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  • 1.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Sparnins, Edgars
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Strength distribution of elementary flax fibres2005In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 65, no 3-4, p. 693-702Article in journal (Refereed)
    Abstract [en]

    Flax fibres, along with a number of other natural fibres, are being considered as an environmentally friendly alternative of synthetic fibres in fibre-reinforced polymer composites. A common feature of natural fibres is a much higher variability of mechanical properties. This necessitates study of the flax fibre strength distribution and efficient experimental methods for its determination. Elementary flax fibres of different gauge lengths are tested by single fibre tension in order to obtain the stress-strain response and strength and failure strain distributions. The applicability of single fibre fragmentation test for flax fibre failure strain and strength characterization is considered. It is shown that fibre fragmentation test can be used to determine the fibre length effect on mean fibre strength and limit strain.

  • 2. Arab, A.
    et al.
    Stommel, M.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rack, A.
    Investigation of fibre degradation in natural fibre reinforced biocomposites2013In: Proceedings of the 5th International Conference on Sustainable Materials, Polymers and Composites: Ecocomp 2013, 2013, p. 174-185Conference paper (Refereed)
  • 3. Arab, A.
    et al.
    Stommel, M.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Stiffness prediction in green composites using homogenization techniques2013In: Proceedings of the 19th International Conference on Composite Materials: ICCM 2013, Montreal (Canada), 2013, p. 1214-1222Conference paper (Refereed)
  • 4.
    Arab, Asghar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Stommel, L.
    Saarland University.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fibre Orientation Investigation in Short Natural Fibre Reinforced Composites Using Synchrotron Imaging2013Conference paper (Refereed)
  • 5.
    Bjurhager, Ingela
    et al.
    Kungliga tekniska högskolan, KTH.
    Ljungdahl, Jonas
    Kungliga tekniska högskolan, KTH.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gamstedt, Kristofer
    Kungliga tekniska högskolan, KTH.
    Berglund, Lars A
    Kungliga tekniska högskolan, KTH.
    Towards improved understanding of PEG-impregnated waterlogged archaeological wood: a model study on recent oak2010In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 64, no 2, p. 243-250Article in journal (Refereed)
    Abstract [en]

    To prevent deformation and cracking of waterlogged archaeological wood, polyethylene glycol (PEG) as a bulk impregnation agent is commonly applied. PEG maintains the wood in a swollen state during drying. However, swelling of wood can reduce its mechanical properties. In this study, the cellular structure of oak and cell wall swelling was characterized by scanning electron microscopy (SEM) of transverse cross-sections, and the microfibril angle of oak fibers was determined by wide angle X-ray scattering (WAXS). Samples of recent European oak (Quercus robur L) impregnated with PEG (molecular weight of 600) were tested in axial tension and radial compression. Mechanical tests showed that axial tensile modulus and strength were only slightly affected by PEG, whereas radial compressive modulus and yield strength were reduced by up to 50%. This behavior can be explained by the microstructure and deformation mechanisms of the material. Microfibril angles in tensile test samples were close to zero. This implies tensile loading of cellulose microfibrils within the fiber cell walls without almost any shear in the adjacent amorphous matrix. These results are important because they can help separate the impact of PEG on mechanical properties from that of chemical degradation in archaeological artifacts, which display only small to moderate biological degradation.

  • 6.
    Gopalakrishnan, Preetha
    et al.
    L'Equipe Caracté Risation des Amorphes et Polymères (LECAP) de la FRE 3101, Polymè Res, Biopolymè Res, Surface (PBS), Faculté des Sciences, Avenue de l'Université, Saint Etienne du Rouvray.
    Enqvist, Evelina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gatlin, Richard
    L'Equipe Caracté Risation des Amorphes et Polymères (LECAP) de la FRE 3101, Polymè Res, Biopolymè Res, Surface (PBS), Faculté des Sciences, Avenue de l'Université, Saint Etienne du Rouvray.
    Saiter, Jean Marc
    L'Equipe Caracté Risation des Amorphes et Polymères (LECAP) de la FRE 3101, Polymè Res, Biopolymè Res, Surface (PBS), Faculté des Sciences, Avenue de l'Université, Saint Etienne du Rouvray.
    A new green thermoplastic polymer with improved hydrophobic character2010In: Macromolecular Symposia, ISSN 1022-1360, E-ISSN 1521-3900, Vol. 290, no 1, p. 25-29Article in journal (Refereed)
    Abstract [en]

