-based foams, prepared by the freezing/freeze-drying route, are very interesting porous materials due to the strong MFC reinforcement of the cell wall itself. However, in order to fully realize the potential of these nanocomposite biofoams, both cell wall composition and cell structure must be controlled. The effect of starch-MFC-water suspension composition, together with preparation temperature (-27, -78, and -196 degrees C) on the foam cell structure is investigated. NMR-analysis of bound water content, DSC and freezing experiments in combination with freeze-drying experiments and FE-SEM microscopy are used to determine a suitable freeze-drying temperature. The freeze-drying temperature is critical in order to avoid cell structure collapse, as found from FE-SEM studies. By varying the cell-wall composition and preparation temperature, the foam morphology can be manipulated. The connection between cell size and starch content is considered to depend on the inherent properties of starch and a mechanism for ice crystal formation is suggested. Based on improved preparation conditions, foams with mixed open and closed cell structures and as much as 70 wt% MFC in the cell wall are created successfully.

  • 261.
    Terenzi, Camilla
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Prakobna, Kasinee
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Biokompositer. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Furo, Istvan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Nanostructural Effects on Polymer and Water Dynamics in Cellulose Biocomposites: H-2 and C-13 NMR Relaxometry2015Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, nr 5, s. 1506-1515Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Improved moisture stability is desired in cellulose biocomposites. In order to clarify nanostructural effects, a new approach is presented where water and polymer matrix mobilities are characteriied separately. Nanocornposites from cellulose nanofibers (CNF) in the xyloglucan (XG) biopolynier matrix are investigated at different hydration states Films of XG, CNF, and CNF/XG composites are subjected to detailed H-2 and C-13 NMR relaxation studies. Since the H-2 NMR. signal arises from heavy water and the C-13 signal from the polysaccharides, - molecular Water and polymer dynamics is for the first time investigated separately In the neat components, H-2 transverse relaxation (T-2), data are consistent. With water Clustering at the CNF fibril sulfaces, but bulk spread of moisture in XG. The-new method results in a description of water interaction with the nanoscale phases. At low hydration) water molecules at the CNF/XG interface exhibit higher water-mobility-than in neat CNF or XG, due to locally high Water concentration. At the same time, CNF-associated interphase segments of XG Slower NMR-dynamics that in teat XG.

  • 262.
    Terenzi, Camilla
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Prakobna, Kasinee
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Furo, Istvan
    Berglund, Lars
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Interphase effects on polymer and water dynamics in cellulose biocomposites-2H and 13C NMR relaxometry2015Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 250Artikkel i tidsskrift (Annet vitenskapelig)
  • 263. Thuvander, F.
    et al.
    Berglund, Lars A.
    In situ observations of fracture mechanisms for radial cracks in wood2000Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 35, nr 24, s. 6277-6283Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the findings of work carried out to describe the micromechanisms of radial crack growth in wood. TR and TL cracks are both radial cracks but TR grows radially and TL longitudinally. TR cracks are known to show higher fracture toughness than TL cracks. The TR fracture surfaces also indicate a more tortuous crack path. Since the reason for this is unclear, details of the TR crack growth mechanisms in green Pinus sylvestris L were studied. This was done by in-situ optical microscopy as the crack was cutting through alternating layers of soft earlywood and stiff latewood. At the scale of individual cells, the crack tip advanced by separating cell walls at the middle lamella in a splitting or peeling mode. At the scale of growth rings, stick-slip type of crack growth was observed and new crack planes were often formed. The stress distribution in a material with alternating stiff and soft layers is causing this. This stress distribution also contributes to the tendency for inclined cracks to deviate in the radial direction. For interpretation of fracture mechanisms, the importance of scale interaction and the combined influences of microstructure and stress state are emphasized.

  • 264. Thuvander, F.
    et al.
    Kifetew, G.
    Berglund, Lars A.
    Modeling of cell wall drying stresses in wood2002Inngår i: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 36, nr 3, s. 241-254Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    All applications of wood involve drying the material from the green state. The cell wall may be viewed as a laminate consisting of different layers. The layers have different orientations and therefore different moisture expansion characteristics. As a result, stresses will develop in the layers due to drying. Micromechanical models for fibre composite materials were used in combination with a laminate analogy in order to calculate these drying stresses in the cell wall layers S1, S2 and S3. Resulting stresses were very high. In reality viscoelastic effects will significantly reduce stresses at high moisture content. However, at lower moisture content irreversible cell wall damage is likely to form as a result of the stresses computed by the model.

