workshop on single fiber testing and modeling - tu...

Workshop on

Single Fiber Testing and Modeling

Innventia AB, Stockholm, Sweden, 4-5 November, 2009

Book of Abstract

Co-hosted by: The Paper Mechanics Cluster and COST Action FP0802

Paper Mechanics Cluster and COST Action FP0802

Workshop on Single Fiber Testing and Modeling

Foreword The objective of the workshop on Single-Fibre Testing and Modeling is to collect knowledge and identify the state-of-the-art and future research directions in micromechanical testing and modeling of wood and pulp fibers as well as other natural fibres.

The first part of the workshop will be dedicated to presentations from invited distinguished scientists and poster presentations of ongoing or recently finished research activities related to the topic of the workshop. This Book of Abstracts summarises the abstracts of all contributions to the first part of the workshop.

The second part of the workshop will be reserved for discussions on the current state of research and the need for future research related to micromechanical testing and modeling of wood and pulp fibres.

The workshop is organised by COST Action FP0802, chaired by Karin Hofstetter at Vienna University of Technology, Austria, together with the Paper Mechanics Cluster within the Innventia Research Program 2009-2011, managed by Petri Mäkelä at Innventia AB, Stockholm. Sweden.

The program committee is composed of:

Karin Hofstetter (Vienna University of Technology, Austria) Lennart Salmén (Innventia AB, Stockholm Sweden) Lisbeth Thygesen (Forest & Landscape Denmark, University of Copenhagen) Michaela Eder (Max-Planck-Institute for Colloids and Interfaces, Potsdam, Germany) Kristofer Gamstedt (Royal Institute of Technology (KTH), Stockholm, Sweden) Petri Mäkelä (Innventia AB, Stockholm, Sweden)

The local organizers of the workshop are Petri Mäkelä, Lennart Salmén and Veronica Sundling at Innventia AB, Stockholm, Sweden.

The organisers express their gratitude to the financial support from the member companies of the Paper Mechanics Cluster and COST.



Table of contents Page

List of Participants.......................................................................................................................1

Workshop program ......................................................................................................................5

Abstracts – Invited lectures ........................................................................................................7

Multimodal testing of single fibers .....................................................................................9 S. M. Shaler

Exploring structure and deformation mechanisms of plant fibres ...............................10 M. Eder and I. Burgert

An interdisciplinary view on the strength of a fiber – fiber bond in paper...................12 E. Gilli, F. J. Schmied, C. Teichert, U. Hirn , L. Kappel , W. Bauer and R. Schennach

Wetting and tensile deformation of single spruce wood fibres followed by Raman microscopy ............................................................................................................14 N. Gierlinger, M. Eder and I. Burgert

Tensile strength of single fibers: test methods and data analysis ...............................16 J. Andersons

Fracture mechanisms observed during tensile testing of single fibres.......................17 J. Hornatowska

Micromechanics of single wood fiber; testing and modeling........................................18 P. Navi and M. Sedighi-Gilani

Mechanical testing of spider silk ......................................................................................19 B. Madsen

Single fibre testing – relation to variability......................................................................20 L. Salmén

Constitutive modeling of soft biological tissues with emphasis on the vasculature..........................................................................................................................21 T. C. Gasser

Finite Element Modelling of Tensile Tests of Geometrically Well-Characterized Single Wood Fibres ............................................................................................................22 E. K. Gamstedt

Abstracts – Poster sessions .....................................................................................................23

Tensile strength of bundles of softwood fibres ..............................................................25 L. S. Beltran and E. Schlangen

Characteristic and performance of elementary hemp fibres .........................................26 D. Dai and M. Fan



Measuring the bonded area of individual fiber-fiber bonds.......................................... 27 L. Kappel, U. Hirn, W. Bauer and R. Schennach

Three dimensional single fibre imaging in micro- and nano-scales ............................ 28 V. Koivu, T. Turpeinen, M. Myllys, J. Timonen and M. Kataja