    A green thermoplastic polymer based on wheat flour was modified by the addition of a natural crosslinker genipin. Films of the polymer modified with different composition of genipin were prepared by extrusion. Free surface energy using contact angle method, moisture absorption test and hardness test were used to characterize the products. From moisture absorption and contact angle measurements, it was seen that for genipin amounts higher than 0.2% w/w, a hydrophobic character is achieved. Results obtained indicate enhancement in hydrophobic properties of the films.

  • 7.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaddami, H.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Design and characterization of cellulose fibers with hierarchical structure for polymer reinforcement2013Conference paper (Refereed)
    Abstract [en]

    This paper describes an approach to manufacture hierarchical composites from environmentally friendly materials by grafting cellulose whiskers onto regenerated cellulose fibers (Cordenka 700). Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy and X-ray diffraction analysis were performed to verify the degree of modification. The mechanical properties of the unmodified and modified fibers were analyzed using fiber bundle tensile static and loading-unloading tests. To show the effect of cellulose whiskers grafting on the Cordenka fibers, epoxy based composites were manufactured and tensile tests done on transverse uni-directional specimens. The mechanical properties were significantly increased by fiber modification and addition of the nano-phase into composite reinforced with micro-sized fibers.

  • 8.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaddami, Hamid
    Cadi Ayyad University, Faculty of Sciences and Techniques.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Design and characterization of cellulose fibers with hierarchical structure for polymer reinforcement2013In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 20, no 6, p. 2765-2778Article in journal (Refereed)
    Abstract [en]

    This paper describes an approach to manufacture hierarchical composites from environmentally friendly materials by grafting cellulose whiskers onto regenerated cellulose fibers (Cordenka 700). Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy and X-ray diffraction analysis were performed to verify the degree of modification. The mechanical properties of the unmodified and modified fibers were analyzed using fiber bundle tensile static and loading-unloading tests. To show the effect of cellulose whiskers grafting on the Cordenka fibers, epoxy based composites were manufactured and tensile tests done on transverse uni-directional specimens. The mechanical properties were significantly increased by fiber modification and addition of the nano-phase into composite reinforced with micro-sized fibers.

  • 9.
    Hajlane, Abdelghani
    et al.
    University Cadi Ayyad of Marrakech.
    Sahib, Anas
    University Cadi Ayyad of Marrakech.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Kaddami, Hamid
    University Cadi Ayyad of Marrakech.
    Design and characterization of cellulose fibers with highly hierarchical structure2010Conference paper (Other academic)
  • 10.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Andersons, J.
    Sparnins, Edgars
    Wallström, Lennart
    Cellulose-based fibers and their polymer composites characterization and prediction of properties2005In: 8th International Conference on Woodfiber-Plastic Composites (and Other Natural Fibers): May 23 - 25, 2005, Monona Terrace Community & Convention Center, Madison, Wisconsin, USA, Madison, Wis., 2005, p. 25-36Conference paper (Refereed)
  • 11.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Andersons, J.
    Institute of Polymer Mechanics, University of Latvia.
    Wallström, Lennart
    Interfacial shear strength of flax fiber/thermoset polymers estimated by fiber fragmentation tests2005In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 40, no 9-10, p. 2721-2722Article in journal (Refereed)
    Abstract [en]

    We study flax/thermoset polymer ISS [interfacial shear strength] for most common types of thermosets: vinylester, polyester, and epoxy. The effect of fiber surface treatment on ISS in such systems reinforced with flax fibers is investigated. Apparent ISS is evaluated from SFF tests by the Kelly-Tyson approach utilizing fiber strength at the critical length. Fiber strength at such small lengths is hardly accessible to direct testing, therefore it is usually extrapolated from test results at larger gauge lengths. We present ISS of flax fibers subjected to different treatments and thermoset polymers, derived from SFF tests using comprehensive fiber strength data.