  • 265. Thuvander, F.
    et al.
    Sjodahl, M.
    Berglund, Lars A.
    Measurements of crack tip strain field in wood at the scale of growth rings2000Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 35, nr 24, s. 6267-6275Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fracture mechanisms of wood have often been interpreted on the scale of cell walls. Although this scale is important, the scale of growth rings needs to be considered in the same context. In the present study, the crack tip strain field of radial TR cracks at the scale of growth rings is measured by electronic speckle photography. The methodology is discussed in detail as well as the data reduction scheme. The tip is in the earlywood layer and the crack plane of the TR crack is perpendicular to the stiffer latewood layer. Increasing opening mode load is applied in-situ as the crack is observed by reflected light optical microscopy. Strains are measured on direct images of the microstucture. In contrast to some other methodologies, this allows direct correlation between strain field and microstructure. In the softer earlywood, tangential strains extend considerable distances in the tangential direction. Due to the stiff latewood, the strain is heavily constrained in the radial direction. This nature of the local strain field has been largely neglected, despite its obuius significance to TR crack growth mechanisms.

  • 266. Thuvander, F.
    et al.
    Wallstrom, L.
    Berglund, Lars A.
    Lindberg, K. A. H.
    Effects of an impregnation procedure for prevention of wood cell wall damage due to drying2001Inngår i: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 34, nr 6, s. 473-480Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Drying of wood may lead to readily observable macroscale cracks. Recently observations were made indicating that also at the level of cell walls, damage occurs due to drying. A method is presented where green wood is impregnated using a solution of water and a bulking compound such as glycerol. Tensile strength parallel to the grain for wood impregnated in the green state was compared with that for ordinary dried wood and for wood impregnated after drying. Data demonstrate significantly higher strength for wood impregnated in the green state. It is postulated that this is due to damage in the cell walls of non-impregnated wood where the damage is induced by the drying stresses. Support for this hypothesis is also presented in the form of fractography results. For wood impregnated in the green state, damage development during drying is limited. This is because the impregnating chemical (glycerol in the present case) in the cell wall substitutes some of the moisture and therefore limits the drying stresses.

  • 267.
    Trey, Stacy M.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Netrval, Julia
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Johansson, Mats
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Electron-Beam-Initiated Polymerization of Poly(ethylene glycol)-Based Wood Impregnants2010Inngår i: ACS APPL MATER INTERFACES, ISSN 1944-8244, Vol. 2, nr 11, s. 3352-3362Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The current study demonstrates that methacrylate and acrylate poly(ethylene glycol) (PEG) functional oligomers can be effectively impregnated into wood blocks and cured efficiently to high conversions without catalyst by e-beam radiation, allowing for less susceptibility to leaching, and favorable properties including higher Brinell hardness values. PEG based monomers were chosen because there is a long history of this water-soluble monomer being able to penetrate the cell wall, thus bulking it and decreasing the uptake of water which further protects the wood from fungal attack. Diacrylate dimethacrylate and dihydroxyl functional PEG of M-v, 550-575 of concentration 0-30, 60 and 100 wt % in water, were vacuum pressure impregnated into Scots Pine blocks of 15 x 25 x 50 mm in an effort to bulk the cell wall. The samples were then irradiated and compared with nonirradiated samples it was shown by IR, DSC that the acrylate polymers were fully cured to much higher conversions than can be reached with conventional methods Leaching studies indicated a much lower amount of oligomer loss from the cured to much higher conversions than can be reached with conventional methods functional PEG indication a high degree of fastening of the polymer in the wood. The Brinell hardness indicated a significant increase in hardness to hardwood levels in the modified samples compared to the samples of hydroxyl functional PEG and uncured vinyl PEC samples, which actually became softer than the untreated Scots Pine. By monitoring the dimensions of the sample it was found by weight percent gain calculations WPC %) that water helps to swell the wood structure and allow better access of the oligomers into the cell wall as this was not observed for methyl methacrylate which is well-cocumented to remain in the lumen. However dimensional stability of the viny ploymer modified blocks when placed in water was not observed to the same extent as PEG.

  • 268.
    Trey, Stacy
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Olsson, Richard T.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Johansson, Mats
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Controlled deposition of magnetic particles within the 3-D template of wood: making use of the natural hierarchical structure of wood2014Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, nr 67, s. 35678-35685Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study presents a promising method to make three-dimensional lattices of structured nanomaterials by using wood templates for in situ (confined) directed growth of inorganic material in the ordered cell walls. The wood was impregnated by transition metal ion precursors (iron, manganese and cobalt) at 5 bars pressure that were further transformed into magnetic particles (Fe3O4, MnFe2O4 and CoFe2O4) by addition of alkaline solutions. It was found that by this method, it was possible to produce lightweight ferromagnetic functionalized wood materials in an inexpensive and environmentally friendly way. It was possible to functionalise the wood throughout the structure with a high weight percent of particles from 15-20 wt% as observed by TGA. These were not only adsorbed to the surface of the lumen, but also found by SEM-EDX throughout the cell wall and middle lamella and in higher amounts in early wood. The magnetic properties were nearly unaffected by the incorporation into the wood samples as compared to powder compacts obtained as particles that precipitated separately in the impregnation solution, both for soft and hard magnetic materials. Whereas the hard magnetic phase CoFe2O4 showed insignificant leaching, the soft magnetic Fe3O4, MnFe2O4 lost around 50 wt% during repeated washing in deionized water, suggesting that the CoFe2O4 particles were more readily attached in the structure of the wood. The crystal structure of the magnetic particles was determined to be the same in the wood structure as those formed in solution.