An automated method to recognize individual fibers from three-dimensional tomographic images.......................................................................................................... 29 A. Miettinen, V. Koivu, T. Turpeinen, J. Timonen and M. Kataja

Modelling the hygroexpansion of normal and compression wood tracheids............. 30 R. C. Neagu, E. K. Gamstedt and S. L. Bardage

Fibre morphology – important for mechanosorptive creep .......................................... 31 A.-M. Olsson and L. Salmén

Production and characterization of wood fibres with defined properties for their use as reinforcing fibres in wood-polypropylene-composites ............................ 32 A. Pfriem, M. Zauer and M. Horbens

Variability and relation of lignin, low molecular mass phenolics and cell wall bound peroxidases in the needels of Serbian spruce (Picea omorika (Pančić) Purkynĕ) during four seasons.......................................................................................... 33 J. B. Pristov, A. Mitrović, V. Maksimović, D. Djikanović, D. Mutavdžić, J. Simonović and K. Radotić

Cell wall structural differences between hardwood and softwood studied by FT-IR, Raman and fluoresence spectroscopy ................................................................ 34 K. Radotić, D. Djikanović, J. Simonović, J. B. Pristov, A. Kalauzi, D. Bajuk-Bogdanović and M. Jeremić

Flexibility measurement of individual paper fibers using microrobotics.................... 35 P. Saketi, M. v. Essen and P. Kallio

Fibre strength, stiffness and thickness of Swedish grown hemp – a study of plant development and fibre conditions ......................................................................... 36 B. Svennerstedt, T. Nilsson and P.J. Gustafsson

Measuring fiber strength, using a single fiber fragmentation ...................................... 37 F. Thuvander and C. H. Ljungkvist

Analysis of strength of flax fibre bundles....................................................................... 38 A. Thygesen, B. Madsen, A. B. Thomsen and H. Lilholt

A developing in-situ inspection method on microstructure characteristics of wood deformation under loading..................................................................................... 39 Y. Yin, M. Bian, B. Liu and X. Jiang



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List of Participants

Name Company E-mail

Johan Alfthan Innventia AB [email protected]

Janis Andersons University of Latvia [email protected]

Rasmus Andersson Innventia AB [email protected]

Toni Antikainen TKK [email protected]

Dave Auty University of Aberdeen dave.auty@forestry/gsi.gov.uk

Thomas K Bader Vienna University of Technology [email protected]

Antanas Baltrusaitis Kaunas University of Technology [email protected]

Stig L. Bardage SLU [email protected]

Wolfgang Bauer Graz University of Technology [email protected]

Lupita Sierra Beltran Delft University of Technology [email protected]

Fredrik Berthold Innventia AB [email protected]

Ingela Bjurhager Royal Institute of Technology (KTH) [email protected]

Frank a Campo Stora Enso Research

Mönchengladbach

[email protected]

Dasong Dai Brunel University [email protected]

Igor Dobovsek University of Ljubljana [email protected]

Michaela Eder Max Planck Institute for Colloids and

Interfaces

[email protected]

Mizi Fan Brunel University [email protected]

Kristofer Gamstedt Royal Institute of Technology (KTH) [email protected]

T. Christian Gasser Royal Institute of Technology (KTH) [email protected]

Notburga Gierlinger Johannes Kepler University [email protected]

Peter Hansen Innventia AB [email protected]

Jonathan Harrington SCION [email protected]

Karin Hofstetter Vienna University of Technology [email protected]

Joanna Hornatowska Innventia AB [email protected]

Andrew Horvath Mondi Frantschach GmbH [email protected]

Katarina Jonasson Tetra Pak [email protected]



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Name Company E-mail

Andreas Jäger Vienna University of Technology [email protected]

Pasi Kallio Tampere University of Technology [email protected]

Lisbeth Kappel Graz University of Technology [email protected]

Viivi Koivu University of Jyväskylä [email protected]

Ron Lai Eka Chemicals [email protected]

Albertas Laurinavicius Semiconductor Physics Institute [email protected]

