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  • 101. Rueda, L.
    et al.
    Fernandez d'Arlas, B.
    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.
    Corcuera, M. A.
    Mondragon, I.
    Eceiza, A.
    Isocyanate-rich cellulose nanocrystals and their selective insertion in elastomeric polyurethane2011In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 71, no 16, p. 1953-1960Article in journal (Refereed)
    Abstract [en]

    Cellulose nanocrystals (CNC) were successfully obtained and modified with 1,6-hexamethylene diisocyanate (HE)!) by means of in situ polymerization varying the CNC/HDI molar ratio to evaluate the number of anchored chains to the CNC. The modification was examined by elemental analysis, nuclear magnetic resonance ((13)C NMR) and attenuated total reflection Fourier transform infrared spectroscopy (IR-ATR). Nanocomposites containing 1.5 wt% CNC, modified and unmodified, were prepared by solvent casting. Thermal and mechanical properties of the resulting films were evaluated from the viewpoint of polyurethane microphase separated structure, soft and hard domains. CNC were effectively dispersed in the polyurethane matrix and depending on surface chemistry, the nanoreinforcement interacts selectively with matrix nanodomains. This interpretation is supported by differences in thermal and mechanical properties of the nanocomposites and also confirmed by AFM images. Isocyanate rich cellulose nanocrystals interacted with matrix hard phase, promoting physical association with hard segments, enhancing stiffness and dimensional stability versus temperature of the nanocomposite.

  • 102.
    Salajkova, Michaela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Wood Nanocellulose Materials and Effects from Surface Modification of Nanoparticles2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nanocellulose is an interesting natural material thatis gaining interest in the field of materials science, particularly nanocomposites. Depending on the disintegration route, nanocellulose can be isolated either in the form of long and flexible fibres (nanofibrillated cellulose, NFC), or stiff, rod-like crystals (cellulose nanocrystals, CNC). Nanocellulose can be utilized in nanocomposites either as a reinforcement element or as a network matrix due to its ability to form a strong network. In this thesis, nanocellulose based materials are prepared by evaporation of a liquid medium. The key step in this processing route is a good dispersion of the nanoparticles in the selected matrix. Therefore the importance of surface modification in order to ensure favourable nanocellulose dispersion is clarified in avariety of materials systems.

    In Paper I, poly(methyl methacrylate) (PMMA) based fibres prepared by electrospinning were reinforced with nanofibrillated cellulose. Native NFC appeared to show a good compatibility with PMMA matrix in the electrospinning solution and resulting fibres. Furthermore, a new method for mechanical testing of mats with random fibre orientation as well as aligned fibres was developed.

    In Paper II, commingled nanopaper structures with carbon nanotubes (CNTs) were prepared. Several surfactants were used to disperse hydrophobic CNTs in water. A nonylphenol phosphate ester (NPPE) was found to work well for both dispersing CNTs in water and providing compatibility with NFC through electrostatic repulsion between the phosphate ester groups of the surfactant and the carboxylate groups of NFC.

    In Paper III, a new water based route for functionalization of cellulose nanocrystals was developed. In this approach, inspired by organo-modified layered silicates, quaternary ammonium salts were adsorbed. It was demonstrated that different functionalities (alkyl, phenyl, glycidylor diallyl) can be introduced onto the cellulose and the dispersibility in organic solvents was studied. Subsequently, in Paper IV, nanocomposites with poly(vinyl acetate) (PVAc)were prepared. The effect of modification on the degree of dispersion of the CNC within the matrix was studied as well as the strong effects on the properties of the resulting nanocomposites.

    In Paper V, taking advantage of the entangled NFC network and the possibility to tailor the pore size and surface chemistry, lubricant-infused slippery films and coatings based on NFC were prepared for the first time.

  • 103.
    Salajkova, Michaela
    et al.
    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.
    Cervin, Nicholas
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Schülz, Christina
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Stockholm University.
    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.
    Bergström, Lennart
    Stockholm University.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Salazar Alvarez, German
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Stockholm University.
    Super-slippery omniphobic self-standing films and coatings based on nanocelluloseManuscript (preprint) (Other academic)
  • 104.
    Salajkova, Michaela
    et al.
    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.
    Valentini, Luca
    Zhou, Qi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Biotechnology (BIO), Glycoscience. 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.
    Tough nanopaper structures based on cellulose nanofibers and carbon nanotubes2013In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 87, p. 103-110Article in journal (Refereed)
    Abstract [en]

    Carbon nanotube (CNT) nanocomposites based on CNT in a polymer matrix typically have low strain to failure in tensile loading. Furthermore, mixing of more than a few percent of CNT with either molten thermoplastics or monomers in bulk often results in agglomeration of CNT. Here, multiwalled CNT (MWCNT) are mixed with nanofibrillated cellulose (NFC) in aqueous suspension and filtered into tough nanopaper structures with up to 17 wt% of MWCNT commingled with NFC nanofibrils. Carbon nanotubes were surface treated with a surfactant, and homogenous suspensions of carbon nanotubes in water miscible with the NFC suspension was obtained. NFC/CNT nanopaper structures were characterized for porosity using mercury displacement, and studied by FE-SEM and AFM. Mechanical properties were tested in uniaxial tension and electrical conductivity was measured. The processing route is environmentally friendly and leads to well-mixed structures. Thin coatings as well as thicker films can be prepared, which show a combination of high electrical conductivity, flexibility in bending and high tensile strength.

  • 105.
    Salajková, Michaela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Nanocelluloses - surface modification and use in functional materials2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cellulose nanocomposites offer interesting potential in terms of improved properties and new functionalities compared with microcomposites. Preparation from colloidal suspensions is promising, since high reinforcement content is possible and a wide range of constituents can be used. In the first study, the challenge is to form a stable suspension of well-dispersed carbon nanotubes (CNT) and nanofibrillated cellulose (NFC) in water and to prepare commingled high CNT content nanopaper structures by filtration. Various surfactants were used to modify CNT. The NFC was stabilized by charged carboxylate groups. A nonylphenol phosphate ester surfactant, NPPE, worked well for CNT and provided a stable and well-dispersed water suspension of CNT and NFC. Field emission scanning electron microscopy (FE-SEM), porosimetry and atomic force microscopy (AFM) were used to characterize nanopaper structure, and tensile properties were measured as well as surface resistivity. The processing route is water based and it is possible to prepare thin coatings as well as thicker films with a combination of low surface resistivity, flexibility in bending and high strength and toughness in tension.

     As inspired by organo-modified layered silicates, the objective of the second study is to develop an environmentally friendly procedure for the surface modification of cellulose nanocrystals, CNC, using quaternary ammonium salts via adsorption. In order to obtain higher surface charge density on CNC, a new route is developed for preparation of CNC with carboxylic acid groups. Quanternary ammonium cations bearing alkyl, phenyl, glycidyl, and diallyl groups are used to modify CNC to render their surface more hydrophobic. The structure and surface hydrophobicity of unmodified and modified CNC as well as their dispersibility in organic solvent are characterized by AFM, FE-SEM, Fourier-transformed infrared spectroscopy (FT-IR), X-Ray analysis (XDR) and contact angle measurement (CAM). Future work will focus on surface-modified nanocelluloses in composite materials, in order to learn more about surface treatment effects on nanocomposite properties.

  • 106.
    Salajková, Michaela
    et al.
    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.
    Zhou, Qi
    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.
    Hydrophobic cellulose nanocrystals modified with quaternary ammonium salts2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 37, p. 19798-19805Article in journal (Refereed)
    Abstract [en]

    An environmentally friendly procedure in aqueous solution for the surface modification of cellulose nanocrystals (CNCs) using quaternary ammonium salts via adsorption is developed as inspired by organomodified layered silicates. CNCs with a high carboxylate content of 1.5 mmol g(-1) were prepared by a new route, direct hydrochloric acid hydrolysis of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized nanofibrillated cellulose from a softwood pulp, and characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). Four quaternary ammonium cation surfactants bearing long alkyl, phenyl, glycidyl, and diallyl groups were successfully used to modify CNCs carrying carboxylic acid groups as characterized by Fourier transform infrared spectroscopy (FTIR). The modified CNCs can be redispersed and individualized in an organic solvent such as toluene as observed by scanning transmission electron microscopy (STEM). One may envision removing excess surfactant to obtain CNC with a monolayer of surfactant. The toluene suspension of the modified CNCs showed strong birefringence under crossed polars but no further chiral- nematic ordering was observed. The model surface prepared by the CNCs modified with quaternary ammonium salts bearing C18 alkyl chains showed a significant increase in water contact angle (71 degrees) compared to that of unmodified CNCs (12 degrees). This new series of modified CNCs can be dried from solvent and have the potential to form well-dispersed nanocomposites with non-polar polymers.

  • 107.
    Salajková, Michaela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Valentini, Luca
    Zhou, Qi
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Tough and conductive nanopaper structures, based on cellulose nonofibrils an carbon nanotubes, prepared by processing of aqueous suspensionsManuscript (preprint) (Other academic)
  • 108.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Liu, Andong
    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), Fibre and Polymer Technology, Biocomposites.
    Fast Preparation Procedure for Large, Flat Cellulose and Cellulose/Inorganic Nanopaper Structures2010In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 9, p. 2195-2198Article in journal (Refereed)
    Abstract [en]

    Nanostructured materials are difficult to prepare rapidly and as large structures. The present study is thus significant because a rapid preparation procedure for large, flat, smooth, and optically transparent cellulose nanopaper structures is developed using a semiautomatic sheet former. Cellulose/inorganic hybrid nanopaper is also produced. The preparation procedure is compared with other approaches, and the nanopaper structures are tested in uniaxial tensile tests. Optical transparency and high tensile strength are demonstrated in 200 mm diameter nanopaper sheets, indicating well-dispersed nanofibrils. The preparation time is 1 h for a typical nanopaper thickness of 60 pm. In addition, the application of the nanopaper-making strategy to cellulose/inorganic hybrids demonstrates the potential for "green" processing of new types of nanostructured functional materials.

  • 109.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Salajkova, Michaela
    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, Biocomposites. 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.
    Mechanical performance tailoring of tough ultra-high porosity foams prepared from cellulose I nanofiber suspensions2010In: Soft Matter, ISSN 1744-683X, Vol. 6, no 8, p. 1824-1832Article in journal (Refereed)
    Abstract [en]

    Low-density structures of mechanical function in plants, arthropods and other organisms, are often based on high- strength cellulose or chitin nanofibers and show an interesting combination of flexibility and toughness. Here, a series of plant-inspired tough and mechanically very robust cellular biopolymer foams with porosities as high as 99.5% (porosity range 93.1-99.5%) were therefore prepared by solvent-free freeze-drying from cellulose I wood nanofiber water suspensions. A wide range of mechanical properties was obtained by controlling density and nanofiber interaction in the foams, and density property relationships were modeled and compared with those for inorganic aerogels. Inspired by cellulose-xyloglucan (XG) interaction in plant cell walls, XG was added during preparation of the toughest foams. For the cellulose-XG nanocomposite foams in particular, the mechanical properties at comparable densities were superior to those reported in the literature for clay aerogel/cellulose whisker nanocomposites, epoxy/clay aerogels, polymer/clay/nanotube aerogels, and polymer/silica aerogels. The foam structure was characterized by high-resolution field-emission scanning electron microscopy and the specific surface area was measured by nitrogen physisorption. Dynamic mechanical thermal analysis and uniaxial compression tests were performed. The foam was thermally stable up to 275 degrees C where cellulose started to degrade.

  • 110.
    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.

  • 111.
    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.

  • 112.
    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.

  • 113. 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.

  • 114. 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.

  • 115. 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.

  • 116.
    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.

  • 117.
    Svagan, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Bio-inspired cellulose nanocomposites and foams based on starch matrix2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In 2007 the production of expanded polystyrene (EPS) in the world was over 4 million tonnes and is expected to grow at 6 percent per year. With the increased concern about environmental protection, alternative biodegradable materials from renewable resources are of interest. The present doctoral thesis work successfully demonstrates that starch-based foams with mechanical properties similar to EPS can be obtained by reinforcing the cell-walls in the foams with cellulose nanofibers (MFC).

    High cellulose nanofiber content nanocomposites with a highly plasticized (50/50) glycerol-amylopectin starch matrix are successfully prepared by solvent-casting due to the high compatibility between starch and MFC. At 70 wt% MFC, the nanocomposites show a remarkable combination of high tensile strength, modulus and strain to failure, and consequently very high work to fracture. The interesting combination of properties are due to good dispersion of nanofibers, the MFC network, nanofiber and matrix properties and favorable nanofiber-matrix interaction.

    The moisture sorption kinetics (30% RH) in glycerol plasticized and pure amylopectin film reinforced with cellulose nanofibers must be modeled using a moisture concentration-dependent diffusivity in most cases. The presence of cellulose nanofibers has a strong reducing effect on the moisture diffusivity. The decrease in zero-concentration diffusivity with increasing nanofiber content could be due to geometrical impedance, strong starch-MFC molecular interaction and constrained swelling due to the cellulose nanofiber network present.

    Novel biomimetic starch-based nanocomposite foams with MFC contents up to 40 wt% are successfully prepared by freeze-drying. The hierarchically structured nanocomposite foams show significant increase in mechanical properties in compression compared to neat starch foam. Still, better control of the cell structure could further improve the mechanical properties. The effect of cell wall composition, freeze-drying temperature and freezing temperature on the resulting cell structure are therefore investigated. The freeze-drying temperature is critical in order to avoid cell structure collapse. By changing the starch content, the cell size, anisotropy ratio and ratio between open and closed cells can be altered. A decrease in freezing temperature decreases the cell size and increases the anisotropy ratio.

    Finally, mechanical properties obtained in compression for a 30 wt% MFC foam prepared by freeze-drying demonstrates comparable properties (Young's modulus and yield strength) to expanded polystyrene at 50% RH and similar relative density. This is due to the reinforcing cellulose nanofiber network within the cell walls.

  • 118.
    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.

  • 119.
    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.

  • 120.
    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.

  • 121. 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).

  • 122.
    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.

  • 123.
    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.

  • 124.
    Tang, Hu
    et al.
    KTH, School of Biotechnology (BIO), Glycoscience.
    Butchosa, Nuria
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Bulone, Vincent
    KTH, School of Biotechnology (BIO), Glycoscience.
    Zhou, Qi
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Transparent, hazy and strong macroscopic ribbon of oriented cellulose nanofibrils bearing poly(ethylene glycol)Manuscript (preprint) (Other academic)
  • 125.
    Tang, Hu
    et al.
    KTH, School of Biotechnology (BIO), Glycoscience.
    Butchosa, Nuria
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Zhou, Qi
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    A Transparent, Hazy, and Strong Macroscopic Ribbon of Oriented Cellulose Nanofibrils Bearing Poly(ethylene glycol)2015In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 27, no 12, p. 2070-2076Article in journal (Refereed)
    Abstract [en]

    A macroscopic ribbon of oriented cellulose nanofibrils bearing polyethylene glycol is fabricated by stretching the cellulose nanofibrils network structure in the hydrogel state. The covalently grafted polyethylene glycol on the nanofibril surface facilitates the alignment and compartmentalization of individual nanofibrils in the ribbon. The ribbon has ultrahigh tensile strength (576 +/- 54 MPa), modulus (32.3 +/- 5.7 GPa), high transparency, and haze.

  • 126.
    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.

  • 127. 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)
  • 128. 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.

  • 129.
    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.

  • 130. 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.

  • 131.
    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.

  • 132.
    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)
  • 133. 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.

  • 134.
    Yin, Yafang
    et al.
    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.
    Salmen, Lennart
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Effect of Steam Treatment on the Properties of Wood Cell Walls2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 1, p. 194-202Article in journal (Refereed)
    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).

  • 135.
    Zhou, Qi
    et al.
    KTH, School of Biotechnology (BIO), Glycoscience.
    Malm, Erik
    KTH, School of Biotechnology (BIO), Glycoscience.
    Nilsson, Helena
    Larsson, Per Tomas
    Iversen, Tommy
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Bulone, Vincent
    KTH, School of Biotechnology (BIO), Glycoscience.
    Biomimetic design of cellulose-based nanostructured composites using bacterial cultures2009In: Polymer Preprints, ISSN 0032-3934, Vol. 50, no 2, p. 7-8Article in journal (Refereed)
123 101 - 135 of 135
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