  • 12.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Andersons, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Sparnins, Edgars
    Wallström, Lennart
    Flax fibres for structural composites2003Conference paper (Other academic)
  • 13.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Andersons, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Wallström, Lennart
    Single fiber fragmentation experiment performed on flax fibers2006In: Experimental techniques and design in composite materials (ETDCM6): ["Sixth International Seminar on Experimental Techniques and Design in Composite Materials" wich was held at Padova in June 2003] / [ed] Marino Quaresimin, Amsterdam: Elsevier, 2006Conference paper (Other academic)
  • 14.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Andersons, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Wallström, Lennart
    Strength and adhesion characteristics of elementary flax fibres with different surface treatments2003In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 34, no 7, p. 603-612Article in journal (Refereed)
    Abstract [en]

    It is known that the best flax fibres can compete in terms of mechanical properties with glass fibres. However, during the manufacturing process flax fibres are often damaged, and hence, the properties can be lowered. Furthermore, these properties change from batch to batch (depending on the time and place of harvest), which means that they are somewhat unpredictable. The most affected fibre property is strength, which can vary in very wide interval due to defects introduced by the manufacturing process. Therefore, there is a need for a simple but reliable testing procedure that allows the estimation of the strength of flax fibres, so called quality control. Regarding the final goal, that is the development of natural fibre composites, another crucial property is the fibre/matrix adhesion. The objective of this study is to investigate the possibility to use the single fibre fragmentation test to characterize strength distribution of flax fibres and to evaluate the adhesion. Untreated flax fibres and fibres coated by a special surface treatment are used. Fragmentation tests are performed on flax fibres embedded in thermoset, vinylester and polyester, resins. Results show that there is a definite improvement in interfacial strength when a fibre surface treatment is applied. Fibre strength distribution is obtained from SFFT and compared with limited results available from single flax fibre tests.

  • 15.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Andersons, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Wallström, Lennart
    Strength distribution of flax fibers obtained from single fiber fragmentation test2002In: Book of abstracts / Twelfth International Conference Mechanics of Composite Materials, June 9 - 13, 2002, Riga, Latvia / [ed] V. Tamuzs, 2002Conference paper (Other academic)
  • 16.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Flax fibers for structural composites: characterization and properties2003In: Book of abstracts: International Workshop on Natural Fiber Composites, 2003Conference paper (Other academic)
  • 17.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Berglund, Lars
    Luleå tekniska universitet.
    Natural fiber composites based on flax - matrix effects2001In: Modelling for saving resources: International scientific colloquium MSR 2001. Riga, May 17 - 18, 2001 : proceedings / University of Latvia, 2001Conference paper (Refereed)
  • 18.
    Katerelos, Dionisis
    et al.
    LTU, TFM, Polymerteknik.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Labou, Diamantoula
    FORTH/ICE-HT, Patras.
    Wallström, Lennart
    Effect of stretching on the mechanical performance of polypropylenedoped with multi-wall carbon nanotubes2008Conference paper (Other academic)
  • 19.
    Katerelos, Dionysios
    et al.
    LTU.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Labou, D.
    FORTH/ICE-HT, Patras.
    Wallström, Lennart
    Alteration of the mechanical behaviour of polypropylene owing to successive introduction of multiwall carbon nanotubes and stretching2009In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 45, no 4, p. 423-434Article in journal (Refereed)
    Abstract [en]

    Stretching effects on the morphology of polypropylene/carbon nanotube composites is the focus of this work. The material under investigation was composed of isotactic polypropy lene (iPP) and multiwall car bon nanotubes (MWCNTs) in amount of 0.5 wt.%. The iPP and CNTs were mixed under sonication in a solvent, and the homogenized mixture was melted and pressed. The rectangular plates produced from the material were stretched by a constant load at a fixed temperature in order to obtain extended specimens. The scanning electron microscopy, a thermal gravimetric analysis, and the differential scanning calorimetry were employed to study variations in the structural morphology of the material. A dynamic mechanical analysis showed that the strain-induced crystallization of polypropylene and the possible Stone-Wales transformation of the carbon nanotubes due to stretching improved the mechanical performance of the nanocomposites considered.

  • 20. Katerelos, Dionysos
    et al.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Labou, D.
    FORTH/ICE-HT, Patras.
    Wallström, Lennart
    FORTH/ICE-HT, Patras.
    Erratum: Alteration of the mechanical behaviour of polypropylene owing to successive introduction of multiwall carbon nanotubes and stretching2009In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 45, no 5, p. 543-Article in journal (Other academic)
  • 21.
    Mannberg, Peter
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Nyström, Birgitha
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Service life assessment and moisture influence on bio-based composites2014In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, no 15, p. 5265-5270Article in journal (Refereed)
    Abstract [en]

    A race towards a more sustainable society is going on worldwide and decreasing dependence on fossil resources in energy and transport sectors is main goals. One path to decreased oil usage is development of lightweight materials from renewable resources like bio-based composites. However these new bio-based materials have not only to compete in mechanical performance, they also have to restrain environmental loads like moisture and temperature over time. In this study two bio-based composites have been compared to an oil-based composite in terms of long-term properties and water absorption behaviour. The long-term behaviour is determined by dynamic mechanical thermal analysis, DMTA, and time temperature superposition, TTSP. The water uptake is determined by submersion of specimens into water and tracking their weight change over time. The moisture influence is characterised in form of water uptake and change in the master curves created by TTSP procedure. The results show that there is a significant difference in long-term performance between the bio-based and oil-based composites. It is realized that the bio-based composites can be a good alternative for some applications especially when taking their eco-friendly nature into account.

  • 22. Marklund, Erik
    et al.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Nonlinear viscoelasticity and viscoplasticity of flax/polypropylene composites2006In: Journal of engineering materials and technology, ISSN 0094-4289, E-ISSN 1528-8889, Vol. 128, no 4, p. 527-536Article in journal (Refereed)
    Abstract [en]

    In tensile tests the flax/polypropylene composites clearly show nonlinear behavior in loading and hysteresis loops in unloading. In creep tests performed at different load levels the response was nonlinear viscoelastic, and after recovery, viscoplastic strains were detected. No degradation in stiffness could be seen and thus nonlinear viscoelasticity and viscoplasticity were assumed to be the main cause for the observed behavior. The fracture surface of a specimen that experienced creep rupture at 24 MPa was investigated using a scanning electron microscope. The viscoplastic response was studied experimentally and described by a power law with respect to time and stress level in the creep test. The nonlinear viscoelasticity was described using Schapery's model. The application of Prony series and a power law to approximate the viscoelastic compliance was investigated. Both descriptions have accuracy sufficient for practical applications. However, at high stresses the attempts to describe the viscoelastic compliance by a power law with a stress-independent exponent failed and therefore stress dependence of this exponent was included in the data analysis. The accuracy within the considered stress range is good, but the thermodynamic consistency of this procedure has to be proven.

  • 23.
    Nättinen, Kalle
    et al.
    VTT Technical Research Centre of Finland, Espoo.
    Hyvärinen, Sari
    VTT Technical Research Centre of Finland, Espoo.
    Joffe, Roberts
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Madsen, Bo
    Department of Materials Research, Riso National Laboratory for Sustainable Energy, Technical University of Denmark.
    Naturally compatible: starch acetate/cellulosic fibre composites. Part I: Processing and properties2010In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 31, no 3, p. 524-535Article in journal (Refereed)
    Abstract [en]

    Composite compounds based on hemp and flax fibers in triethyl citrate plasticized starch acetate were prepared by melt processing. For better properties and processability, compounds with plasticizer contents in the range 20-35 wt% were screened. Composites were prepared with fiber contents up to 50 wt%. The composite mechanical properties were measured from injection molded test specimens. A Young's modulus of 8.3 GPa and stress at maximum load of 51 MPa were obtained with 40 wt% flax fiber in a plasticized starch acetate with 20 wt% triethyl citrate. Decreasing the plasticizer and increasing the fiber content, the tensile properties were consistently improved. An almost linear relation between fiber content and the tensile properties was found. The increase of the fiber content first improved the impact strength, but at higher fiber contents resulted in a reduction of impact strength. The quality of the produced materials was found to be good; the variation in properties between duplicated compounds was acceptable low, the variation in density and fiber content along a single tensile specimen was low, and finally, the porosity content was low even at high fiber content. The latter result was verified with scanning electron microscope images of fracture surfaces of the composites.

  • 24.
    Nättinen, Kalle
    et al.
    VTT.
    Lampinen, Johanna
    VTT.
    Madsen, Bo
    Risø, DTU.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Varna, Janis
    Starch acetate N-fibre composites2008In: 13th European Conference on Composite Materials: 2-5 June 2008, Stockholm, Sweden, 2008Conference paper (Refereed)
    Abstract [en]

    Cellulosic fibre composite compounds based on hemp and flax fibres in triethyl citrate plasticised starch acetate were prepared by melt processing. Composites were prepared with fibre contents up to 50w%. A stiffness of 8.3 GPa and stress at maximum load of 51 MPa were obtained with 40w% flax fibre in a plasticised starch acetate with 20w% triethyl citrate. An almost linear relation between fibre content and the tensile properties was found. The impact strength of the composites was increased with the plasticiser content. The porosity content was low even at high fibre content.

  • 25.
    Oksman, Kristiina
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Lars A.
    Luleå tekniska universitet.
    Filho, Romildo Dias Toledo
    Federal University of Rio de Janeiro.
    Morphology and mechanical properties of unidirectional sisal-epoxy composites2002In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 84, no 13, p. 2358-2365Article in journal (Refereed)
    Abstract [en]

    Plant fibers are of increasing interest for use in composite materials. They are renewable resources and waste management is easier than with glass fibers. In the present study, longitudinal stiffness and strength as well as morphology of unidirectional sisal-epoxy composites manufactured by resin transfer molding (RTM) were studied. Horseshoe-shaped sisal fiber bundles (technical fibers) were nonuniformly distributed in the matrix. In contrast to many wood composites, lumen was not filled by polymer matrix. Technical sisal fibers showed higher effective modulus when included in the composite material than in the technical fiber test (40 GPa as compared with 24 GPa). In contrast, the effective technical fiber strength in the composites was estimated to be around 400 MPa in comparison with a measured technical fiber tensile strength of 550 MPa. Reasons for these phenomena are discussed

  • 26.
    Oksman, Kristiina
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Lars
    Luleå tekniska universitet.
    Filho, R.D.T.
    Mechanical properties and morphology of sisal fiber-epoxy composites2000In: Proceedings from the Third International Symposium on Natural Polymers and Composites and the Workshop on Progress in Production and Processing of Cellulosic Fibres and Natural Polymers: São Pedro, 14-17 May 2000, São Carlos: Embrapa Instrumentacao Agropecuaria , 2000Conference paper (Refereed)
  • 27. Sparnins, Edgars
    et al.
    Andersons, J.
    Joffe, Roberts
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mechanical properties of flax fibres and composites2005In: Proceedings ICSAM 2005, 2005, p. 47-54Conference paper (Refereed)
  • 28. Sparnins, Edgars
    et al.
    Andersons, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mechanical properties of elementary flax fibers and flax-fiber composites2004In: Mechanics of composite materials: XIII international conference, May 16 - 20, 2004, Riga ; MCM 2004, 2004Conference paper (Other academic)
  • 29.
    Thuvander, Fredrik
    et al.
    Luleå tekniska universitet.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Lars A.
    Luleå tekniska universitet.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Effects of an impregnation procedure for prevention of wood cell wall damage due to drying2001In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 34, no 6, p. 473-480Article in journal (Refereed)
    Abstract [en]

