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  • 1.
    Andersson, Richard L.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Mallon, Peter E.
    Salajkova, Michaela
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Hedenqvist, Mikael S.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Olsson, Richard T.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Micromechanics of toughness improved electrospun PMMA fibers with embedded cellulose as tested under in-situ microscopyManuscript (preprint) (Other academic)
  • 2.
    Andersson, Richard L.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Salajkova, Michaela
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Mallon, P. E.
    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.
    Hedenqvist, Mikael S.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Olsson, Richard T.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Micromechanical Tensile Testing of Cellulose-Reinforced Electrospun Fibers Using a Template Transfer Method (TTM)2012In: Journal of polymers and the environment, ISSN 1064-7546, E-ISSN 1572-8900, Vol. 20, no 4, p. 967-975Article in journal (Refereed)
    Abstract [en]

    A template transfer method (TTM) and a fiber fixation technique were established for fiber handling and micro tensile stage mounting of aligned and non-aligned electrospun fiber mats. The custom-made template had been precut to be mounted on a variety of collectors, including a rapidly rotating collector used to align the fibers. The method eliminated need for direct physical interaction with the fiber mats before or during the tensile testing since the fiber mats were never directly clamped or removed from the original substrate. By using the TTM it was possible to measure the tensile properties of aligned poly(methyl methacrylate) (PMMA) fiber mats, which showed a 250 % increase in strength and 450 % increase in modulus as compared to a non-aligned system. The method was further evaluated for aligned PMMA fibers reinforced with cellulose (4 wt%) prepared as enzymatically derived nanofibrillated cellulose (NFC). These fibers showed an additional increase of 30 % in both tensile strength and modulus, resulting in a toughness increase of 25 %. The fracture interfaces of the PMMA-NFC fibers showed a low amount of NFC pull-outs, indicating favorable phase compatibility. The presented fiber handling technique is universal and may be applied where conservative estimates of mechanical properties need to be assessed for very thin fibers.

  • 3.
    Ansari, Farhan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Salajkova, Michaela
    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
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Cellulose nanocomposites - Controlling dispersion and material properties through nanocellulose surface modification2015In: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2015Conference paper (Refereed)
    Abstract [en]

    The use of cellulosic nanofibers as reinforcement in polymer composites offers great advantages over their petroleum counterparts. Apart from being strong, stiff and low density; they are obtained from naturally occurring resources and as such are favorable from an environmental point of view. A major problem while studying nanomaterials is their tendency to agglomerate, thus leading to inhomogeneous distribution within the polymer matrix. This often results in stress concentrations in the matrix rich regions when the material is subjected to load and therefore, limits the potential application of these materials. A common approach to circumvent this is by surface modification, which facilitates the dispersion in non-polar matrices. An environmental friendly approach, inspired by clay chemistry, was used to functionalize the CNC surface. It was shown that the CNC could be modified in a rather convenient way to attach a variety of functional groups on the surface. Primarily, the problem of cellulose nanocrystal (CNC) distribution in a hydrophobic polymer matrix is investigated. Composites prepared from modified CNC were studied and compared with unmodified CNC. The distribution of the CNC is carefully monitored at different stages via UV-Vis spectroscopy and scanning electron microscopy (SEM). The mechanical properties of the resulting materials were characterized by dynamic mechanical as well as uniaxial tensile tests. It was shown that a homogeneous distribution of the CNC exposes a tremendous amount of surface area to interact with the matrix. In such a case, the stress transfer is much more efficient and perhaps, the matrix behavior is modified, which leads to significant improvements in the mechanical properties.

