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Effects of Moisture on Dynamic Mechanical Properties of Wood Fiber Composites Studied by Dynamic FT-IR Spectroscopy
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2008 (English)In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 27, no 16-17, 1709-1721 p.Article in journal (Refereed) Published
Abstract [en]

Wood fiber reinforced polylactide is a biodegradable composite where both fibers and matrix are from renewable resources. In the development of such new materials, information on mechanical behavior on the macroscopic and the molecular level is useful. In this study, dynamic Fourier transform infrared (FT-IR) spectroscopy is used to measure losses at the molecular level during cyclic tensile loading for bonds that are characteristic of the cellulosic fibers and the polylactid matrix. This molecular behavior is compared with measured macroscopic hysteresis losses for different moisture levels. The results show that moisture ingress will transfer the load from the fibers to the matrix, and that a more efficient fiber-matrix interface would diminish mechanical losses. Although the dynamic FT-IR spectroscopy method is still qualitative, this investigation shows that it can provide information on the stress transfer of the constituents in wood fiber reinforced plastics.

Place, publisher, year, edition, pages
2008. Vol. 27, no 16-17, 1709-1721 p.
Keyword [en]
wood fiber, dynamic FT-IR, stress transfer, moisture, interface
National Category
Paper, Pulp and Fiber Technology Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6992DOI: 10.1177/0731684407084663ISI: 000260411900005OAI: oai:DiVA.org:kth-6992DiVA: diva2:11862
Note
QC20100714. Tidigare titel "Effects of moisture on dynamic mechanical properties of wood-fibre reinforced polylactide studied by dynamic FT-IR spectroscopy. Available from: 2007-04-19 Created: 2007-04-19 Last updated: 2010-11-02Bibliographically 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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Almgren, Karin M.Åkerholm, MargarethaGamstedt, Kristofer
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