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Role of fibre-fibre and fibre-matrix adhesion in stress transfer in composites made from resin-impregnated paper sheets.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
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2009 (English)In: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 29, no 5, 551-557 p.Article in journal (Refereed) Published
Abstract [en]

Paper-reinforced plastics are gaining increased interest as packaging materials, where mechanical properties are of great importance. Strength and stress transfer in paper sheets are controlled by fibre-fibre bonds. In paper-reinforced plastics, where the sheet is impregnated with a polymer resin, other stress-transfer mechanisms may be more important. The influence of fibre-fibre bonds on the strength of paper-reinforced plastics was therefore investigated. Paper sheets with different degrees of fibre-fibre bonding were manufactured and used as reinforcement in a polymeric matrix. Image analysis tools were used to verify that the difference in the degree of fibre-fibre bonding had been preserved in the composite materials. Strength and stiffness of the composites were experimentally determined and showed no correlation to the degree of fibre-fibre bonding, in contrast to the behaviour of unimpregnated paper sheets. The degree of fibre-fibre bonding is therefore believed to have little importance in this type of material, where stress is mainly transferred through the fibre-matrix interface.

Place, publisher, year, edition, pages
2009. Vol. 29, no 5, 551-557 p.
Keyword [en]
Composites, Wood, Microscopy
National Category
Mechanical Engineering Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-6993DOI: 10.1016/j.ijadhadh.2008.11.002ISI: 000265185300011Scopus ID: 2-s2.0-62249147592OAI: oai:DiVA.org:kth-6993DiVA: diva2:11863
Note
Tidigare titel: Comparison of stress-transfer mechanisms in paper sheets and composites med from resin-impregnated sheets. Uppdaterad från submitted till published: 20101102. QC 20101102Available 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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