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Moisture uptake and hygroexpansion of wood fiber composite materials with polylactide and polypropylene matrix materials
Innventia.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
Innventia.
Innventia.
2009 (English)In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 30, no 12, 1809-1816 p.Article in journal (Refereed) Published
Abstract [en]

Effects of butantetracarboxylic acid (BTCA) modification, choice of matrix, and fiber volume fraction on hygroexpansion of wood fiber composites have been investigated. Untreated reference wood fibers and BTCA-modified fibers were used as reinforcement in composites with matrices composed of polylactic acid (PLA), polypropylene (PP), or a mixture thereof. The crosslinking BTCA modification reduced the out-of-plane hygroexpansion of PLA and PLA/PP composites, under water-immersed and humid conditions, whereas the swelling increased when PP was used as matrix material. This is explained by difficulties for the BTCA-modified fibers to adhere to the PP matrix. Fiber volume fraction was the most important parameter as regards out-of-plane hygroexpansion, with a high-fiber fraction leading to large hygroexpansion. Fiber-matrix wettability during processing and consolidation also showed to have a large impact on the dimensional stability and moisture uptake. POLYM. COMPOS., 30:1809-1816, 2009.

Place, publisher, year, edition, pages
2009. Vol. 30, no 12, 1809-1816 p.
Keyword [en]
DIMENSIONAL STABILITY; MECHANICAL-PROPERTIES; ABSORPTION; POLYMER; DEGRADATION; WATER; ACID
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-12288DOI: 10.1002/pc.20753ISI: 000272284900010Scopus ID: 2-s2.0-73249147817OAI: oai:DiVA.org:kth-12288DiVA: diva2:307604
Note
QC 20100617Available from: 2010-04-01 Created: 2010-04-01 Last updated: 2017-12-12Bibliographically 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.
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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