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Characterization of interfacial stress transfer ability by dynamic mechanical analysis of cellulose fiber based composite materials
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
2010 (English)In: Composite interfaces (Print), ISSN 0927-6440, E-ISSN 1568-5543, Vol. 17, no 9, 845-861 p.Article in journal (Refereed) Published
Abstract [en]

The stress transfer ability at the fiber-matrix interface of wood fiber composites is known to affect the mechanical properties of the composite. The evaluation of interface properties at the level of individual fibers is however difficult due to the small dimensions and variability of the fibers. The dynamical mechanical properties of composite and constituents, in this case wood fibers and polylactide matrix, was here used together with micromechanical modeling to quantify the stress transfer efficiency at the fiber-matrix interface. To illustrate the methodology, a parameter quantifying the degree of imperfection at the interface was identified by inverse modeling using a micromechanical viscoelastic general self-consistent model with an imperfect interface together with laminate analogy on the composite level. The effect of moisture was assessed by comparison with experimental data from dynamic mechanical analysis in dry and moist state. For the wood fiber reinforced polylactide, the model shows that moisture absorption led to softening and mechanical dissipation in the hydrophilic wood fibers and biothermoplastic matrix, rather than loss of interfacial stress transfer ability.

Place, publisher, year, edition, pages
2010. Vol. 17, no 9, 845-861 p.
Keyword [en]
Wood fibers, micromechanics, imperfect interface, inverse modeling, moisture
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-12285DOI: 10.1163/092764410X539235ISI: 000289243400003ScopusID: 2-s2.0-78649519331OAI: diva2:307602
Available from: 2010-04-01 Created: 2010-04-01 Last updated: 2011-09-08Bibliographically approved
In thesis
1. 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.
Trita-CHE-Report, ISSN 1654-1081 ; 2010:9
National Category
Paper, Pulp and Fiber Technology
urn:nbn:se:kth:diva-12309 (URN)
Public defence
2010-04-16, K1, Teknikringen 56 entrépla, KTH, Stockholm, 10:00 (English)
QC20100714Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2010-11-02Bibliographically approved

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Almgren, Karin M.Gamstedt, E. Kristofer
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