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Stiffness contribution of various wood fibers to composite materials
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
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.

Place, publisher, year, edition, pages
2006. Vol. 40, no 8, 663-699 p.
Keyword [en]
wood fiber composites, elastic properties, micromechanics, stiffness characterization
National Category
Wood Science Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6097DOI: 10.1177/0021998305055276ISI: 000237196900001Scopus ID: 2-s2.0-33645744206OAI: oai:DiVA.org:kth-6097DiVA: diva2:10711
Note
QC 20100914Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2010-09-14Bibliographically approved
In thesis
1. Hygroelastic behaviour of wood-fibre based materials on the composite, fibre and ultrastructural level
Open this publication in new window or tab >>Hygroelastic behaviour of wood-fibre based materials on the composite, fibre and ultrastructural level
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Wood fibres can 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 wood fibres for composite materials. The long-term aim is to design engineered wood fibre composites based on better basic knowledge of wood fibres.

Mechanistic models have been used to link the fibrous microstructure with macroscopic composite engineering properties. The properties have been characterized 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 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, illustrating how the mixed experimental-modelling approaches can be used in more efficient materials screening and selection.

An improved micromechanical analysis for wood-fibre composites has been presented. The model is more appropriate to combine with laminate analogy, to link fibre properties on the microscale to the macroscopic composite properties and vice versa. It also offers the possibility to include the effects of ultrastructure since it can account for an arbitrary number of phases. An approach to model ultrastructure-fibre property relations has been demonstrated. It includes analytical modelling of multilayered cylindrical fibres as well as finite element modelling of fibres with irregular geometry characterized with microscopy. Both approaches are useful and could be combined with experiments to reveal insights that can pave way for a firmer link between the wood fibre ultrastructure and wood fibre properties.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xiii, 31 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0414
Keyword
wood fibres, ultrastructure, structure-property relations, microfibril angle, composites, characterization methods, hygroelastic properties, micromechanics, modelling, reinforcement potential
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-4098 (URN)
Public defence
2006-09-29, E2, Lindstedsvägen 3, Stockholm, 10:00
Opponent
Supervisors
Note

QC 20100914

Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2013-01-14Bibliographically approved
2. Hygroelastic properties of wood fibres for composite applications
Open this publication in new window or tab >>Hygroelastic properties of wood fibres for composite applications
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:nbn:se:kth:diva-479 (URN)
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

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