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

  • 30.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Cell wall bulking and distribution of different chemicals in pine, Pinus Sylvestris1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The interaction between wood, Pinus sylvestris, (60% RH) and polyethyleneglycol (PEG) of different molecular weights (PEG 200 and PEG 1500), pentaerythritol and glycerol, impregnated into the wood, has been investigated using Scanning Electron Microscopy, EDS-analysis, dynamical mechanical techniques (DMTA), X-ray diffraction (WAXS) and macroscopic dimensional measurement. Reduced dimensional changes after impregnation when exposed to environments with changing moisture content, showed that the stabilization effect of glycerol and PEG 200 impregnation is very good. The other chemicals used, especially pentaerythritol, were not as effective as glycerol and PEG 200. Cell wall measurements using SEM show that an increase in cell wall thickness gives a corresponding increase in stabilization effect. DMTA-measurements showed that interaction between wood molecules and the chemicals used differs. In general, a higher degree of cell wall penetration of the chemicals gives a better stabilization effect. WAXS- investigations showed free crystalline pentaerythritol, PEG 1500, glycerol and PEG 200. Examination using SEM/EDS-linescan of potassium stained chemicals confirmed the results from the cell wall thickness measurements. However, the better resolution obtained in the STEM/EDS-linescan showed an inhomogenous distribution of the chemical in the cell wall. High temperature dried and green wood of Swedish pine was impregnated with glycerate and silver nitrate. Silver was precipitated in the cell wall by a new method. A significant difference in the distribution, size and location of the silver was observed. The silver particles are small and dispersed in the green wood samples but clustered and irregulary spaced in the dried specimens. The inhomogenous distribution in the dried specimens is believed to be the result of damage inside the wood cell walls due to drying stresses, which in turn will negatively affect the dimensional stabilizing result. The strength and energy to fracture is increased by a factor of two if wood not is allowed to be dried before cell wall bulking. This is because the impregnating chemical (glycerol in the present case) in the cell wall substitutes some of the moisture and therefore limits drying stresses. The glycerol is believed to be soluble inbetween the hemicellulose. The average distance between the silver particles in the impregnated green wood indicates that the impregnant is distributed in the cell wall at the microfibrilar level. Experimental results showed that the fastest diffusion path into the cell wall is from the lumen over the pit membrane through the compound middle lamell and not from the lumen through the secondary wall layer S3. The darker compound middle lamella seen in TEM is believed to be an artefact, as it is possible that the ML is thicker than the other layers in the wood cell wall after microtoming.

  • 31.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Wood surface stabilization1994Licentiate thesis, comprehensive summary (Other academic)
  • 32.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Diffusion, size and location of added silver grains in the cell walls of Swedish pine, Pinus sylvestris2000In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 34, no 5, p. 403-415Article in journal (Refereed)
    Abstract [en]

    The size and location of silver particles in K-glycerate/AgNO3 impregnated Swedish pine, green wood as well as high temperature dried, have been studied using TEM micrographs. The diameter of the silver particles was found to be 2-20 nm in the impregnated green wood and as large as 1000 nm (major axis) for the ellipsoid-shaped silver clusters in the impregnated dried wood. Studying the projected area of the silver particles in impregnated green wood indicated that there are a lot of particles (40%) in the compound middle lamella with fewer particles in the S2 (6-8%), S1 (4%) and S3 (2%) layers. The average distance between the silver particles, 50 nm (S2-layer), in impregnated green wood shows that the impregnant is distributed in the cell wall at the microfibrilar level. Experimental results show that the fastest diffusion path into the cell wall is from the lumen over the pit membrane through the compound middle lamella and not from the lumen through the secondary wall layer S3.

  • 33.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Distribution of added chemicals in the cell walls of high temperature dried and green wood of Swedish pine, Pinus sylvestris2000In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 34, no 4, p. 327-336Article in journal (Refereed)
    Abstract [en]

    High temperature dried and green wood of Swedish pine was impregnated with glycerate and silver nitrate. TEM and STEM/EDS on ultramicrotomed specimens was used to reveal the location of silver in the cell wall. The silver was precipitated by a new method using silver nitrate impregnated after which the wood had been impregnated with potassium glycerate. A significant difference in the distribution of the silver was observed. In the green wood, there was a homogenous distribution of the impregnant compared to the dried specimens. The inhomogenous distribution in the dried specimens is believed to be the result of damage inside the wood cell walls which in turn will have a negative effect on dimensional stabilizing results. The darker compound middle lamella observed is believed to be an artefact.