  • 4.
    Ansari, Farhan
    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.
    Salajkova, Michaela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Zhou, Qi
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Lars, Berglund
    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.
    Strong surface treatment effects on reinforcement efficiency in biocomposites based on cellulose nanocrystals in poly(vinyl acetate) matrix2015In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 12, p. 3916-3924Article in journal (Refereed)
    Abstract [en]

    In this work, the problem to disperse cellulose nanocrystals (CNC) in hydrophobic polymer matrices has been addressed through application of an environmentally friendly chemical modification approach inspired by clay chemistry. The objective is to compare the effects of unmodified CNC and modified CNC (modCNC) reinforcement, where degree of CNC dispersion is of interest. Hydrophobic functionalization made it possible to disperse wood-based modCNC in organic solvent and cast well-dispersed nanocomposite films of poly(vinyl acetate) (PVAc) with 1-20 wt % CNC. Composite films were studied by infrared spectroscopy (FT-IR), UV-vis spectroscopy, dynamic mechanical thermal analysis (DMTA), tensile testing, and field-emission scanning electron microscopy (FE-SEM). Strongly increased mechanical properties were observed for modCNC nanocomposites. The reinforcement efficiency was much lower in unmodified CNC composites, and specific mechanisms causing the differences are discussed.

  • 5.
    Cranston, Emily D.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Eita, Mohamed
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Johansson, Erik
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Netrval, Julia
    Salajkova, Michaela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Arwin, Hans
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Determination of Young's Modulus for Nanofibrillated Cellulose Multilayer Thin Films Using Buckling Mechanics2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 4, p. 961-969Article in journal (Refereed)
    Abstract [en]

    The Young's modulus of multilayer films containing nanofibrillated cellulose (NFC) and polyethyleneimine (PEI) was determined Using the strain-induced elastic buckling instability for mechanical measurements (SLEBIMM) technique.(1) Multilayer films were built up on polydimethylsiloxane substrates using electrostatic layer-by-layer assembly. At 50% relative humidity, SIEBIMM gave a constant Young's modulus of 1.5 +/- 0.2 GPa for 35-75 run thick films. Conversely, in vacuum, the Young's modulus was 10 times larger, at 17.2 +/- 1.2 GPa. A slight decrease in buckling wavelength with increasing strain was observed by scanning electron microscopy with in situ compression, and above 10% strain, extensive cracking parallel to the compressive direction occurred. We conclude that whereas PEI acts as a "glue" to hold multiple layers of NFC together, it prevents full development of hydrogen bonding and specific fibril-fibril interactions, and at high humidity, its hygroscopic nature decreases the elastic modulus when compared with pure NFC films.

  • 6.
    Galland, Sylvain
    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.
    Andersson, Richard
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Salajkova, Michaela
    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.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Olsson, Richard
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. 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.
    Cellulose nanofibers decorated with magnetic nanoparticles: synthesis, structure and use in magnetized high toughness membranes for a prototype loudspeaker2013In: Journal of Materials Chemistry C, ISSN 2050-7526, Vol. 1, no 47, p. 7963-7972Article in journal (Refereed)
    Abstract [en]

    Magnetic nanoparticles are the functional component for magnetic membranes, but they are difficult to disperse and process into tough membranes. Here, cellulose nanofibers are decorated with magnetic ferrite nanoparticles formed in situ which ensures a uniform particle distribution, thereby avoiding the traditional mixing stage with the potential risk of particle agglomeration. The attachment of the particles to the nanofibrils is achieved via aqueous in situ hydrolysis of metal precursors onto the fibrils at temperatures below 100 °C. Metal adsorption and precursor quantification were carried out using Induction Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). FE-SEM was used for high resolution characterization of the decorated nanofibers and hybrid membranes, and TEM was used for nanoparticle size distribution studies. The decorated nanofibers form a hydrocolloid. Large (200 mm diameter) hybrid cellulose/ferrite membranes were prepared by simple filtration and drying of the colloidal suspension. The low-density, flexible and permanently magnetized membranes contain as much as 60 wt% uniformly dispersed nanoparticles (thermogravimetric analysis data). Hysteresis magnetization was measured by a Vibrating Sample Magnetometer; the inorganic phase was characterized by XRD. Membrane mechanical properties were measured in uniaxial tension. An ultrathin prototype loudspeaker was made and its acoustic performance in terms of output sound pressure was characterized. A full spectrum of audible frequencies was resolved.

