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  • 1.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gong, Guan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. RISE SICOMP.
    Nyström, Birgitha
    RISE SICOMP.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Characterization of wood and Graphene Nanoplatelets (GNPs) Reinforced Polymer CompositesManuscript (preprint) (Other academic)
  • 2.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Sparnins, Edgars
    Nyström, Birgitha
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Scale effect of the tensile strength of flax-fabric-reinforced polymer composites2011In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, no 23, p. 1969-1974Article in journal (Refereed)
    Abstract [en]

    The development of UD natural fiber composites, considered for application as structural materials, necessitates evaluation of the scale effect of their strength. Alignment of the fibers in flax bast fiber composites can be achieved by employing textile reinforcement, such as yarns and fabrics. Cutting specimens for mechanical tests out of such textile-reinforced composite plates results in a complex non-uniform reinforcement structure at their edges, which may affect the strength of specimens. Scale effect of the tensile strength in the fiber direction of flax fabric reinforced composites is studied in the current work. A model accounting for both volume and edge effect of the specimens on their tensile strength is proposed.

  • 3.
    Mannberg, Peter
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Nyström, Birgitha
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Service life assessment and moisture influence on bio-based thermosetting resins2014In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, no 10, p. 3687-3693Article in journal (Refereed)
    Abstract [en]

    In this study, three different types of bio-based resins are compared to a conventional oil-based epoxy in terms of moisture uptake, long-term properties and its influence of moisture and glass transition temperature, Tg. Moisture uptake is determined by means of gravimetric method, time temperature superposition (TTSP), and Tg data obtained in dynamic mechanical thermal analysis (DMTA). Moisture uptake show Fickian diffuison behavour for all resins, saturation level and diffusion coefficient however differ. The long-term properties is characterised by creep compliance master curves created by means of TTSP. The examined bio-based resins are compatible to the reference epoxy in term of stability up to 3–10 years. Comparison between master curves for virgin, wet, and dried material show that moisture present in the specimen increases creep rate, and that some of this increase remains after drying of samples. Tg measurements show that moisture inside the specimen decreases Tg; this is anticipated because of the plasticizing effect of water. The overall conclusions are that the bio-based resins of polyester, and epoxy type are comparable in performance with oil-based epoxy, LY556 and they can be used to develop high-performance composites

  • 4.
    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.

  • 5.
    Nyström, Birgitha
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Natural fiber composites: optimization of microstructure and processing parameters2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Natural fiber composites, (NFC) are defined in this work as a group of materials where at least the fibers originates from renewable and CO2 neutral resources. NFC consists of a polymer matrix and a natural fiber. The fibers which originate from wood or plants can replace non-renewable fibers or fillers or simply replace part of the plastic. If plastics from renewable resources are used, NFC is a 100% renewable material. Even though there is very large variety of fibers, matrices and manufacturing techniques used to produce NFC, these materials are often separated as its own material class. However, the variety of constituents and processing methods result in completely different materials with very diverse properties. NFC could thus be suitable for an extremely wide area of applications. We believe that it is important to distinguish different types of NFC and classify them based on matrix (thermoplastic or thermoset), fiber (long or short/orientation) and manufacturing techniques. For instance compression molded composites are very different from injection molded materials. Therefore it is important to find the limits of their performance in connection to the processing parameters. The focus of this work is on the compounding and injection molding techniques. Although extensive research has been done on injection molded NFC, this is one area where the natural fibers still have not made a market breakthrough. We believe that the reason for the limited use of natural fiber compound in injection molded products is partly due to uncertainties about the influence of different constituents on the final properties and lack of defined framework for product design and manufacturing in order to optimize the material and assure consistent quality. Although deep knowledge about these materials have been accumulated among producers and researchers in this area, guidelines or simple rules of thumb for NFC development and processing are quite hard to find in literature. Thus, in order to make natural fiber compounds a more interesting alternative for the injection molding industry, this work is focused on finding limitations on important properties and giving general guidelines for material optimization and processing of natural fiber composites.

  • 6. Nyström, Birgitha
    et al.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Långstöm, Runar
    SICOMP AB, Swedish Institute of Composites.
    Natural fiber composites: optimization of microstructure and processing parameters2007In: Book of abstracts: European school of materials science and engineering, fourth research conference, June 7-8, 2007, Barcelona, Spain, 2007, p. 23-Conference paper (Other academic)
  • 7.
    Pupure, Liva
    et al.
    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.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nyström, Birgitha
    Development of constitutive model for composites exhibiting time dependent properties2013In: 7th EEIGM International Conference on Advanced Materials Research: 21–22 March 2013, LTU, Luleå, Sweden, IOP Publishing Ltd , 2013, article id 12007Conference paper (Refereed)
    Abstract [en]

    Regenerated cellulose fibres and their composites exhibit highly nonlinearbehaviour. The mechanical response of these materials can be successfully described by themodel developed by Schapery for time-dependent materials. However, this model requiresinput parameters that are experimentally determined via large number of time-consuming testson the studied composite material. If, for example, the volume fraction of fibres is changed wehave a different material and new series of experiments on this new material are required.Therefore the ultimate objective of our studies is to develop model which determines thecomposite behaviour based on behaviour of constituents of the composite. This paper gives anoverview of problems and difficulties, associated with development, implementation andverification of such model.

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