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  • 51.
    Tanpichai, Supachok
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Cross-linked nanocomposite hydrogels based on cellulose nanocrystals and PVA: Mechanical properties and creep recovery2016Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 88, s. 226-233Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cellulose nanocrystal (CNC) reinforced poly(vinyl alcohol) (PVA) hydrogels with a water content of ∼92% were successfully prepared with glutaraldehyde (GA) as a cross-linker. The effects of the CNC content on the thermal stability, swelling ratio and mechanical and viscoelastic properties of the cross-linked hydrogels were investigated. The compressive strength at 60% strain for the hydrogels with 1 wt% CNCs increased by 303%, from 17.5 kPa to 53 kPa. The creep results showed that the addition of CNCs decreased the creep elasticity due to molecular chain restriction. The almost complete strain recovery (∼97%) after fixed load removal for 15 min was observed from the hydrogels with CNCs, compared with 92% strain recovery of the neat cross-linked PVA hydrogels. The incorporation of CNCs did not affect the swelling ratio and thermal stability of the hydrogels. These results suggest the cross-linked CNC-PVA hydrogels have potential for use in biomedical and tissue engineering applications.

  • 52.
    Tanpichai, Supachok
    et al.
    Learning Institute, King Mongkut's University of Technology Thonburi.
    Sampson, William W.
    School of Materials, University of Manchester.
    Eichhorn, Stephen J.
    College of Engineering, Mathematics and Physical Sciences, University of Exeter.
    Stress transfer in microfibrillated cellulose reinforced poly(vinyl alcohol) composites2014Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 65, s. 186-191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Combined homogenisation and sonication treatments of micron-sized lyocell fibres were used to generate microfibrillated cellulose (MFC) with fibril diameters of ∼350 nm. No further reduction in fibril diameter was observed after 30 min treatment. Poly(vinyl alcohol) (PVA) composites reinforced with these fibrils were fabricated using solvent casting and physical and mechanical properties were investigated. The presence of MFC in PVA increased the thermal degradation of the polymer. An increase in both the tensile strength and modulus of the composites was observed for up to 3 wt.% of fibrils; beyond this point no significant increases were observed. An estimate of ∼39 GPa is made for the fibril modulus based on this increase. Stress-transfer between the polymer resin and the fibrils was investigated using Raman spectroscopy. Stress transfer in the composite is shown to be greater than that of a pure network of fibres, indicating a good fibre-matrix bond

  • 53.
    Tanpichai, Supachok
    et al.
    School of Materials, University of Manchester.
    Sampson, William W.
    School of Materials, University of Manchester.
    Eichhorn, Stephen J.
    College of Engineering, Mathematics and Physical Sciences, University of Exeter.
    Stress-transfer in microfibrillated cellulose reinforced poly(lactic acid) composites using Raman spectroscopy2012Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 43, nr 7, s. 1145-1152Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lyocell fibres were used to make microfibrillated cellulose (MFC) by combined homogenisation and sonication. A web-like structure was obtained with fibril diameters in the range of several micrometers to less than 80 nm. Composite samples with PLA resin reinforced with MFC networks were prepared using compression moulding. Young's modulus and tensile strength of these composites increased by ∼60% and 14% respectively, compared to the pure resin material. Raman spectroscopy was used to monitor the molecular deformation of networks and composite materials. A Raman band initially located at ∼1095 cm -1 was observed to shift towards a lower wavenumber position upon tensile deformation. The rate of Raman band shift with respect to strain for the composites was higher than for the pure MFC networks, indicating that the observed improvement in mechanical properties results from stress transfer from the PLA resin to the MFC fibrils.

  • 54.
    Vargas, Natalia Herrera
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Salaberria, Aiser M.
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Polytechnic School, University of the Basque Country.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Plasticized polylactic acid nanocomposite films with cellulose and chitin nanocrystals prepared using extrusion and compression molding with two cooling rates: effects on mechanical, thermal and optical properties2016Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 83, s. 89-97Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Triacetate citrate plasticized poly lactic acid and its nanocomposites based on cellulose nanocrystals (CNC) and chitin nanocrystals (ChNC) were prepared using a twin-screw extruder. The materials were compression molded to films using two different cooling rates. The cooling rates and the addition of nanocrystals (1 wt%) had an impact on the crystallinity as well as the optical, thermal and mechanical properties of the films. The fast cooling resulted in more amorphous materials, increased transparency and elongation to break, (approx. 300%) when compared with slow cooling. Chitin nanocomposites were more transparent than cellulose nanocomposites; however, microscopy study showed presence of agglomerations in both materials. The mechanical properties of the plasticized PLA were improved with the addition of a small amount of nanocrystals resulting in PLA nanocomposites, which will be further evaluated for film blowing and thus packaging applications.

  • 55.
    Varna, Janis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Berglund, Lars A.
    Luleå tekniska universitet.
    Ericson, M.L.
    Transverse single-fibre test for interfacial debonding in composites: 2. Modelling1997Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 28, nr 4, s. 317-326Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method was developed for determination of interfacial toughness parameters from a new transverse single-fibre test. In previous work, experimental procedures were developed. Interfacial debond growth in the arc and fibre direction was measured for transparent matrix polymer composites. In the present study, an earlier stress analysis by Toya was modified and combined with a critical energy release rate criterion, taking mode mixity effects into account. The developed model was used to determine interfacial toughness parameters. The model was able to describe and explain the main experimental observations of the debonding process. Treatment of the contact problem present for large debond angles is of interest for future work