  • 269.
    Vasileva, Elena
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Fotonik.
    Chen, Hui
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Li, Yuanyuan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Sychugov, Ilya
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Yan, Max
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Berglund, Lars
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Popov, Sergei
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Light Scattering by Structurally Anisotropic Media: A Benchmark with Transparent Wood2018Inngår i: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 6, nr 23, artikkel-id 1800999Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transparent wood (TW) is a biocomposite material with hierarchical structure, which exhibits high optical transmittance and anisotropic light scattering. Here, the relation between anisotropic scattering and the internal structure of transparent wood is experimentally studied and the dependence of scattering anisotropy on material thickness, which characterizes the fraction of ballistic photons in the propagating light, is shown. The limitations of the conven-tional haze, as it is implemented to isotropic materials, are discussed, and a modified characteristic parameter of light scattering—the degree of aniso-tropic scattering is defined. This parameter together with the transport mean free path value is more practical and convenient for characterization of the material scattering properties. It is believed that the generic routine described in this paper can be applied for scattering characterization and comparison of other TW materials of either different thickness, optical quality or based on various wood species.

  • 270.
    Vasileva, Elena
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Li, Yuanyuan
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Mensi, Mounir
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Popov, Sergei
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Lasing from Organic Dye Molecules Embedded in Transparent Wood2017Inngår i: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 5, nr 10, artikkel-id 1700057Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The report on a study of laser emission from a conceptually new organic material based on transparent wood (TW) with embedded dye Rhodamine 6G molecules is presented in this paper. The lasing performance is compared to a reference organic material containing dye in a poly-methyl-methacrylate matrix. From experimental results, one can conclude that the optical feedback in dye-TW material is realized within cellulose fibers, which play the role of tiny optical resonators. Therefore, the output emission is a collective contribution of individual resonators. Due to this fact, as well as low Q-factor of the resonators/fibers and their length variation, the spectral line of laser emission is broadened up to several nanometers.

  • 271. Walther, A.
    et al.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Ikkala, O.
    Biomimetic, large-area, layered composites with superior properties2010Inngår i: European Cells and Materials, ISSN 1473-2262, E-ISSN 1473-2262, Vol. 20, nr Suppl.3, s. 267-Artikkel i tidsskrift (Fagfellevurdert)
  • 272. Walther, Andreas
    et al.
    Bjurhager, Ingela
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Malho, Jani-Markus
    Pere, Jaakko
    Ruokolainen, Janne
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Ikkala, Olli
    Large-Area, Lightweight and Thick Biomimetic Composites with Superior Material Properties via Fast, Economic, and Green Pathways2010Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 10, nr 8, s. 2742-2748Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Although remarkable success has been achieved to mimic the mechanically excellent structure of nacre in laboratory-scale models, it remains difficult to foresee mainstream applications due to time-consuming sequential depositions or energy-intensive processes. Here, we introduce a surprisingly simple and rapid methodology for large-area, lightweight, and thick nacre-mimetic films and laminates with superior material properties. Nanoclay sheets with soft polymer coatings are used as ideal building blocks with intrinsic hard/soft character. They are forced to rapidly self-assemble into aligned nacre-mimetic films via paper-making, doctor-Wading or simple painting, giving rise to strong and thick films with tensile modulus of 45 GPa and strength of 250 MPa, that is, partly exceeding nacre. The concepts are environmentally friendly, energy-efficient, and economic and are ready for scale-up via continuous roll-to-roll processes. Excellent gas barrier properties, optical translucency, and extraordinary shape-persistent fire-resistance are demonstrated. We foresee advanced large-scale biomimetic materials, relevant for lightweight sustainable construction and energy-efficient transportation.

  • 273.
    Walther, Andreas
    et al.
    Molecular Materials, Department of Applied Physics, Aalto University.
    Bjurhager, Ingela
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Malho, Jani-Markus
    Molecular Materials, Department of Applied Physics, Aalto University.
    Ruokolainen, Janne
    Molecular Materials, Department of Applied Physics, Aalto University.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Ikkala, Olli
    Molecular Materials, Department of Applied Physics, Aalto University.
    Supramolecular Control of Stiffness and Strength in Lightweight High-Performance Nacre-Mimetic Paper with Fire-Shielding Properties2010Inngår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 49, nr 36, s. 6448-6453Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Taking the heat: Hard/soft core/shell colloidal building blocks allow large-scale self-assembly to form nacre-mimetic paper. The strength and stiffness of this material can be tailored by supramolecular ionic bonds. These lightweight biomimetic materials show excellent and tunable mechanical properties and heat and fire-shielding capabilities.

