Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Hygroelastic properties of wood fibres for composite applications
KTH, Superseded Departments, Solid Mechanics.
2004 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Wood pulp fibres are gaining increased use for other applications than paper and board. Wood fibres can also be used as reinforcement in plastics for load carrying purposes. Some advantages compared with conventional man-made fibres are that wood fibres come from a renewable resource, have high specific stiffness and strength, are generally less hazardous to health, biodegradable, and can be manufactured at low cost and high volumes. A clear disadvantage with cellulose-based materials for structural use is their dimensional instability in humid environments.

The hygroelastic properties are of high importance in materials development of improved wood-fibre composites. This work deals with the stiffness and hygroexpansion of composite materials. Mechanistic models have been used to link the fibrous microstructure with these macroscopic engineering properties. The properties have been characterised experimentally for various wood-fibre composites and their fibre-mat preforms, by means of curvature measurements at various levels of relative humidity, as well as tensile and compressive tests. From these test results, the contribution of the fibres to the stiffness and hygroexpansion of composites were determined. These approaches can be used to rank different candidate fibres according to their potential as reinforcement in dimensionally stable and stiff composites. With straightforward macroscopic test methods and microstructural characterization, the longitudinal Young’s modulus and transverse coefficient of hygroexpansion of wood fibres were identified by inverse modelling. Some effects of various pulp processes and fibre modifications on the elastic properties of the fibre were observed, which illustrate how the mixed experimental-modelling approaches can be used in quantitative and more efficient materials development.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2004.
Series
Trita-HFL, ISSN 1104-6813 ; 0381
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-479OAI: oai:DiVA.org:kth-479DiVA: diva2:13970
Presentation
2004-12-16, Q2, 13:00 (English)
Opponent
Supervisors
Available from: 2004-11-08 Created: 2004-11-08 Last updated: 2012-03-22Bibliographically approved
List of papers
1. Influence of wood-fibre hygroexpansion on the dimensional instability of fibre mats and composites
Open this publication in new window or tab >>Influence of wood-fibre hygroexpansion on the dimensional instability of fibre mats and composites
2005 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, Vol. 36, no 6, 772-788 p.Article in journal (Refereed) Published
Abstract [en]

Wood fibres are gaining increased use as reinforcement in plastics. One of the disadvantages of cellulose-based fibres is their propensity to absorb water and swell. This inevitably leads to undesired dimensional instability of the composite and its fibre-mat preform. A measure of the hygroexpansion behaviour of the fibres could serve to rank the suitability of different kinds of cellulosic fibres with regard to dimensionally stable composites. A method has been developed to determine the hygroexpansion coefficient of wood fibres. Since fibre mats manufactured with conventional techniques generally have a thickness gradient of fibre orientation, fibre mats and composites will curl if the moisture content varies. Models based on laminate mechanics and micromechanics of hygroexpansion have been used to estimate the transverse hygroexpansion coefficient of the fibres from experimental results of curvature and thickness changes, and tensile stiffness of fibre mats based on unbleached sulphate cooked softwood. The fibre orientation distribution through the fibre-mat thickness was characterized with a tape-splitting technique and image analysis. The transverse hygroexpansion coefficient of the wood fibres was found to depend on the assumed ratios of the elastic parameters of the transversely isotropic fibres. Values in the range of 0.10-0.15 strain per relative change in moisture content were found for plausible degrees of elastic anisotropy of the fibres. Means of how to suppress dimensional instability of cellulose based composites and fibre mats are addressed.

Keyword
A. Fibres, A. Preform, A. Wood, C. Micro-mechanics, Hygroinstability
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6095 (URN)10.1016/j.compositesa.2004.10.023 (DOI)000229063300006 ()2-s2.0-15344347925 (Scopus ID)
Note
QC 20100920Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2010-09-20Bibliographically approved
2. Characterization methods for elastic properties of wood fibers from mats for composite materials
Open this publication in new window or tab >>Characterization methods for elastic properties of wood fibers from mats for composite materials
2006 (English)In: Wood and Fiber Science, ISSN 0735-6161, Vol. 38, no 1, 95-111 p.Article in journal (Refereed) Published
Abstract [en]

 Wood fibers offer excellent specific properties at low cost and are of interest as reinforcement in composites. This work compares two alternative test methods to determine the stiffness of wood fibers from simple macroscopic tests oil fiber mats. One method is compression of the fiber trial in the thickness direction, which uses a statistical micromechanical model based oil first-order beam theory to describe the deformation. The other method is tensile testing of fiber trials and back calculation of the fiber stiffness with I laminate model. Experiments include compression tests and tensile stiffness index tests as well as determination of fiber content, orientation, and dimensional distribution. For trials with unbleached softwood kraft fibers, all effective value of the Young's modulus of 20.1 GPa determined by the compression method call be compared with values of 17.4-19.0 GPa obtained from tensile tests. These are ill agreement with values for similar cellulosic fibers found in literature. The compression method is more appropriate for low-density fiber mats, while the tensile test works better for well-consolidated high-density fiber mats. The two methods have different ranges of applicability and are complementary to one another. Limitations of the methods are also discussed. The main advantage of the methods is that they are quantitative. The potential as stiffening reinforcement of various types of Fibers can be systematically investigated, even if the fiber mat microstructures are different.

Keyword
wood fiber, stiffness, fiber trial, test methods, composites
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6096 (URN)000235272600011 ()2-s2.0-33644673173 (Scopus ID)
Note
QC 20100902Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2010-09-02Bibliographically approved
3. Stiffness contribution of various wood fibers to composite materials
Open this publication in new window or tab >>Stiffness contribution of various wood fibers to composite materials
2006 (English)In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Journal of Composites Materials, Vol. 40, no 8, 663-699 p.Article in journal (Refereed) Published
Abstract [en]

Wood pulp fibers can serve as useful reinforcement of plastics for increased stiffness. To assess the potential of various wood fibers as reinforcement, a method has been developed to determine the contribution of the fibers to the elastic properties of the composite. A micromechanical composite model and classical laminate mechanics are used to relate the elastic properties of the fibers to the elastic properties of the composite. A large variety of composites made of various wood pulp fibers in an epoxy vinyl ester matrix was manufactured. From the tensile test results of the composites, the contributing Young's moduli of the fibers in the longitudinal direction are back-calculated and summarized. One finding is that there is an optimum in fiber stiffness as a function of lignin content. It is also found that industrially pulped hardwood fibers have higher stiffness than the corresponding softwood fibers. One example is kraft-cooked Norway spruce fiber, for which a Young's modulus of 40 GPa is found. The effects of hornification, prehydrolysis, and sulfite processing are also investigated. The results indicate that mild defibration process should be used, that does not damage the cell wall structure so that the inherent high stiffness of the native fibers can be retained. It can be concluded that the proposed method works well to rank the wood fiber candidates in terms of their contribution to the composite stiffness.

Keyword
wood fiber composites, elastic properties, micromechanics, stiffness characterization
National Category
Wood Science Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6097 (URN)10.1177/0021998305055276 (DOI)000237196900001 ()2-s2.0-33645744206 (Scopus ID)
Note
QC 20100914Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2010-09-14Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Neagu, Cristian
By organisation
Solid Mechanics
Mechanical Engineering

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 430 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf