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  • 251.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Zhou, Qi
    KTH, School of Biotechnology (BIO), Glycoscience.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    High-porosity aerogels of high specific surface area prepared from nanofibrillated cellulose (NFC)2011In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 71, no 13, p. 1593-1599Article in journal (Refereed)
    Abstract [en]

    Low-density aerogels based on nanofibrillated cellulose (NFC) from wood pulp were prepared from NFC aqueous dispersions using solvent exchange from water to tert-butanol followed by tert-butanol freeze-drying. In the present study, the dispersion of NFC nanofibers in the hydrocolloid was very well preserved in the aerogels. The "effective" diameter of the NFC nanofibers in the aerogels is around 10-18 nm corresponding to specific surface areas as high as 153-284 m(2) g(-1). Aerogels based on different NFC nanofibers were studied by FE-SEM, BET analysis (nitrogen gas adsorption), and mechanical properties were measured in compression for different densities of aerogels. The properties are compared with polymer foams and inorganic aerogels. Compared with cellular NFC foams, the present nanofibrous aerogels have lower modulus and show lower stress in compression for a given strain. Tert-butanol freeze-drying can therefore be used to create "soft" aerogels.

  • 252.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Zhou, Qi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Nanofibrillated cellulose for enhancement of strength in high-density paper structures2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 2, p. 182-189Article in journal (Refereed)
    Abstract [en]

    In order to enhance dry and wet strength properties of paper, handsheets were made of wood pulp fibers and nanofibrillated cellulose (NFC). 10% NFC was mixed with wood pulp fibers (90%) subjected to different number of beating revolutions. Effects from xyloglucan (XG) hemicellulose addition were also studied. High density paper handsheets from these mixtures were prepared using a laboratory handsheet former. Strength properties were measured and densities of the materials estimated. Scanning electron microscopy was used to observe paper sheet surfaces. NFC significantly enhances strength for the paper handsheets both at 50% relative humidity and in the wet state so that NFC addition may be an alternative to mechanical beating. The main reason for property improvements is increased density of the final material. Tensile energy absorption improved strongly through favorable fiber-fiber interaction. NFC or NFC/XG addition combined with some mechanical beating may decrease energy needs compared with beating only.

  • 253.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Zhou, Qi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Biotechnology (BIO), Glycoscience.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Nanostructured biocomposites of high toughness-a wood cellulose nanofiber network in ductile hydroxyethylcellulose matrix2011In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 7, no 16, p. 7342-7350Article in journal (Refereed)
    Abstract [en]

    Nanopaper from wood-based nanofibrillated cellulose (NFC) offers vastly improved strength and strain-to-failure compared with plant fiber-based paper and plant fiber biocomposites. In the present study, unique nanostructural toughening effects are reported in cellulose nanofiber/hydroxyethylcellulose (HEC) biocomposites. HEC is an amorphous cellulose derivative of high molar mass and toughness. A previously developed preparation route inspired by paper-making is used. It is "green", scalable, and allows high reinforcement content. In the present concept, nanostructural control of polymer matrix distribution is exercised as the polymer associates with the reinforcement. This results in nanocomposites of a soft HEC matrix surrounding nanofibrillated cellulose forming a laminated structure at the submicron scale, as observed by FE-SEM. We study the effect of NFC volume fraction on tensile properties, thermomechanical stability, creep properties and moisture sorption of the nanocomposites. The results show strong property improvements with NFC content due to the load-carrying ability of the NFC network. At an NFC volume fraction of 45%, the toughness was more than doubled compared with cellulose nanopaper. The present nanocomposite is located in previously unoccupied space in a strength versus strain-to-failure property chart, outside the regions occupied by microscale composites and engineering polymers. The results emphasize the potential for extended composites mechanical property range offered by nanostructured biocomposites based on high volume fraction nanofiber networks.

  • 254.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Zhou, Qi
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Biotechnology (BIO), Glycoscience.
    Ikkala, Olli
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Strong and Tough Cellulose Nanopaper with High Specific Surface Area and Porosity2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 10, p. 3638-3644Article in journal (Refereed)
    Abstract [en]

    In order to better understand nanostructured fiber networks, effects from high specific surface area of nanofibers are important to explore. For cellulose networks, this has so far only been achieved in nonfibrous regenerated cellulose aerogels. Here, nanofibrillated cellulose (NFC) is used to prepare high surface area nanopaper structures, and the mechanical properties are measured in tensile tests. The water in NFC hydrogels is exchanged to liquid CO(2), supercritical CO(2), and tert-butanol, followed by evaporation, supercritical drying, and sublimation, respectively. The porosity range is 40-86%. The nanofiber network structure in nanopaper is characterized by FE-SEM and nitrogen adsorption, and specific surface area is determined. High-porosity TEMPO-oxidized NFC nanopaper (56% porosity) prepared by critical point drying has a specific surface area as high as 48(2) m(2) g(-1). The mechanical properties of this nanopaper structure are better than for many thermoplastics, but at a significantly lower density of only 640 kg m(-3). The modulus is 1.4 GPa, tensile strength 84 MPa, and strain-to-failure 17%. Compared with water-dried nanopaper, the material is softer with substantially different deformation behavior.

  • 255. Shams, Md Iftekhar
    et al.
    Nogi, Masaya
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Yano, Hiroyuki
    The transparent crab: preparation and nanostructural implications for bioinspired optically transparent nanocomposites2012In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 8, no 5, p. 1369-1373Article in journal (Refereed)
    Abstract [en]

    An optically transparent crab-shell with an intact original shape and substantial morphological detail is presented. Inorganic calcium carbonate particles, proteins, lipids and pigments are removed from a native crab-shell, and the remaining chitin nanofibrous structure is impregnated by a monomer and polymerized. The nanostructural implications for man-made nanocomposites are discussed. An important application of the finding is demonstrated as heterogeneous micro-scale crab shell chitin particles are successfully used to process transparent nanocomposites. The incorporation of nanostructured chitin macro-particles not only retains transparency of the matrix resin but also drastically reduces the coefficient of thermal expansion of the polymer. Moreover, the optical transmittance of the composite is stable over a large range of temperatures despite significant inhomogeneity at the mm scale and the large temperature changes in the refractive index of the resin in its isolated state. This class of materials is an interesting candidate for transparent substrates in next-generation electronic devices such as flexible displays and solar cells.

  • 256. Shipsha, Andrey
    et al.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Shear coupling effects on stress and strain distributions in wood subjected to transverse compression2007In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 67, no 08-jul, p. 1362-1369Article in journal (Refereed)
    Abstract [en]

    The mechanical behaviour of a wood board subjected to transverse compression is relevant to the performance of glulam beams and solid wood structures. The wood material can be described as polar orthotropic, due to the annual ring structure and to the differences in moduli in different directions in the radial-tangential plane. Strain measurements are performed on single wood boards using a whole-field digital speckle photography technique. Finite element analysis is performed and compared with experimental data. Good agreement in terms of strain fields and apparent moduli is observed between predictions and data. The experimental data show strong variations in local strain due to the polar orthotropic behaviour of wood in this plane, and the extremely low value for shear modulus G(rt) as compared with the other moduli. This leads to shear coupling effects resulting in large local shear deformation and correspondingly low effective stiffness under transverse global loading.

  • 257. Sjögren, B. A.
    et al.
    Berglund, Lars A.
    The effects of matrix and interface on damage in CRP cross-ply laminates2000In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 60, no 1, p. 9-21Article in journal (Refereed)
    Abstract [en]

    A study has been made of the transverse cracking behavior of a series of cross-ply laminates with different matrices, fiber coatings (sizes) and fiber volume fractions. On the basis of unpublished results, a correlation was assumed between material effects on leakage pressure in pressure vessels of given stacking sequence and transverse cracking behavior in cross-ply laminates. Mechanisms for crack initiation and growth were studied by optical microscopy. The strain ai the onset of transverse cracking, epsilon(TOS), increased and the slope, K. of the curve of crack density as a function of strain decreased as the G(IC) of the matrix increased. Improved fiber/matrix adhesion and lower fiber content had similar effects. The properties of polyester-based composites were usually inferior to those of vinylester composites as a consequence of pre-existing debonds and subcritical cracks resulting from microlevel curing stresses. From observations of failure mechanisms one may infer that proof testing of pipes or pressure vessels will increase the extent of subcritical damage in the material.

  • 258. Soeta, Hiroto
    et al.
    Fujisawa, Shuji
    Saito, Tsuguyuki
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Isogai, Akira
    Low-Birefringent and Highly Tough Nanocellulose-Reinforced Cellulose Triacetate2015In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 20, p. 11041-11046Article in journal (Refereed)
    Abstract [en]

    Improvement of the mechanical and thermal properties of cellulose triacetate (CTA) films is required without sacrificing their optical properties. Here, poly(ethylene glycol) (PEG)-grafted cellulose nanofibril/CTA nanocomposite films were fabricated by casting and drying methods. The cellulose nanofibrils were prepared by 2,2,6,6-tetramethylpiperidine-l-oxyl,(TEMPO)-mediated oxidation, and amine-terminated PEG chains were grafted onto the surfaces of the TEMPO-oxidized cellulose nanofibrils (TOCNs) by ionic bonds. Because of the nanosize effect of TOCNs with a uniform width of similar to 3 nm, the PEG-TOCN/CTA nanocomposite films had high transparency and low bitefringence. The grafted PEG chains enhanced the filler-matrix interactions and crystallization of matrix CTA molecules, resulting in the Young's modulus and toughness of CTA film being significantly improved by PEG-grafted TOCN addition. The coefficient of thermal expansion of the original CTA film was mostly preserved even with the addition of PEG-grafted TOCNs. These results suggest that PEG-TOCNs are applicable to the reinforcement for transparent optical films.

  • 259.
    Soeta, Hiroto
    et al.
    Univ Tokyo, Dept Biomat Sci, Grad Sch Agr & Life Sci, Tokyo 1138657, Japan..
    Lo Re, Giada
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Masuda, Akihiro
    Toray Res Ctr Ltd, Morphol Res Labs, Morphol Res Lab 3, Otsu, Shiga 5208567, Japan..
    Fujisawa, Shuji
    Univ Tokyo, Dept Biomat Sci, Grad Sch Agr & Life Sci, Tokyo 1138657, Japan..
    Saito, Tsuguyuki
    Univ Tokyo, Dept Biomat Sci, Grad Sch Agr & Life Sci, Tokyo 1138657, Japan..
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Isogai, Akira
    Univ Tokyo, Dept Biomat Sci, Grad Sch Agr & Life Sci, Tokyo 1138657, Japan..
    Tailoring Nanocellulose-Cellulose Triacetate Interfaces by Varying the Surface Grafting Density of Poly(ethylene glycol)2018In: ACS OMEGA, ISSN 2470-1343, Vol. 3, no 9, p. 11883-11889Article in journal (Refereed)
    Abstract [en]

    Careful design of the structures of interfaces between nanofillers and polymer matrices can significantly improve the mechanical and'thermal' properties of the overall nanocomposites. Here, we investigate]how the grafting density on the surface of nanocelluloses influences the properties of nanocellulose/cellulose triacetate (CTA) composites. 2,2,6,6 The surface of nanocellulose, which was preparedby tetramethylpiperidine-l-oxyl oxidation, was modified with long poly(ethylene glycol) (PEG) chains at different grafting_ densities. The PEG -grafted nanocelluloses were h omogene ously embedded in CTA matrices. The mechanical and thermal properties of the nanocomposites were characterized. Increasing the grafting density caused the soft PEG chains to form denser and thicker layers around the rigid nanocelluloses. The PEG layers were not completely miscible with the CTA matrix. This structure consfderably enhanced the energy dissipation by allowing sliding at the interface, which increased the toughness of the nanocomposites. The thermal and mechanical properties of the composites could be tailored by controlling the grafting density. These findings provide a deeper understanding about interfacial design for nanocellulose-based composite materials.

  • 260.
    Soeta, Hiroto
    et al.
    Univ Tokyo, Tokyo, Japan..
    Saito, Tsuguyuki
    Univ Tokyo, Dept Biomat Sci, Tokyo, Japan..
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Isogati, Akira
    Univ Tokyo, Tokyo, Japan..
    Grafting density design of surface-modified nanocellulose for polymer composites2018In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 255Article in journal (Other academic)
  • 261. Stepan, Agnes M.
    et al.
    Ansari, Farhan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Gatenholm, Paul
    Nanofibrillated cellulose reinforced acetylated arabinoxylan films2014In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 98, p. 72-78Article in journal (Refereed)
    Abstract [en]

    In this study, acetylated rye arabinoxylan (AcAX) films were reinforced with nanofibrillated cellulose from spruce (NFC) ranging from I to 10 wt% of the total composition. Free-standing composite films were casted without the use of any plasticizers. The homogeneous dispersion of NFC in the films was confirmed with scanning electron microscopy. The ultimate strength and the Young's modulus determined by tensile tests increased from 65 MPa and 2190 MPa for neat AcAX films to 93 MPa and 3360 MPa for the 10% composite films, respectively. The elongation to break of the 10% NFC composite film was a remarkable 10.5%. The moisture absorbed was still less than 8 wt% for the films with 10% NFC content at 97% relative humidity at room temperature, which is low for hemicellulose-based films. The addition of NFC decreased the water permeability of the films at low NFC contents, which was studied in diffusion cells using radioactive labeled water. Thus NFC can be used in an unmodified form as reinforcement in AcAX films to prepare films or coatings that are more water and humidity resistant than neat hemicellulose-based films.

  • 262.
    Stevanic, Jasna S.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Bergström, Elina Mabasa
    Gatenholm, Paul
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Salmén, Lennart
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Arabinoxylan/nanofibrillated cellulose composite films2012In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 47, no 18, p. 6724-6732Article in journal (Refereed)
    Abstract [en]

    There is an increasing interest in substituting petroleum based polymer films, for food packaging applications, with films based on renewable resources. In many of these applications, low oxygen permeability and low moisture uptake of films are required, as well as high enough strength and flexibility. For this purpose, rye arabinoxylan films reinforced with nanofibrillated cellulose was prepared and evaluated. A thorough mixing of the components resulted in uniform films. Mechanical, thermal, structural, moisture sorption and oxygen barrier characteristics of such films are reported here. Reinforcement of arabinoxylan with nanofibrillated cellulose affected the properties of the films positively. A decrease in moisture sorption of the films, as well as an increase in stiffness, strength and flexibility of the films were shown. From these results and dynamic FTIR spectra, a strong coupling between reinforcing cellulose and arabinoxylan matrix was concluded. Oxygen barrier properties were equal or better as compared to the neat rye arabinoxylan film. In general, the high nanofibrillated cellulose containing composite film, i.e. 75 % NFC, showed the best properties.

  • 263.
    Stevanic, Jasna S.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Mikkonen, Kirsi S.
    Xu, Chunlin
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Tenkanen, Maija
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Salmén, Lennart
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Wood cell wall mimicking for composite films of spruce nanofibrillated cellulose with spruce galactoglucomannan and arabinoglucuronoxylan2014In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, no 14, p. 5043-5055Article in journal (Refereed)
    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.

  • 264.
    Svagan, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Azizi Samir, My A. S.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Biomimetic Foams of High Mechanical Performance Based on Nanostructured Cell Walls Reinforced by Native Cellulose Nanofibrils2008In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 20, no 7, p. 1263-1269Article in journal (Refereed)
    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.

  • 265.
    Svagan, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Azizi Samir, My Ahmed Said
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Biomimetic polysaccharide nanocomposites of high cellulose content and high toughness2007In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, no 8, p. 2556-2563Article in journal (Refereed)
    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%.

  • 266.
    Svagan, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Azizi Samir, My
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Nanocomposite cellulose-starch foams prepared by lyophilizationManuscript (Other academic)
  • 267.
    Svagan, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Jensen, Poul
    A cellulose nanocomposite biopolymer foam competing with expanded polystyrene (EPS): hierarchical structure effects on energy absorptionManuscript (Other academic)
    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.

  • 268.
    Svagan, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Hedenqvist, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Reduced water vapour sorption in cellulose nanocomposites with starch matrix2009In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 69, no 3-4, p. 500-506Article in journal (Refereed)
    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.

  • 269.
    Svagan, Anna J.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Jensen, Poul
    Cellulose Nanocomposite Biopolymer Foam-Hierarchical Structure Effects on Energy Absorption2011In: ACS APPLIED MATERIALS & INTERFACES, ISSN 1944-8244, Vol. 3, no 5, p. 1411-1417Article in journal (Refereed)
    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.

  • 270. Svagan, Anna J.
    et al.
    Musyanovych, Anna
    Kappl, Michael
    Bernhardt, Max
    Glasser, Gunnar
    Wohnhaas, Christian
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, 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 Stability2014In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 15, no 5, p. 1852-1859Article in journal (Refereed)
    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).

  • 271.
    Svagan, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Jensen, Poul
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Dvinskikh, Sergey
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Towards tailored hierarchical structures in starch-based cellulose nanocomposite foams prepared by freeze-dryingManuscript (Other academic)
    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.

  • 272.
    Svagan, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Jensen, Poul
    Natl Museum Denmark.
    Dvinskikh, Sergey
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Towards tailored hierarchical structures in cellulose nanocomposite biofoams prepared by freezing/freeze-drying2010In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 20, no 32, p. 6646-6654Article in journal (Refereed)
    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.

  • 273.
    Terenzi, Camilla
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Prakobna, Kasinee
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Nanostructural Effects on Polymer and Water Dynamics in Cellulose Biocomposites: H-2 and C-13 NMR Relaxometry2015In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 5, p. 1506-1515Article in journal (Refereed)
    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.

  • 274.
    Terenzi, Camilla
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Prakobna, Kasinee
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Furo, Istvan
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Interphase effects on polymer and water dynamics in cellulose biocomposites-2H and 13C NMR relaxometry2015In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 250Article in journal (Other academic)
  • 275. Thuvander, F.
    et al.
    Berglund, Lars A.
    In situ observations of fracture mechanisms for radial cracks in wood2000In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 35, no 24, p. 6277-6283Article in journal (Refereed)
    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.

  • 276. Thuvander, F.
    et al.
    Kifetew, G.
    Berglund, Lars A.
    Modeling of cell wall drying stresses in wood2002In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 36, no 3, p. 241-254Article in journal (Refereed)
    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.

  • 277. Thuvander, F.
    et al.
    Sjodahl, M.
    Berglund, Lars A.
    Measurements of crack tip strain field in wood at the scale of growth rings2000In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 35, no 24, p. 6267-6275Article in journal (Refereed)
    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.

  • 278. 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 drying2001In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 34, no 6, p. 473-480Article in journal (Refereed)
    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.