  • 274. Wang, M.
    et al.
    Olszewska, A.
    Walther, A.
    Malho, J. -M
    Schacher, F. H.
    Ruokolainen, J.
    Ankerfors, M.
    Laine, J.
    Berglund, Lars
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Österberg, M.
    Ikkala, O.
    Colloidal inonic self-assembly between anionic native cellulose nanofibrils and cationic block copolymer micelles into biomimetic nanocomposites2013Inngår i: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2013, s. 6558-6567Konferansepaper (Fagfellevurdert)
  • 275. Wang, Miao
    et al.
    Olszewska, Anna
    Walther, Andreas
    Malho, Jani-Markus
    Schacher, Felix H.
    Ruokolainen, Janne
    Ankerfors, Mikael
    Laine, Janne
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Österberg, Monika
    Ikkala, Olli
    Colloidal Ionic Assembly between Anionic Native Cellulose Nanofibrils and Cationic Block Copolymer Micelles into Biomimetic Nanocomposites2011Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, nr 6, s. 2074-2081Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a facile ionic assembly between fibrillar and spherical colloidal objects toward biomimetic nanocomposites with majority hard and minority soft domains based on anionic reinforcing native cellulose nanofibrils and cationic amphiphilic block copolymer micelles with rubbery core. The concept is based on ionic complexation of carboxymethylated nanofibrillated cellulose (NFC, or also denoted as microfibrillated cellulose, MFC) and micelles formed by aqueous self-assembly of quaternized poly(1,2-butadiene)-block-poly(dimethylaminoethyl methacrylate) with high fraction of the NFC reinforcement. The adsorption of block copolymer micelles onto nanocellulose is shown by quartz crystal microbalance measurements, atomic force microscopy imaging, and fluorescent optical microscopy. The physical properties are elucidated using electron microscopy, thermal analysis, and mechanical testing. The cationic part of the block copolymer serves as a binder to NFC, Whereas the hydrophobic rubbery micellar cores are designed to facilitate energy dissipation and nanoscale lubrication between the NFC domains under deformation. We show that the mechanical properties do not follow the rule of mixtures, and synergistic effects are observed with promoted work of fracture in one composition. As the concept allows wide possibilities for tuning, the work suggests pathways for nanocellulose-based biomimetic nanocomposites combining high toughness with stiffness and strength.

  • 276.
    Wang, Yan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Bergenstråhle-Wohlert, Malin
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Tu, Yaoquan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Wohlert, Jakob
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Swelling and dimensional stability of xyloglucan/montmorillonite nanocomposites in moist conditions from molecular dynamics simulations2017Inngår i: Computational Materials Science, ISSN 0927-0256, Vol. 128, s. 191-197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nacre-mimetic biocomposites made from the combination of montmorillonite clay and the hemicellulose xyloglucan give materials that retain much of their material properties even at high relative humidity. Here, a model composite system consisting of two clay platelets intercalated by xyloglucan oligomers was studied at different levels of hydration using molecular dynamics simulations, and compared to the pure clay. It was found that xyloglucan inhibits swelling of the clay at low water contents by promoting the formation of nano-sized voids that fill with water without affecting the material's dimensions. At higher water contents the XG itself swells, but at the same time maintaining contact with both platelets across the gallery, thereby acting as a physical cross-linker in a manner similar to the role of XG in the plant cell wall.

  • 277.
    Wang, Yan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Wohlert, Jakob
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Bergenstråhle-Wohlert, Malin
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Kochumalayil, Joby J.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Tu, Yaoquan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Molecular Adhesion at Clay Nanocomposite Interfaces Depends on Counterion Hydration-Molecular Dynamics Simulation of Montmorillonite/Xyloglucan2015Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, nr 1, s. 257-265Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nacre-mimetic clay/polymer nanocomposites with clay platelet orientation parallel to the film surface show interesting gas barrier and mechanical properties. In moist conditions, interfacial adhesion is lowered and mechanical properties are reduced. Molecular dynamic simulations (MD) have been performed to investigate the effects of counterions on molecular adhesion at montmorillonite clay (Mnt)-xyloglucan (XG) interfaces. We focus on the role of monovalent cations K+, Na+, and Li+ and the divalent cation Ca2+ for mediating and stabilizing the Mnt/XG complex formation. The conformation of adsorbed XG is strongly influenced by the choice of counterion and so is the simulated work of adhesion. Free energy profiles that are used to estimate molecular adhesion show stronger interaction between XG and clay in the monovalent cation system than in divalent cation system, following a decreasing order of K-Mnt, Na-Mnt, Li-Mnt, and Ca-Mnt. The Mnt clay hydrates differently in the presence of different counterions, leading to a chemical potential of water that is highest in the case of K-Mnt, followed by Na-Mnt and Li-Mnt, and lowest in the case of Ca-Mnt. This means that water is most easily displaced from the interface in the case of K-Mnt, which contributes to the relatively high work of adhesion. In all systems, the penalty of replacing polymer with water at the interface gives a positive contribution to the work of adhesion of between 19 and 35%. Our work confirms the important role of counterions in mediating the adsorption of biopolymer XG to Mnt clays and predicts potassium or sodium as the best choice of counterions for a Mnt-based biocomposite design.

  • 278.
    Wang, Yan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Wohlert, Jakob
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Tu, Yaoquan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Molecular dynamics simulation of strong interaction mechanisms at wet interfaces in clay-polysaccharide nanocomposites2014Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 2, nr 25, s. 9541-9547Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bio-composites comprised of the polysaccharide xyloglucan (XG) and montmorillonite (MTM) clay has potential as a 'green' replacement of conventional petroleum-derived polymers in the packaging industry. These materials have been shown to possess excellent material properties, even in high relative humidity. Although interfacial interaction between XG and MTM, and the molecular structure of XG can be identified as key parameters for the complex formation process and the resulting tensile properties, these properties are usually difficult to address using experimental methods. Here we use molecular dynamics (MD) simulations to study the adsorption of fully atomistic models of both native and chemically modified XG to MTM clay surfaces in explicit water. We show that the driving force for adsorption is a favorable change in enthalpy, and furthermore that native XG adsorbs stronger than modified XG. This highlights the importance of molecular structure details to molecular adhesion. The present study provides insights into the molecular scale adsorption mechanisms and can therefore help in designing routes for further improvements of bio-composite materials.

  • 279.
    Wang, Yan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Wohlert, Jakob
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Zhang, Qiong
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Tu, Yaoquan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Jose, Joby Kochumalayil
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Molecular dynamic simulations of xyloglucan adsorbed onto Na-montmorillonite clay: Exploration of interaction mechanisms and conformational properties2013Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 246, s. 342-POLY-Artikkel i tidsskrift (Annet vitenskapelig)
  • 280.
    Wohlert, Jakob
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Bergenstråhle-Wohlert, Malin
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Deformation of cellulose nanocrystals: entropy, internal energy and temperature dependence2012Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, nr 6, s. 1821-1836Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An in-depth analysis was performed of the molecular deformation mechanisms in cellulose during axial stretching. For the first time, it was demonstrated that entropy affects the stiffness of cellulose nanocrystals significantly. This was achieved through Molecular Dynamics simulations of model nanocrystals subject to constant stress in the axial direction, for nanocrystals of varying lateral dimensions and at different temperatures. The simulations were analyzed in terms of Young's modulus E, which is a measure of the elastic response to applied stress. A weak but significant temperature dependence was shown, with partial derivative E/partial derivative T = -0.05 Gpa K-1 at room temperature, in agreement with experimental numbers. In order to analyze the respective contributions from internal energy and entropy, a decomposition of the total response of the free energy with respect to strain was made. It was shown that the decrease in E with increasing T is due to entropy, and that the magnitude of the decrease is 6-9 % at room temperature compared to the value at 0 K. This was also shown independently by a direct calculation of the vibrational entropy of the cellulose crystal. Finally, it was found that internal hydrogen bonds are contributing to the stiffness by 20 %, mainly by stabilizing the cellulose internal structure.

  • 281.
    Wohlert, Jakob
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    A Coarse-Grained Model for Molecular Dynamics Simulations of Native Cellulose2011Inngår i: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 7, nr 3, s. 753-760Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have constructed a coarse-grained model of crystalline cellulose to be used in molecular dynamics simulations. Using cellobiose from the recently published MARTINI coarse-grained force field for carbohydrates [Lopez, C. A. et al. J. Chem. Theory Comput. 2009, 5, 3195-3210] as a starting point, we have reparameterized the nonbonded interactions to reproduce the partitioning free energies between water and cyclohexane for a series of cellooligomers, cellobiose through cellopentaose. By extrapolating the model to longer cellooligomers, and by assigning special cellulose cellulose nonbonded interactions, we obtain a model which gives a stable, ordered structure in water that closely resembles the crystal structure of cellulose I beta. Furthermore, the resulting model is compatible with an existing coarse-grained force field for proteins. This is demonstrated by a simulation of the motion of the carbohydrate-binding domain of the fungal cellulase Cel7A from Trichoderma reesei on a crystalline cellulose surface. The diffusion coefficient at room temperature is calculated at D-1 = 3.1 x 10(-11) cm(2) s(-1), which is in good agreement with experimental numbers.

  • 282. Wu, Q. J.
    et al.
    Liu, X. H.
    Berglund, Lars A.
    An unusual crystallization behavior in polyamide 6/montmorillonite nanocomposites2001Inngår i: Macromolecular rapid communications, ISSN 1022-1336, E-ISSN 1521-3927, Vol. 22, nr 17, s. 1438-1440Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The crystallization behavior and structure of polyamide 6 (PA6) nanocomposites containing 3 wt.-% montmorillonite (MMT) were investigated for different cooling conditions using differential scanning calorimetry and X-ray diffraction. In sharp contrast to PA6 and other semicrystalline polymers, increased cooling rates resulted in higher crystallinity of PA6/MMT. The. highest crystallinity (60.8%) occurred in the liquid nitrogen-quenched PA6/MMT film. The results show that the gamma -crystalline form is dominant in the rapidly cooled PA6/MMT.

  • 283. Wu, Q. J.
    et al.
    Liu, X. H.
    Berglund, Lars A.
    FT-IR spectroscopic study of hydrogen bonding in PA6/clay nanocomposites2002Inngår i: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 43, nr 8, s. 2445-2449Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fourier transform infrared spectroscopy was used to investigate PA6/clay nanocomposites (PA6CN) with various cooling histories from the melt, including rapid cooling (water-quenched), middle-rate cooling (air-cooling) and slow cooling (mold-cooling). In contrast to pure PA6 dominated by the alpha-phase, the addition of clay silicate layers favor the formation of the gamma-crystalline phase in PA6CN. We focus on the reason why silicate layers favor the formation of gamma-phase in PA6. Vaia et al. suggested that the addition of clay layers forces the amide groups of PA6 out of the plane formed by the chains. This results in conformational changes of the chains, which limits the formation of H-bonded sheets so that the gamma-phase is favored. If this assumption is correct, PA6CN is expected to show some differences as compared with PA6 with respect to hydrogen bonding. The silicate layers were indeed found to weaken the hydrogen bonding both in the alpha- and gamma-phases This was also confirmed by X-ray diffraction studies. The gamma-phase is most likely concentrated in regions close to the silicate layers, whereas the alpha-phase is favored in the bulk matrix.

  • 284.
    Wu, Qiuju
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Henriksson, Marielle
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Liu, Xiaohui
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    A High Strength Nanocomposite Based on Microcrystalline Cellulose and Polyurethane2007Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, nr 12, s. 3687-3692Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A high-strength elastomeric nanocomposite has successfully been prepared by dispersing microcrystalline cellulose in a polyurethane matrix. The resulting nanocomposites show increased strain-to-failure in addition to increased stiffness and strength compared to the unfilled polyurethane. The optimal composite contained 5 wt % cellulose. The average true strength for this composition was 257 MPa, compared with 39 MPa for the neat polyurethane, and showed the highest strain-to-failure. The improvements of stiffness, strength, as well as strain-to-failure are believed to be due to good interaction, by both covalent and hydrogen bonds, between the polyurethane and the cellulose nanofibrils.

  • 285. Yang, Quanling
    et al.
    Saito, Tsuguyuki
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Biokompositer.
    Isogai, Akira
    Cellulose nanofibrils improve the properties of all-cellulose composites by the nano-reinforcement mechanism and nanofibril-induced crystallization2015Inngår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, nr 42, s. 17957-17963Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    All-cellulose nanocomposite films containing crystalline TEMPO-oxidized cellulose nanofibrils (TOCNs) of 0-1 wt% were fabricated by mixing aqueous TOCN dispersions with alkali/urea/cellulose (AUC) solutions at room temperature. The mixtures were cast on glass plates, soaked in an acid solution, and the regenerated gel-like films were washed with water and then dried. The TOCN did not form agglomerates in the composites, and had the structure of TOCN-COOH, forming hydrogen bonds with the hydroxyl groups of the regenerated cellulose molecules. X-ray diffraction analysis revealed that the matrix cellulose molecules increased the cellulose II crystal size upon incorporation of TOCN. As a result, the TOCN/AUC composite films had high Young's modulus, tensile strength, thermal stability and oxygen-barrier properties. The TOCN/AUC composite films are promising all-cellulose nanocomposites for versatile applications as new bio-based materials.