  • 7. Gebauer, Denis
    et al.
    Oliynyk, Vitaliy
    Salajkova, Michaela
    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.
    Sort, Jordi
    KTH, School of Biotechnology (BIO), Glycoscience.
    Zhou, Qi
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Bergstrom, Lennart
    Salazar-Alvarez, German
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    A transparent hybrid of nanocrystalline cellulose and amorphous calcium carbonate nanoparticles2011In: NANOSCALE, ISSN 2040-3364, Vol. 3, no 9, p. 3563-3566Article in journal (Refereed)
    Abstract [en]

    Nanocellulose hybrids are promising candidates for biodegradable multifunctional materials. Hybrids of nanocrystalline cellulose (NCC) and amorphous calcium carbonate (ACC) nanoparticles were obtained through a facile chemical approach over a wide range of compositions. Controlling the interactions between NCC and ACC results in hard, transparent structures with tunable composition, homogeneity and anisotropy.

  • 8.
    Hamedi, Mahiar M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hajian, Alireza
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Fall, Andreas B.
    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.
    Håkansson, Karl
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Salajkova, Michaela
    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.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    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.
    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.
    Highly Conducting, Strong Nanocomposites Based on Nanocellulose-Assisted Aqueous Dispersions of Single-Wall Carbon Nanotubes2014In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 8, no 3, p. 2467-2476Article in journal (Refereed)
    Abstract [en]

    It is challenging to obtain high-quality dispersions of single-wall nanotubes (SWNTs) in composite matrix materials, in order to reach the full potential of mechanical and electronic properties. The most widely used matrix materials are polymers, and the route to achieving high quality dispersions of SWNT is mainly chemical functionalization of the SWNT. This leads to increased cost, a loss of strength and lower conductivity. In addition full potential of colloidal self-assembly cannot be fully exploited in a polymer matrix. This may limit the possibilities for assembly of highly ordered structural nanocomposites. Here we show that nanofibrillated cellulose (NFC) can act as an excellent aqueous dispersion agent for as-prepared SWNTs, making possible low-cost exfoliation and purification of SWNTs with dispersion limits exceeding 40 wt %. The NFC:SWNT dispersion may also offer a cheap and sustainable alternative for molecular self-assembly of advanced composites. We demonstrate semitransparent conductive films, aerogels and anisotropic microscale fibers with nanoscale composite structure. The NFC:SWNT nanopaper shows increased strength at 3 wt % SWNT, reaching a modulus of 133 GPa, and a strength of 307 MPa. The anisotropic microfiber composites have maximum conductivities above 200 S cm(-1) and current densities reaching 1400 A cm(-2).

  • 9. Lagerwall, J. P. F.
    et al.
    Schütz, Christina
    Salajkova, Michaela
    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.
    Noh, J.
    Park, J. H.
    Scalia, G.
    Bergström, L.
    Cellulose nanocrystal-based materials: From liquid crystal self-assembly and glass formation to multifunctional thin films2014In: NPG Asia Materials, ISSN 1884-4049, Vol. 6, no 1, p. e80-Article, review/survey (Refereed)
    Abstract [en]

    Cellulose nanocrystals (CNCs), produced by the acid hydrolysis of wood, cotton or other cellulose-rich sources, constitute a renewable nanosized raw material with a broad range of envisaged uses: for example, in composites, cosmetics and medical devices. The intriguing ability of CNCs to self-organize into a chiral nematic (cholesteric) liquid crystal phase with a helical arrangement has attracted significant interest, resulting in much research effort, as this arrangement gives dried CNC films a photonic band gap. The films thus acquire attractive optical properties, creating possibilities for use in applications such as security papers and mirrorless lasing. In this critical review, we discuss the sensitive balance between glass formation and liquid crystal self-assembly that governs the formation of the desired helical structure. We show that several as yet unclarified observations - some constituting severe obstacles for applications of CNCs - may result from competition between the two phenomena. Moreover, by comparison with the corresponding self-assembly processes of other rod-like nanoparticles, for example, carbon nanotubes and fd virus particles, we outline how further liquid crystal ordering phenomena may be expected from CNCs if the suspension parameters can be better controlled. Alternative interpretations of some unexpected phenomena are provided, and topics for future research are identified, as are new potential application strategies.

