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  • 1.
    Almgren, Karin M.
    et al.
    Innventia.
    Gamstedt, E. Kristofer
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Berthold, Fredrik
    Innventia.
    Lindström, Mikael
    Innventia.
    Moisture uptake and hygroexpansion of wood fiber composite materials with polylactide and polypropylene matrix materials2009In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 30, no 12, p. 1809-1816Article in journal (Refereed)
    Abstract [en]

    Effects of butantetracarboxylic acid (BTCA) modification, choice of matrix, and fiber volume fraction on hygroexpansion of wood fiber composites have been investigated. Untreated reference wood fibers and BTCA-modified fibers were used as reinforcement in composites with matrices composed of polylactic acid (PLA), polypropylene (PP), or a mixture thereof. The crosslinking BTCA modification reduced the out-of-plane hygroexpansion of PLA and PLA/PP composites, under water-immersed and humid conditions, whereas the swelling increased when PP was used as matrix material. This is explained by difficulties for the BTCA-modified fibers to adhere to the PP matrix. Fiber volume fraction was the most important parameter as regards out-of-plane hygroexpansion, with a high-fiber fraction leading to large hygroexpansion. Fiber-matrix wettability during processing and consolidation also showed to have a large impact on the dimensional stability and moisture uptake. POLYM. COMPOS., 30:1809-1816, 2009.

  • 2. Almgren, Karin M.
    et al.
    Gamstedt, E. Kristofer
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Varna, Janis
    Luleå tekniska universitet, LTU.
    Contribution of wood fiber hygroexpansion to moisture induced thickness swelling of composite plates2010In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 31, no 5, p. 762-771Article in journal (Refereed)
    Abstract [en]

    One of the main drawbacks of wood fiber-based composite materials is their propensity to swell due to moisture uptake. Because the wood fibers are usually the main contributor to hygroexpansion, it is of interest to quantify the hygroexpansion coefficient of wood fibers, to compare and rank different types of fibers. This investigation outlines an inverse method to estimate the transverse hygroexpansion coefficient of wood fibers based on measurements of moisture induced thickness swelling of composite plates. The model is based on composite micromechanics and laminate theory. Thickness swelling has been measured on polylactide matrix composites with either bleached reference fibers or crosslinked fibers. The crosslinking modification reduced the transverse hygroexpansion of the composites and the transverse coefficient of hygroexpansion of the fibers was reduced from 0.28 strain per relative humidity for reference fibers to 0.12 for cross-linked fibers

  • 3.
    Azhdar, Bruska
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Stenberg, Bengt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Polymer-nanofiller prepared by high-energy ball milling and high velocity cold compaction2008In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 29, no 3, p. 252-261Article in journal (Refereed)
    Abstract [en]

    High-energy ball milling using comilling in a solid state by low-temperature mechanical alloying to prepare nickel-ferrite (NiFe2O4) nanopowders and ultrafine poly(methyl methacrylate) (PMMA), dispersing nanoparticles in a polymer matrix, and a uniaxial high-velocity cold compaction process using a cylindrical, hardened steel die and a new technique with relaxation assists have been studied. The focus has been on the particle size distributions of the nanocomposite powder during the milling and on the surface morphology of the nanocomposite-compacted materials after compaction with and without relaxation assists. Experimental results for different milling systems are presented showing the effects of milling time and material ratio. It was found that a longer mixing time give a higher degree of dispersion of the nanopowder on the PMMA particle surfaces. Furthermore, with increasing content of NiFe2O4 nanopowder, the reduction of the particle size was more effective. Different postcompacting profiles, i.e. different energy distributions between the upper and lower parts of the compacted powder bed, lead to different movements of the various particles and particle layers. Uniformity, homogeneity, and densification on the surfaces in the compacted powder are influenced by the postcompacting magnitude and direction. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by reducing the expansion of the compacted volume and by reducing the different opposite velocities, giving the compacted composite bed a more homogeneous opposite velocity during the decompacting stage and reducing the delay time between the successive pressure waves.