  • 34.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Measurement of cell wall penetration in wood of water-based chemicals using SEM/EDS and STEM/EDS technique1999In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 33, no 2, p. 111-122Article in journal (Refereed)
    Abstract [en]

    The penetration of bulking chemicals (glycerol, PEG 200, PEG 1500 and pentaerythritol) into the cell wall of wood, Pinus sylvestris, has been studied. A number of different methods for determining the distribution of chemicals in the cell wall were used. Measurements of the increase in cell wall thickness showed that glycerol and PEG 200 resulted in greater cell wall bulking compared to PEG 1500 and pentaerythritol. Examination with SEM/EDS-linescan confirmed these results. However, the better resolution possible with the STEM/EDS-linescan revealed an inhomogenous distribution of the chemical in the cell wall. This is believed to be due to microcracks in the cell wall which are the result of the initial drying of the wood. This general damage to the cell wall could be the reason for the failure to find a stabilizing chemical and method.

  • 35.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Wood surface stabilization with polyethyleneglycol, PEG1995In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 29, no 2, p. 109-119Article in journal (Refereed)
    Abstract [en]

    The possibilities of interaction between wood, Pinus sylvestris, (60% RH) and potassium stained PEG 1500 (polyethyleneglycol) have been investigated using Scanning Electron Microscopy (EDS-analysis), dynamical mechanical techniques (DMTA) and X-ray diffraction (WAX). The EDS-analysis shows an even distribution of potassium in the cell wall. On the other hand the predicted cell wall swelling associated with PEG absorption is absent. This indicates that the method of staining PEG with potassium does not work. The DMTA-measurements show interaction on the molecular level between wood and PEG 1500. EDS-analysis, SEM- and WAX-investigations show free PEG in the impregnated specimens.

  • 36.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Ytstabilisering: kvalitetshöjning för träprodukter1995Report (Other academic)
  • 37.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, K.A.H.
    Luleå tekniska universitet.
    Johansson, Ingvar
    Wood surface stabilization1995In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 53, no 2, p. 87-92Article in journal (Refereed)
    Abstract [en]

    The interaction between wood, Pinus sylvestris (60% RH), and polyethyleneglycol (PEG) of different molecular weights (PEG 200 and PEG 1500), pentaerythritol and glycerol, impregnated into wood, has been investigated using Scanning Electron Microscopy (SEM), dynamical mechanical techniques (DMTA), X-ray diffraction (WAXS) and macroscopic dimensional measurement. Reduced dimensional changes after impregnation, in environments with changing moisture content, show that the stabilization effect of glycerol impregnation is very good. The other chemicals used, especially pentaerythritol, were not as effective as glycerol. Cell wall measurements, using SEM, show that an increase in cell wall thickness gives a corresponding increase in stabilization effect. DMTA-measurements show that interaction between wood molecules and the chemicals used differs. In general, a higher degree of cell wall penetration of the chemicals show a better stabilization effect. PEG 200 was found to penetrate the cell wall much better than PEG 1500. WAXS-investigations show free crystalline pentaerythritol, PEG 1500, glycerol and PEG 200.

  • 38.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Llindberg, Henrik
    Luleå tekniska universitet.
    Distribution of different cell wall bulking chemicals in Swedish pine1998Report (Other academic)
  • 39.
    Warnes, William H.
    et al.
    School of Mechanical, Industrial, & Manufacturing Engineering, Oregon State University.
    Kruzic, Jamie J.
    School of Mechanical, Industrial, & Manufacturing Engineering, Oregon State University.
    Pratt, Clara C.
    School of Social and Behavioral Health Sciences, Oregon State University.
    Stehr, Christian
    School of Mechanical, Industrial, & Manufacturing Engineering, Oregon State University.
    Cann, David P.
    School of Mechanical, Industrial, & Manufacturing Engineering, Oregon State University.
    Gibbons, Brady J.
    School of Mechanical, Industrial, & Manufacturing Engineering, Oregon State University.
    Gallino, Isabella
    Department of Materials Science and Engineering, Saarland University, Saarbrücken.
    Soldera, Flavio Andrés
    Department of Materials Science and Engineering, Saarland University, Saarbrücken.
    Busch, Ralf
    Department of Materials Science and Engineering, Saarland University, Saarbrücken.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Improving participation of engineering students studying abroad: an international dual-degree program in materials science and mechanical engineering2013In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 65, no 7, p. 840-845Article in journal (Refereed)
1 - 39 of 39
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