  • 10.
    Medina, Lilian
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Biocomposites. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Ansari, Farhan
    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.
    Carosio, Federico
    Salajkova, Michaela
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Biocomposites. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Nanocomposites from Clay, Cellulose Nanofibrils, and Epoxy with Improved Moisture Stability for Coatings and Semi-Structural Applications2019In: ACS Applied Nano Materials, E-ISSN 2574-0970Article in journal (Refereed)
    Abstract [en]

    A new type of high reinforcement content clay-cellulose-thermoset nanocomposite was proposed, where epoxy precursors diffused into a wet porous clay-nanocellulose mat, followed by curing. The processing concept was scaled to > 200 µm thickness composites, the mechanical properties were high for nanocomposites and the materials showed better tensile properties at 90% RH compared with typical nanocellulose materials. The nanostructure and phase distributions were studied using transmission electron microscopy; Young’s modulus, yield strength, ultimate strength and ductility were determined as well as moisture sorption, fire retardancy and oxygen barrier properties. Clay and cellulose contents were varied, as well as the epoxy content. Epoxy had favorable effects on moisture stability, and also improved reinforcement effects at low reinforcement content. More homogeneous nano- and mesoscale epoxy distribution is still required for further property improvements. The materials constitute a new type of three-phase nanocomposites, of interest as coatings, films and as laminated composites for semi-structural applications.

  • 11.
    Morimune-Moriya, Seira
    et al.
    Chubu Univ, Coll Engn, Dept Appl Chem, Matsumoto, Nagano 4878501, Japan..
    Salajkova, Michaela
    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.
    Zhou, Qi
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Biotechnology (BIO).
    Nishino, Takashi
    Kobe Univ, Grad Sch Engn, Dept Chem Sci & Engn, Kobe, Hyogo 6578501, Japan..
    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.
    Reinforcement Effects from Nanodiamond in Cellulose Nanofibril Films2018In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 19, no 7, p. 2423-2431Article in journal (Refereed)
    Abstract [en]

    Although research on nanopaper structures from cellulose nanofibrils (CNFs) is well established, the mechanical behavior is not well understood, especially not when CNF is combined with hard nanoparticles. Cationic CNF (Q-CNF) was prepared and successfully decorated by anionic nanodiamond (ND) nanoparticles in hydrocolloidal form. The Q-CNF/ND nanocomposites were filtered from a hydrocolloid and dried. Unlike many other carbon nano composites, the QCNF/ND nanocomposites were optically transparent. Reinforcement effects from the nanodiamond were remarkable, such as Young's modulus (9.8 -> 16.6 GPa) and tensile strength (209.5 -> 277.5 MPa) at a content of only 1.9% v/v of ND, and the reinforcement mechanisms are discussed. Strong effects on CNF network deformation mechanisms were revealed by loading unloading experiments. Scratch hardness also increased strongly with increased addition of ND.

  • 12.
    Mushi, Ngesa Ezekiel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Butchosa, Nuria
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Salajkova, Michaela
    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. KTH, School of Biotechnology (BIO), Glycoscience.
    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.
    Nanostructured membranes based on native chitin nanofibers prepared by mild process2014In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 112, p. 255-263Article in journal (Refereed)
    Abstract [en]

    Procedures for chitin nanofiber or nanocrystal extraction from Crustaceans modify the chitin structure significantly, through surface deacetylation, surface oxidation and/or molar mass degradation. Here, very mild conditions were used to disintegrate chitin fibril bundles and isolate low protein content individualized chitin nanofibers, and prepare nanostructured high-strength chitin membranes. Most of the strongly 'bound' protein was removed. The degree of acetylation, crystal structure as well as length and width of the native chitin microfibrils in the organism were successfully preserved. Atomic force microscopy and scanning transmission electron microscopy, showed chitin nanofibers with width between 3 and 4 nm. Chitin membranes were prepared by filtration of hydrocolloidal nanofiber suspensions. Mechanical and optical properties were measured. The highest data so far reported for nanostructured chitin membranes was obtained for ultimate tensile strength, strain to failure and work to fracture. Strong correlation was observed between low residual protein content and high tensile properties and the reasons for this are discussed.

