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Dynamic-mechanical properties of wood-fibre reinforced polyactide: experimental characterization and micro-mechanical modelling
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
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2006 (English)In: Journal of Thermoplastic Composite Materials, ISSN 0892-7057, E-ISSN 1530-7980, Vol. 19, no 6, 613-638 p.Article in journal (Refereed) Published
Abstract [en]

Wood-fiber reinforced polylactide is a biodegradable compositewhere both fibers and matrix are from renewableresources. When designing new materials of this kind, itis useful to measure the influence of fiber–matrixinterface properties on macroscopic mechanicalproperties. In particular, a quantitative measure of thedynamic stress transfer between the fibers andthe matrix when the material is subjected tocyclic loading would simplify the development of wood-fibercomposites. This is obtained by comparing themechanical dissipation of the composite with avalue predicted by a viscoelastic micromechanical model basedon perfect interfacial stress transfer. Theloss factors predicted by the model are 0.12 and 0.16 at dryand humid conditions, respectively, which amountto 63 and 66% of the experimentally determinedvalues. For Young's moduli the predicted values are 1.01 and0.88 GPa, which correspond to 92% of the experimentallydetermined values. The mismatch between thepredicted and experimental values may be attributed toimperfect interfaces with restrained stress transfer.Loss factors are also determined for specificmolecular bonds using dynamic Fourier transform infrared(FT-IR) spectroscopy. These values show the sametrends with regard to moisture content as themacroscopically determined loss factors.

Place, publisher, year, edition, pages
2006. Vol. 19, no 6, 613-638 p.
Keyword [en]
polylactide • wood fibers • micromechanics • stress transfer • imperfect interfaces • dynamic FT–IR
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6991DOI: 10.1177/0892705706067480ISI: 000241384300001Scopus ID: 2-s2.0-33750180040OAI: oai:DiVA.org:kth-6991DiVA: diva2:11861
Note
QC 20100714Available from: 2007-04-19 Created: 2007-04-19 Last updated: 2011-07-13Bibliographically approved
In thesis
1. Stress-transfer mechanisms in wood-fibre composites
Open this publication in new window or tab >>Stress-transfer mechanisms in wood-fibre composites
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 12 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0433
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-4338 (URN)
Presentation
2007-04-17, Sal D2, KTH, Lindstedtsvägen 5, Stockholm, 13:15
Opponent
Supervisors
Note

QC 20101102

Available from: 2007-04-19 Created: 2007-04-19 Last updated: 2013-01-15Bibliographically approved
2. Wood-fibre composites: Stress transfer and hygroexpansion
Open this publication in new window or tab >>Wood-fibre composites: Stress transfer and hygroexpansion
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wood fibres is a type of natural fibres suitable for composite applications. The abundance of wood in Swedish forests makes wood-fibre composites a new and interesting application for the Swedish pulp and paper industry. For large scale production of composites reinforced by wood fibres to be realized, the mechanical properties of the materials have to be optimized. Furthermore, the negative effects of moisture, such as softening, creep and degradation, have to be limited. A better understanding of how design parameters such as choice of fibres and matrix material, fibre modifications and fibre orientation distribution affect the properties of the resulting composite material would help the development of wood-fibre composites.

In this thesis, focus has been on the fibre-matrix interface, wood-fibre hygroexpansion and resulting mechanical properties of the composite. The importance of an efficient fibre-matrix interface for composite properties is well known, but the determination of interface properties in wood-fibre composites is difficult due to the miniscule dimensions of the fibres. This is a problem also when hygroexpansion of wood fibres is investigated. Instead of tedious single-fibre tests, more straightforward, macroscopic approaches are suggested. Halpin-Tsai’s micromechanical models and laminate analogy were used to attain efficient interface characteristics of a wood-fibre composite. When Halpin-Tsai’s model was replaced by Hashin’s concentric cylinder assembly model, a value of an interface parameter could be derived from dynamic mechanical analysis. A micromechanical model developed by Hashin was used also to identify the coefficient of hygroexpansion of wood fibres. Measurements of thickness swelling of wood-fibre composites were performed. Back-calculation through laminate analogy and the micromechanical model made it possible to estimate the wood-fibre coefficient of hygroexpansion. Through these back-calculation procedures, information of fibre and interface properties can be gained for ranking of e.g. fibre types and modifications.

Dynamic FT-IR (Fourier Transform Infrared) spectroscopy was investigated as a tool for interface characterization at the molecular level. The effects of relative humidity in the test chamber on the IR spectra were studied. The elastic response of the matrix material increased relative to the motion of the reinforcing cellulose backbone. This could be understood as a stress transfer from fibres to matrix when moisture was introduced to the system, e.g. as a consequence of reduced interface efficiency in the moist environment. The method is still qualitative and further development is potentially very useful to measure stress redistribution on the molecular level.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 51 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2010:9
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-12309 (URN)
Public defence
2010-04-16, K1, Teknikringen 56 entrépla, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC20100714Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2010-11-02Bibliographically approved

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