  • 286.
    Yang, Ting
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Long, Hui
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Malkoch, Michael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Gamstedt, E. Kristofer
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hult, Anders
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Characterization of Well-Defined Poly(ethylene glycol) Hydrogels Prepared by Thiol-ene Chemistry2011Inngår i: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 49, nr 18, s. 4044-4054Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Considering the large number of applications for hydrogels, a better understanding of the relation between molecular structure and mechanical properties for well-defined hydrogel is essential. A new library has been compiled of poly(ethylene glycol) polymers (PEG) of different length end functionalized with diallyl, dithiol, and dimethacrylate, and crosslinked with complementary trifunctional crosslinkers. In this study, the hydrogels were initially analyzed by FT-Raman and NMR to study the conversion ratio of the functional groups. The effects of solvent type, solid content concentration, curing time and length of the PEG chains on the final leaching, swelling and tensile properties of the hydrogels were studied.

  • 287.
    Yang, Xuan
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Oriented all-cellulose film based on ramie fiber with high mechanical property and transparency2017Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 253Artikkel i tidsskrift (Annet vitenskapelig)
  • 288.
    Yang, Xuan
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Water-Based Approach to High-Strength All-Cellulose Material with Optical Transparency2018Inngår i: ACS SUSTAINABLE CHEMISTRY & ENGINEERING, ISSN 2168-0485, Vol. 6, nr 1, s. 501-510Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    All-cellulose composites are usually prepared by a partial cellulose dissolution approach, using of ionic liquids or organic solvents. Here, an all-cellulose film based on moist ramie fibers was prepared by hot-pressing. The original ramie fiber was degummed, alkali treated, aligned, and mounted into a specially designed mold. The wet ramie fiber "cake" was pressed into a transparent film. The structure, mechanical properties, moisture sorption, and optical properties of the films were investigated using scanning electron microscopy (SEM), X-ray diffraction, tensile tests, gravimetric method, and integrating sphere devices. The all-cellulose films showed an ultimate strength of 620 MPa and a Young's modulus of 39.7 GPa with low moisture sorption and optical transmittance of 85%. These eco-friendly all-cellulose films are of interest for laminated composites, as coatings and in photonics applications.

  • 289.
    Yang, Xuan
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Berthold, Fredrik
    Berglund, Lars
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    High-Density Molded Cellulose Fibers and Transparent Biocomposites Based on Oriented Holocellulose2019Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, nr 10, s. 10310-10319Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ecofriendly materials based on well-preserved and nanostructured wood cellulose fibers are investigated for the purpose of load-bearing applications, where optical transmittance may be advantageous. Wood fibers are subjected to mild delignification, flow orientation, and hot-pressing to form an oriented material of low porosity. The biopolymer composition of the fibers is determined. Their morphology is studied by scanning electron microscopy, cellulose orientation is quantified by X-ray diffraction, and the effect of beating is investigated. Hot-pressed networks are impregnated by a methyl methacrylate monomer and polymerized to form thermoplastic wood fiber/poly(methyl methacrylate) biocomposites. Tensile tests are performed, as well as optical transmittance measurements. Structure-property relationships are discussed. High-density molded fibers from holocellulose have mechanical properties comparable with nanocellulose materials and are recyclable. The thermoplastic matrix biocomposites showed superior mechanical properties (Young's modulus of 20 GPa and ultimate strength of 310 MPa) at a fiber volume fraction of 52%, with high optical transmittance of 90%. The study presents a scalable approach for strong, stiff, and transparent molded fibers/biocomposites.Ecofriendly materials based on well-preserved and nanostructured wood cellulose fibers are investigated for the purpose of load-bearing applications, where optical transmittance may be advantageous. Wood fibers are subjected to mild delignification, flow orientation, and hot-pressing to form an oriented material of low porosity. The biopolymer composition of the fibers is determined. Their morphology is studied by scanning electron microscopy, cellulose orientation is quantified by X-ray diffraction, and the effect of beating is investigated. Hot-pressed networks are impregnated by a methyl methacrylate monomer and polymerized to form thermoplastic wood fiber/poly(methyl methacrylate) biocomposites. Tensile tests are performed, as well as optical transmittance measurements. Structure-property relationships are discussed. High-density molded fibers from holocellulose have mechanical properties comparable with nanocellulose materials and are recyclable. The thermoplastic matrix biocomposites showed superior mechanical properties (Young's modulus of 20 GPa and ultimate strength of 310 MPa) at a fiber volume fraction of 52%, with high optical transmittance of 90%. The study presents a scalable approach for strong, stiff, and transparent molded fibers/biocomposites.