  • 13. Polacek, Petr
    et al.
    Salajkova, Michaela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Jancar, Josef
    The shear adhesion strength between the FRC substructure and denture base resin: Effects of FRC architecture, adhesive composition and hydrolytic degradation2013In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 77, p. 22-28Article in journal (Refereed)
    Abstract [en]

    The adhesion strength between fiber reinforced composite (FRC) members and denture-base resin is pivotal for enhancing removable denture long lasting performance and patient comfort. FRC reinforcing rods based on glass fibers impregnated with light curing resin were used to model the FRC substructure. The influence of fiber architecture and adhesive layer composition on the shear adhesion strength, tau(a). between the FRC and denture-base resin was investigated both dry and in moist environment to assess the stability of the adhesive bond in the oral cavity. The obtained results suggest that for a given fiber architecture, adhesive composition and test conditions, the wetting of the FRC surface was the primary variable affecting the tau(a). In the case of good wetting and formation of adhesive bond between the substrates, interlaminar shear strength of the unidirectional FRC substrate was the limiting factor. In multidirectional FRC substrate, the shear strength of the outer resin rich layer was limiting factor for the maximum adhesion strength.

  • 14.
    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.

  • 15.
    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)
  • 16.
    Salajkova, Michaela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Brno University of Technology, Czech Republic .
    Sehaqui, Houssine
    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. KTH, School of Biotechnology (BIO), Glycoscience.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Nanostructured composite materials from microfibrillated cellulose and carbon nanotubes2009In: ICCM-17 17th International Conference on Composite Materials, 2009Conference paper (Refereed)
    Abstract [en]

    Thin composite films were prepared from the mixture of the aqueous suspension of microfibrillated cellulose (MFC) and multi-walled carbon nanotubes (MWCNTs). The morphology, electrical conductivity, and mechanical properties of the composites were characterized. Good electrical properties were obtained when the MWCNTs content was higher than 2 wt%.

  • 17.
    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.

  • 18.
    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.

  • 19.
    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.

  • 20.
    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)
  • 21.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Mushi, Ngesa Ezekiel
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Morimune, Seira
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Salajkova, Michaela
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Nishino, Takashi
    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.
    Cellulose Nanofiber Orientation in Nanopaper and Nanocomposites by Cold Drawing2012In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 4, no 2, p. 1043-1049Article in journal (Refereed)
    Abstract [en]

    To exploit the mechanical potential of native cellulose fibrils, we report on the preparation of nanopaper with preferred orientation of nanofibrillated cellulose (TEMPO-NFC) by cold drawing. The preparation route is papermaking-like and includes vacuum filtering of a TEMPO-oxidated NFC water dispersion, drawing in wet state and drying. The orientation of the fibrils in the nanopaper was assessed by AFM and wide-angle Xray diffraction analysis, and the effect on mechanical properties of the resulting nanopaper structure was investigated by tensile tests. At high. draw ratio, the degree of orientation is as high as 82 and 89% in and cross-sectional planes of the nanopaper, respectively, and the Young's modulus is 33 GPa. This is much higher than mechanical properties of isotropic nanopaper. The cold drawing method can be also applied to NFC nanocomposites as demonstrated, by preparation of TEMPO-NFC/hydroxyethyl cellulose (HEC) nanocomposites. The introduction of the soft HEC matrix allows further tailoring of the mechanical properties.

  • 22.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Salajkova, Michaela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Brno University of Technology, Czech Republic .
    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.
    Biomimetic aerogels from microfibrillated cellulose and xyloglucan2009In: ICCM-17 17th International Conference on Composite Materials, 2009Conference paper (Refereed)
    Abstract [en]

    Cellulose aerogels with density of 7-100 kg/m3 were prepared by freeze drying from microfibrillated cellulose water suspensions, and biomimetic aerogels were prepared with the addition of xyloglucan. Their microstructures and physical properties were characterized by scanning electron microscopy, nitrogen adsorption measurements, and tensile tests.

  • 23.
    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.

1 - 23 of 23
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