  • 56.
    Wysocki, Maciej
    et al.
    SICOMP AB, Swedish Institute of Composites.
    Toll, Staffan
    Royal Institute of Technology, Stockholm.
    Larsson, Ragnar
    Chalmers University of Technology.
    Asp, Leif
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Anisotropic and tension-compression asymmetric model for composites consolidation2010Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 41, nr 2, s. 284-294Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A constitutive model for anisotropic and tension-compression asymmetric response of a fibrous preform is developed and solved using a FE software. Applicability of the method to complex geometries is demonstrated by analysis the consolidation of an axisymmetric filament wound pressure vessel made from commingled yarns. Three different winding patterns are considered. In conclusions, the consolidation of the whole vessel, except at the opening, is prevented by the loading mode where the pressure is applied on the interior. To succeed in manufacturing of this type of pressure vessel, use of an oversized preform that allows extension in the fibre direction is suggested. The proposed model provides precisely the required spatial distribution of fibre excess for consolidation without fibre tension: on average a 2 % oversize for both winding patterns.

  • 57.
    Zhang, H.
    et al.
    Luleå tekniska universitet.
    Ericson, M.L.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Berglund, Lars A.
    Luleå tekniska universitet.
    Transverse single-fibre test for interfacial debonding in composites: 1. Experimental observations1997Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 28, nr 4, s. 309-315Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Micromechanical methods for studies of interfacial debonding in fibre composites provide the possibility of comparing different materials. Since most previous composite studies focus on shear loading of the fibre matrix interface, the debonding process in single-fibre glass fibre/epoxy composites was studied in situ by optical microscopy during transverse tensile loading. Specimens had cylindrical debond cracks of known dimensions created in fragmentation tests. Mechanisms for debond growth were described for two materials where the difference was in glass fibre surface treatment. As the debonds reached a critical size in the arc (circumferential) direction, unstable debond growth occurred in the fibre direction. The debond angle at instability was fairly similar for both materials, although the material based on glass fibre treated with a coupling agent reached twice as high stress before instability.

  • 58.
    Zhou, Xiaojian
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sain, Mohini
    Centre for Biocomposites and Biomaterials Processing, University of Toronto, University of Toronto, Centre for Biocomposites and Biomaterials Processing, Faculty of Forestry, University of Toronto.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Semi-rigid biopolyurethane foams based on palm-oil polyol and reinforced with cellulose nanocrystals2016Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 83, s. 56-62Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, water-blown biopolyurethane (BPU) foams based on palm oil were developed and cellulose nanocrystals (CNC) were incorporated to improve the mechanical properties of the foams. In addition, the foams were compared with petroleum polyurethane (PPU) foam. The foam properties and cellular morphology were characterized. The obtained results revealed that a low-density, semi-rigid BPU foam was prepared using a new formulation. CNC as an additive significantly improved the compressive strength from 54 to 117 kPa. Additionally, cyclic compression tests indicated that the addition of CNC increased the rigidity, leading to decreased deformation resilience. The dimensional stability of BPU foams was increased with increasing CNC concentration for both heating and freezing conditions.Therefore, the developed BPU nanocomposite foams are expected to have great potential as core material in composite sandwich panels as well as in other construction materials.

  • 59.
    Zhuang, Linqi
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Texas A&M, College Station; University of Lorraine, France.
    Pupurs, Andrejs
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. SICOMP Swerea.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Talreja, Ramesh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Texas A&M University, College Station, TX .
    Ayadi, Zoubir
    University of Lorraine.
    Effects of Inter-Fiber Spacing on Fiber-matrix Debond Crack Growth in Unidirectional Composites under Transverse Loading2018Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 109, s. 463-471Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The energy release rate (ERR) of a fiber-matrix debond crack in a unidirectional composite subjected to transverse tension is studied numerically. The focus of the study is the effect of the proximity of the neighboring fibers on the ERR. For this, a hexagonal pattern of fibers in the composite cross-section is considered. Assuming one fiber to be debonded at certain initial debond arc-length, the effect of the closeness of the surrounding six fibers on the ERR of the crack is studied with the inter-fiber distance as a parameter. Using an embedded cell consisting of discrete fibers in a matrix surrounded by the homogenized composite, a finite element model and the virtual crack closure technique are used to calculate the ERR. Results show that the presence of the local fiber cluster accelerates the crack growth up to a certain initial crack angle, beyond which the opposite effect occurs. It is also found that the residual stress due to thermal cooldown reduces the ERR. However, the thermal cooldown is found to enhance the debond growth in plies within a cross-ply laminate.

  • 60.
    Zhuang, Linqi
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Texas A&M University, College Station, TX, USA.
    Talreja, Ramesh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Materials Science and Engineering, Texas A&M University, College Station, TX, USA. Department of Aerospace Engineering, Texas A&M University, College Station, TX, USA.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Transverse crack formation in unidirectional composites by linking of fibre/matrix debond cracks2018Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 107, s. 294-303Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plausible mechanisms of transverse crack formation in unidirectional (UD) composites under applied tension normal to fibres are investigated numerically using a finite element model. Two initial scenarios are considered: Scenario 1 where a pre-existing single fibre/matrix debond crack kinks out into the matrix and induces fibre/matrix debonding at neighbouring fibres, and Scenario 2 where multiple pre-existing debond cracks link up by the debond growth and crack kink-out process. The 2-D finite element model consists of a circular region of matrix with a central fibre surrounded by six fibres in a hexagonal pattern. The region is embedded in a homogenized UD composite of rectangular outer boundary. Energy release rates (ERRs) of interface cracks and kinked-out cracks are calculated under applied tension normal to fibres. Results show that Scenario 2 is more likely to lead to formation of a transverse crack than Scenario 1. These results provide understanding of the roles of fibre clustering and fibre volume fraction on transverse crack formation in composites

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