  • 290.
    Yang, Xuan
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Berthold, Fredrik
    RISE Res Inst Sweden, Master Samuelsgatan 60, SE-11121 Stockholm, Sweden..
    Berglund, Lars
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Preserving Cellulose Structure: Delignified Wood Fibers for Paper Structures of High Strength and Transparency2018Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 19, nr 7, s. 3020-3029Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To expand the use of renewable materials, paper products with superior mechanical and optical properties are needed. Although beating, bleaching, and additives are known to improve industrially produced Kraft pulp papers, properties are limited by the quality of the fibers. While the use of nanocellulose has been shown to significantly increase paper properties, the current cost associated with their production has limited their industrial relevance. Here, using a simple mild peracetic acid (PAA) delignification process on spruce, we produce hemicellulose-rich holocellulose fibers (28.8 wt %) with high intrinsic strength (1200 MPa for fibers with microfibrillar angle smaller than 10 degrees). We show that PAA treatment causes less cellulose/hemicellulose degradation and better preserves cellulose nanostructure in comparison to conventional Kraft pulping. High-density holocellulose papers with superior mechanical properties (Young's modulus of 18 GPa and ultimate strength of 195 MPa) are manufactured using a water-based hot-pressing process, without the use of beating or additives. We propose that the preserved hemicelluloses act as "glue" in the interfiber region, improving both mechanical and optical properties of papers. Holocellulose fibers may be affordable and applicable candidates for making special paper/composites where high mechanical performance and/or optical transmittance are of interest.

  • 291.
    Yin, Yafang
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Berglund, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Salmen, Lennart
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Effect of Steam Treatment on the Properties of Wood Cell Walls2011Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, nr 1, s. 194-202Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Steam treatment is a hygrothermal method of potential industrial significance for improving the dimensional stability and durability of wood materials. The steaming results in different chemical and micromechanical changes in the nanostructured biocomposite that comprise a wood cell wall. In this study, spruce wood (Picea abies Karst.) that had been subjected to high-temperature steaming up to 180 degrees C was examined, using imaging Fourier Transform Infrared (FT-IR) microscopy and nanoindentation to track changes in the chemical structure and the micromechanical properties of the secondary cell wall. Similar changes in the chemical components, due to the steam treatment, were found in earlywood and latewood. A progressive degradation of the carbonyl groups in the glucuronic acid unit of xylan and a loss of mannose units in the glucomannan backbone, that is, a degradation of glucomannan, together with a loss of the C=O group linked to the aromatic skeleton in lignin, was found. The development of the hygroscopic and micromechanical properties that occurred with an elevation in the steam temperature correlated well with this pattern of degradation in the constituents in the biocomposite matrix in the cell wall (hemicellulose and lignin).

  • 292.
    Zhou, Qi
    et al.
    KTH, Skolan för bioteknologi (BIO), Centra, Albanova VinnExcellence Center for Protein Technology, ProNova. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    CHAPTER 9 PLA-nanocellulose Biocomposites2015Inngår i: Poly(lactic acid) Science and Technology: Processing, Properties, Additives and Applications, The Royal Society of Chemistry , 2015Kapittel i bok, del av antologi (Fagfellevurdert)
  • 293.
    Zhou, Qi
    et al.
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Malm, Erik
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Nilsson, Helena
    Larsson, Per Tomas
    Iversen, Tommy
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Bulone, Vincent
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Biomimetic design of cellulose-based nanostructured composites using bacterial cultures2009Inngår i: Polymer Preprints, ISSN 0032-3934, Vol. 50, nr 2, s. 7-8Artikkel i tidsskrift (Fagfellevurdert)
  • 294.
    Zhou, Qi
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Malm, Erik
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Nilsson, Helena
    Larsson, Per Tomas
    Iversen, Tommy
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Bulone, Vincent
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Nanostructured biocomposites based on bacterial cellulosic nanofibers compartmentalized by a soft hydroxyethylcellulose matrix coating2009Inngår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 5, nr 21, s. 4124-4130Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Biomimetic approaches involving environmentally-friendly synthetic pathways provide an opportunity to elaborate novel high-performance biocomposites. Here we have developed a low-energy biosynthetic system for the production of a high-strength composite material consisting of self-assembled and nanostructured cellulosic nanofibers. This biocomposite is analogous to natural composite materials with high strength and hierarchical organization such as wood or tendon. It was generated by growing the bacterium Acetobacter, which naturally produces cellulosic nanofibers, in the presence of hydroxyethylcellulose (HEC). Individual cellulose fibrils were coated by HEC and exhibited a smaller lateral dimension than pure bacterial cellulose (BC) fibrils. They self-assembled to form compartmentalized nanofibers and larger cellulose fibril aggregates compared to pure BC. The tensile strength of nanocomposite films prepared from the compartmentalized cellulosic nanofibers was 20% higher than that of pure BC sheets and wood cellulose nanopapers, and 60% higher than that of conventional BC/HEC blends, while no strain-to-failure decrease was observed. The thin nanoscale coating consisting of hydrated HEC significantly increased the mechanical performance of the nanocomposite films by provoking compartmentalization of individual fibrils.

3456 251 - 294 of 294
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