  • 4. Ferrero, B.
    et al.
    Boronat, T.
    Moriana, Rosana
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Fenollar, O.
    Balart, R.
    Green composites based on wheat gluten matrix and posidonia oceanica waste fibers as reinforcements2013In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 34, no 10, p. 1663-1669Article in journal (Refereed)
    Abstract [en]

    In this work, green composites from renewable resources were manufactured and characterized. A fibrous material derived from Posidonia oceanica wastes with high cellulose content (close to 90 wt% of the total organic component) was used as reinforcing material. The polymeric matrix to bind the fibers was a protein (wheat gluten) type material. Composites were made by hot-press molding by varying the gluten content on composites in the 10-40 wt% range. Mechanical properties were evaluated by standardized flexural tests. Thermo-mechanical behavior of composites was evaluated with dynamic mechanical analysis (torsion DMA) and determination of heat deflection temperature. Morphology of samples was studied by scanning electronic microscopy and the water uptake in terms of the water submerged time was evaluated to determine the maximum water uptake of the fibers in the composites. Composites with 10-40 wt% gluten show interesting mechanical performance, similar or even higher to many commodity and technical plastics, such as polypropylene. Water resistance of these composites increases with the amount of gluten. Therefore, the sensitiveness to the water of the composites can be tailored with the amount of gluten in their formulation.

  • 5.
    Hallander, Per
    et al.
    SAAB AB, Linkoping, Sweden..
    Sjölander, Jens
    SAAB AB, Linkoping, Sweden..
    Petersson, Mikael
    SAAB AB, Linkoping, Sweden..
    Andersson, Tomas
    SAAB AB, Linkoping, Sweden..
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Fast forming of multistacked UD prepreg using a high-pressure process2019In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 40, no 9, p. 3550-3561Article in journal (Refereed)
    Abstract [en]

    In this article, the opportunities of fast forming of multistacked UD prepreg when using high-pressure forming were examined in an experimental study. Forming is often considered a bottleneck in manufacturing of composite aircraft parts and speeding up the process is, therefore, of great interest. A Quintus Flexform fluid cell press was used to create pressure of 100 to 400 bars. In the study, different lay-up sequences and thicknesses were tested for manufacturing of c-shaped coupons. Tests were performed at different temperatures and some of the samples were sandwiched with mild steel sheets referred to as a steel sheet dummy. A case study was also performed on a double-curved spar geometry. It was found that forming at a relatively high overall pressure level combined with an elevated temperature, created squeeze flow-related wrinkle formations, and radius thinning. With high pressure forming, material compression/compaction mechanisms showed to have great influence on the forming result. This differs to low pressure vacuum forming, where intraply shear, interply shear, and ply bending are the dominant forming mechanisms. The steel sheet dummy minimized the squeeze flow related wrinkle in the web and flanges. Instead the forming temperature was found to exert the greatest influence on radius thinning. When forming at room temperature, radius thinning was almost eliminated and instead bending-related wrinkles in the flange below the radii appeared. POLYM. COMPOS., 40:3550-3561, 2019.

  • 6.
    Hallander, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Sjölander, Jens
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Forming of composite spars including interlayers of aligned, multiwall, carbon nanotubes: an experimental study2016In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569Article in journal (Refereed)
    Abstract [en]

    Carbon nanotubes offer the potential for improved or changed matrix properties, thereby enabling the creation of novel, multifunctional composite materials. By using highly-aligned, multiwall, carbon nanotubes (MWCNT) with thermoset resins, good dispersion and distribution of nanotubes is obtained. To date, research has mainly focused on improving the growth process of the aligned MWCNTs, however little has been done on the processing of composites that include MWCNTs as interlayers in the stack.  The aim of this work is to study how the aligned MWCNTs are affected within composite part forming. The study shows that MWCNTs are influenced by the shearing that occurs during forming, but still maintain their integrity. To some extent, the shear pattern observed in the MWCNTs after deformation provides an indication of deformation modes. However, the presence of MWCNTs also significantly influences the forming characteristics of the prepreg stack.