  • 279.
    Trey, Stacy M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Netrval, Julia
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Johansson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Electron-Beam-Initiated Polymerization of Poly(ethylene glycol)-Based Wood Impregnants2010In: ACS APPL MATER INTERFACES, ISSN 1944-8244, Vol. 2, no 11, p. 3352-3362Article in journal (Refereed)
    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.

  • 280.
    Trey, Stacy
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Olsson, Richard T.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Johansson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Controlled deposition of magnetic particles within the 3-D template of wood: making use of the natural hierarchical structure of wood2014In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, no 67, p. 35678-35685Article in journal (Refereed)
    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.

  • 281.
    Vasileva, Elena
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Baitenov, Adil
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Chen, Hui
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Li, Yuanyuan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Yan, Min
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Effect of transparent wood on the polarization degree of light2019In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 44, no 12, p. 2962-2965Article in journal (Refereed)
    Abstract [en]

    We report on the study of polarization properties of light propagating through transparent wood (TW), which is an anisotropically scattering medium, and consider two cases: completely polarized and totally unpolarized light. It was demonstrated that scattered light distribution is affected by the polarization state of incident light. Scattering is the most efficient for light polarized parallel to cellulose fibers. Furthermore, unpolarized light becomes partially polarized (with a polarization degree of 50%) after propagating through the TW. In the case of totally polarized incident light, however, the degree of polarization of transmitted light is decreased, in an extreme case to a few percent, and reveals an unusual angular dependence on the material orientation. The internal hierarchical complex structure of the material, in particular cellulose fibrils organized in lamellae, is believed to be responsible for the change of the light polarization degree. It was demonstrated that the depolarization properties are determined by the angle between the polarization of light and the wood fibers, emphasizing the impact of their internal structure, unique for different wood species.

  • 282.
    Vasileva, Elena
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Chen, Hui
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Li, Yuanyuan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Yan, Max
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Light Scattering by Structurally Anisotropic Media: A Benchmark with Transparent Wood2018In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 6, no 23, article id 1800999Article in journal (Refereed)
    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.

  • 283.
    Vasileva, Elena
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Li, Yuanyuan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Mensi, Mounir
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Lasing from Organic Dye Molecules Embedded in Transparent Wood2017In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 5, no 10, article id 1700057Article in journal (Refereed)
    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.

  • 284. Walther, A.
    et al.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Ikkala, O.
    Biomimetic, large-area, layered composites with superior properties2010In: European Cells and Materials, ISSN 1473-2262, E-ISSN 1473-2262, Vol. 20, no Suppl.3, p. 267-Article in journal (Refereed)
  • 285. Walther, Andreas
    et al.
    Bjurhager, Ingela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Malho, Jani-Markus
    Pere, Jaakko
    Ruokolainen, Janne
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Ikkala, Olli
    Large-Area, Lightweight and Thick Biomimetic Composites with Superior Material Properties via Fast, Economic, and Green Pathways2010In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 10, no 8, p. 2742-2748Article in journal (Refereed)
    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.

  • 286.
    Walther, Andreas
    et al.
    Molecular Materials, Department of Applied Physics, Aalto University.
    Bjurhager, Ingela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    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, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    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 Properties2010In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 49, no 36, p. 6448-6453Article in journal (Refereed)
    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.

  • 287. Wang, M.
    et al.
    Olszewska, A.
    Walther, A.
    Malho, J. -M
    Schacher, F. H.
    Ruokolainen, J.
    Ankerfors, M.
    Laine, J.
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Österberg, M.
    Ikkala, O.
    Colloidal inonic self-assembly between anionic native cellulose nanofibrils and cationic block copolymer micelles into biomimetic nanocomposites2013In: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2013, p. 6558-6567Conference paper (Refereed)
  • 288. Wang, Miao
    et al.
    Olszewska, Anna
    Walther, Andreas
    Malho, Jani-Markus
    Schacher, Felix H.
    Ruokolainen, Janne
    Ankerfors, Mikael
    Laine, Janne
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Österberg, Monika
    Ikkala, Olli
    Colloidal Ionic Assembly between Anionic Native Cellulose Nanofibrils and Cationic Block Copolymer Micelles into Biomimetic Nanocomposites2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 6, p. 2074-2081Article in journal (Refereed)
    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.

  • 289.
    Wang, Yan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Bergenstråhle-Wohlert, Malin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Wohlert, Jakob
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Swelling and dimensional stability of xyloglucan/montmorillonite nanocomposites in moist conditions from molecular dynamics simulations2017In: Computational Materials Science, ISSN 0927-0256, Vol. 128, p. 191-197Article in journal (Refereed)
    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.

  • 290.
    Wang, Yan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wohlert, Jakob
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Bergenstråhle-Wohlert, Malin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Kochumalayil, Joby J.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Molecular Adhesion at Clay Nanocomposite Interfaces Depends on Counterion Hydration-Molecular Dynamics Simulation of Montmorillonite/Xyloglucan2015In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 1, p. 257-265Article in journal (Refereed)
    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.

  • 291.
    Wang, Yan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wohlert, Jakob
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Molecular dynamics simulation of strong interaction mechanisms at wet interfaces in clay-polysaccharide nanocomposites2014In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 2, no 25, p. 9541-9547Article in journal (Refereed)
    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.

  • 292.
    Wang, Yan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wohlert, Jakob
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Zhang, Qiong
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Jose, Joby Kochumalayil
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Molecular dynamic simulations of xyloglucan adsorbed onto Na-montmorillonite clay: Exploration of interaction mechanisms and conformational properties2013In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 246, p. 342-POLY-Article in journal (Other academic)
  • 293.
    Wohlert, Jakob
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Bergenstråhle-Wohlert, Malin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Deformation of cellulose nanocrystals: entropy, internal energy and temperature dependence2012In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, no 6, p. 1821-1836Article in journal (Refereed)
    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.

  • 294.
    Wohlert, Jakob
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    A Coarse-Grained Model for Molecular Dynamics Simulations of Native Cellulose2011In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 7, no 3, p. 753-760Article in journal (Refereed)
    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.

  • 295. Wu, Q. J.
    et al.
    Liu, X. H.
    Berglund, Lars A.
    An unusual crystallization behavior in polyamide 6/montmorillonite nanocomposites2001In: Macromolecular rapid communications, ISSN 1022-1336, E-ISSN 1521-3927, Vol. 22, no 17, p. 1438-1440Article in journal (Refereed)
    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.

  • 296. Wu, Q. J.
    et al.
    Liu, X. H.
    Berglund, Lars A.
    FT-IR spectroscopic study of hydrogen bonding in PA6/clay nanocomposites2002In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 43, no 8, p. 2445-2449Article in journal (Refereed)
    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.

  • 297.
    Wu, Qiuju
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Henriksson, Marielle
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Liu, Xiaohui
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    A High Strength Nanocomposite Based on Microcrystalline Cellulose and Polyurethane2007In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, no 12, p. 3687-3692Article in journal (Refereed)
    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.

  • 298. Yang, Quanling
    et al.
    Saito, Tsuguyuki
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Isogai, Akira
    Cellulose nanofibrils improve the properties of all-cellulose composites by the nano-reinforcement mechanism and nanofibril-induced crystallization2015In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, no 42, p. 17957-17963Article in journal (Refereed)
    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.

  • 299.
    Yang, Ting
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Long, Hui
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Malkoch, Michael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Gamstedt, E. Kristofer
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hult, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Characterization of Well-Defined Poly(ethylene glycol) Hydrogels Prepared by Thiol-ene Chemistry2011In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 49, no 18, p. 4044-4054Article in journal (Refereed)
    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.

  • 300.
    Yang, Xuan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Oriented all-cellulose film based on ramie fiber with high mechanical property and transparency2017In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 253Article in journal (Other academic)
34567 251 - 300 of 309
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