  • 7.
    Kupka, Vojtech
    et al.
    Brno Univ Technol, CEITEC Cent European Inst Technol, Brno 61200, Czech Republic..
    Zhou, Qi
    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), Fibre- and Polymer Technology.
    Tang, Hu
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH). Royal Inst Technol KTH, AlbaNova Univ Ctr, Sch Biotechnol, S-10691 Stockholm, Sweden..
    Slouf, Miroslav
    Acad Sci Czech Republ, Inst Macromol Chem, CR-16206 Prague, Czech Republic..
    Vojtova, Lucy
    Brno Univ Technol, CEITEC Cent European Inst Technol, Brno 61200, Czech Republic.;SCITEG As, U Vodarny 2965-2, Brno 61600, Czech Republic..
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Jancar, Josef
    Brno Univ Technol, CEITEC Cent European Inst Technol, Brno 61200, Czech Republic.;SCITEG As, U Vodarny 2965-2, Brno 61600, Czech Republic..
    Well-dispersed polyurethane/cellulose nanocrystal nanocomposites synthesized by a solvent-free procedure in bulk2019In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 40, p. E456-E465Article in journal (Refereed)
    Abstract [en]

    Polyurethane (PU) nanocomposites utilizing cellulose nanocrystals (CNCs) as nanofiller and amorphous PU matrix were synthesized in a novel solvent-free bulk process. A green nanofiller, CNCs, was studied as reinforcement and was further modified by grafting poly(ethylene glycol) (PEG) on the CNC surface (CNC-PEG). Transmission electron microscopy revealed an excellent dispersion of the PEGylated CNC nanoparticles in the PU matrix, whereas as-received CNCs formed agglomerates. The results indicated strong improvements in tensile properties with Young's modulus increasing up to 50% and strength up to 25% for both, PU/CNC and PU/CNC-PEG nanocomposites. The enhanced tensile modulus was attributed to stiff particle reinforcement together with an increase in glass transition temperature.

  • 8. Moriana, Rosana
    et al.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ribes-Greus, Amparo
    Assessing the Influence of Cotton Fibers on the Degradation in Soil of a Thermoplastic Starch-Based Biopolymer2010In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 31, no 12, p. 2102-2111Article in journal (Refereed)
    Abstract [en]

    Biocomposites consisting of cotton fibers and a commercial starch-based thermoplastic were subjected to accelerated soil burial test. Fourier transform infrared (FTIR) spectrometry analysis was carried out to provide chemical structural information of the polymeric matrix and its reinforced biocomposites. The effects that take place as a consequence of the degradation in soil of both materials were studied by FTIR-ATR, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). When the polymeric matrix and the reinforced biocomposite are submitted to soil burial test, the infrared studies display a decrease in the C=O band associated to the ester group of the synthetic component as a consequence of its degradation. The crystalline index of both materials decreased as a function of the degradation process, where the crystalline structure of the reinforced biocomposite was the most affected. In accordance, the degraded reinforced biocomposite micrographs displayed a more damaged morphology and fracture surface than the degraded polymeric matrix micrographs. On the other hand, the same thermal decomposition regions were assessed for both materials, regardless of the degradation time. Kissinger, Criado, and Coats-Redfern methods were applied to analyze the thermogravimetric results. The kinetic triplet of each thermal decomposition process was determined for monitoring the degradation test. The thermal study confirms that starch was the most biodegradable polymeric matrix component in soil. However, the presence of cotton fiber modified the degradation rate of both matrix components; the degradability in soil of the synthetic component was slightly enhanced, whereas the biodegradation rate of the starch slowed down as a function of the soil exposure time. POLYM. COMPOS., 31:2102-2111, 2010.

  • 9.
    Mårtensson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Volvo Car Group, Sweden.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Cost and weight efficient partitioning of composite automotive structures2015In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569Article in journal (Refereed)
    Abstract [en]

    To make carbon fiber composites not only weight but also cost effective in high volume production the different cost drivers need to be addressed and new design philosophies considered. This study analyzes integral and differential design approaches when partitioning large complex composite structures. The influence of different partition philosophies are investigated based on a framework of composites manufacturing cost modelling and structural optimization and the effects are exemplified by a case study. The results show that depending on how the partitioning is made the structural performance and the manufacturing cost is affected. More particularly, if the partitioning is made with the most beneficial philosophy differential designs can improve both these important parameters.

  • 10.
    Vilela, Carla
    et al.
    Department of Chemistry, CICECO – Aveiro Institute of Materials, University of Aveiro, Aveiro 3810-193, Portugal.
    Engström, Joakim
    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, Coating Technology.
    Valente, Bruno F. A.
    Department of Chemistry, CICECO – Aveiro Institute of Materials, University of Aveiro, Aveiro 3810-193, Portugal.
    Jawerth, Marcus
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Carlmark, Anna
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology.
    Freire, Carmen S. R.
    Department of Chemistry, CICECO – Aveiro Institute of Materials, University of Aveiro, Aveiro 3810-193, Portugal.
    Exploiting poly(ɛ-caprolactone) and cellulose nanofibrils modified with latex nanoparticles for the development of biodegradable nanocomposites2018In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569Article in journal (Refereed)
    Abstract [en]

    This study reports the development of nanocomposites based on poly(?-caprolactone) (PCL) and cellulose nanofibrils (CNF) modified with cationic latex nanoparticles. The physical adsorption of these water-based latexes on the surface of CNF was studied as an environment-friendly strategy to enhance the compatibility of CNF with a hydrophobic polymeric matrix. The latexes are composed of amphiphilic block copolymers based on cationic poly(N,N-dimethylaminoethyl methacrylate-co-methacrylic acid) as the hydrophilic block, and either poly(methyl methacrylate) or poly(n-butyl methacrylate) as the hydrophobic block. The simple and practical melt-mixing of PCL- and latex-modified CNF yielded white homogeneous nanocomposites with complete embedment of the nanofibrils in the thermoplastic matrix. All nanocomposites are semicrystalline materials with good mechanical properties (Young's modulus?=?43.6?52.3 MPa) and thermal stability up to 335?340°C. Degradation tests clearly showed that the nanocomposites slowly degrade in the presence of lipase-type enzyme. These PCL/CNF-latex nanocomposite materials show great promise as future environmentally friendly packaging materials. POLYM. COMPOS., 2018. ? 2018 Society of Plastics Engineers

  • 11.
    Åkermo, Malin
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Astrom, B. T.
    Modeling compression molding of all-thermoplastic honeycomb core sandwich components. Part A: Model development2000In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 21, no 2, p. 245-256Article in journal (Refereed)
    Abstract [en]

    The compression molding process is studied with the aim of modeling the instantaneous degree of face-core bonding in all-thermoplastic sandwich components during molding. The theory of bonding is briefly discussed and it is concluded that for most thermoplastic materials, processing is performed at temperatures where full bond strength is seemingly immediately established at positions in full face-core contact. A two-dimensional model is developed to predict increase in contact area due to flow of melted core material during molding. Further, heat transfer during processing is modeled in order to determine the extent of melted core material. The two models are coupled into one process model and a numerical example is presented illustrating the predicted behavior of polypropylene-based sandwich components in compression molding. The process model suggests that the face-core bond strength may be significantly increased through flow of the melted core wall.

  • 12.
    Åkermo, Malin
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Astrom, B. T.
    Modeling compression molding of all-thermoplastic honeycomb core sandwich components. Part B: Model verification2000In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 21, no 2, p. 257-267Article in journal (Refereed)
    Abstract [en]

    The compression molding process for manufacturing of all-thermoplastic honeycomb core sandwich components is studied with the aim of verifying a previously proposed model describing the instantaneous face-core bonding during molding. Experiments are performed with glass/polypropylene (PP) faces and PP honeycomb core and experimental data are compared to model predictions in terms of temperature and degree of face-core interfacial contact with reasonable good agreement. Model predictions show that the face-core interface bond strength may increase with up to 200% when molding at an interface temperature slightly above the crystal melting temperature of the matrix for only a few seconds. The influence of the major process parameters, including molding temperature, molding pressure and core viscosity, on the predicted bond strength is investigated using the model.

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