Tom Lindström Innventia AB [email protected]

Carl-Henrik Ljungqvist Stora Enso [email protected]

Bo Madsen Technical University of Denmark [email protected]

Mikael Magnusson Royal Institute of Technology (KTH) [email protected]

Arttu Miettinen University of Jyväskylä [email protected]

Ragnar Molander Stora Enso [email protected]

Petri Mäkelä Innventia AB [email protected]

Parviz Navi Bern University [email protected]

Cristian Neagu EPFL [email protected]

Mikael Nygårds Innventia and KTH [email protected]

Arnould Olivier University of Montpellier 2 [email protected]

Anne-Mari Olsson Innventia AB [email protected]

Alexander Pfriem TU Dresden [email protected]

Vilija Pranckeviciene Kaunas University of Technology [email protected]

Jelena Bogdanovic

Pristov

University of Belgrade [email protected]

Ksenija Radotic Institute for Multidisciplinary

Research

[email protected]

Pooya Saketi Tampere University of Technology [email protected]

Lennart Salmén Innventia AB [email protected]

Robert Sandell Innventia AB [email protected]

Robert Schennach Graz University of Technology [email protected]

Stephen Shaler University of Maine [email protected]

Karin Sjöström Södra [email protected]

Anders Skoglund Iggesund Paperboard [email protected]



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Name Company E-mail

Hüseyin Sivrikaya Bartin University [email protected]

Bengt Svennerstedt Swedish University of Agricultural

Science

[email protected]

Emil Tang Engelund Danish Technological Institute [email protected]

Heiko Thoemen University of Hamburg [email protected]

Fredrik Thuvander Karlstad University [email protected]

Anders Thygesen Technical University of Denmark [email protected]

Lisbeth G. Thygesen University of Copenhagen [email protected]

Pekka Tukiainen Helsinki University of Technology [email protected]

Ibrahim Tümen Bartin University [email protected]

Kristina Ukvalbergiene Kaunas University of Technology [email protected]

Xiaoqing Wang Max Planck Institute of Colloids and

Interfaces

[email protected]

Christoph Wenderdel Institute für Holztechnologie

gemeinnützige GmbH Dresden (IHD)

[email protected]

Yafang Yin KTH

(Chinese Res. Inst. of Wood Ind.)

[email protected]

[email protected]

Mario Zauer TU Dresden [email protected]

Bo Zhang Max Planck Institute of Colloids and

Interfaces

[email protected]

Sören Östlund Royal Institute of Technology (KTH) [email protected]



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Workshop program

4 November, 2009 08.30 – 09.00 Opening Session

09.00 – 10.15 Invited Lectures Session I

Stephen Shaler (UMaine, USA)

Michaela Eder (MPI Golm, Germany)

10.15 – 10.30 Poster Session I

10.30 – 11.00 Coffee Break

11.00 – 12.15 Invited Lectures Session II

Robert Schennach (TU Graz, Austria)

Notburga Gierlinger (JKU Linz, Austria)

12.15 – 12.30 Poster Session II

12.30 – 13.50 Lunch (Restaurant Syster och Bror)

13.50 – 15.30 Invited Lectures Session III

Janis Andersons (University of Latvia, Latvia)

Joanna Hornatowska (Innventia, Sweden)

Parviz Navi (BFH Bern, Switzerland)

15.30 – 15.45 Poster Session III


16.15 – 17.30 Invited Lectures Session IV

Bo Madsen (RISO-DTU), Denmark

Lennart Salmén (Innventia, Sweden)

19.30 – Evening cocktail and Dinner at Hotel Nordic Light

5 November, 2009 08.30 – 08.55 Invited Lectures Session V

Kristofer Gamstedt (KTH, Sweden)

08.55 – 09.10 Poster Session IV

09.10 – 10.00 Invited Lectures Session IV

T. Christian Gasser (KTH, Sweden)

10.00 – 10.15 Poster Session V


10.45 – 12.45 Working Group Discussions

12.45 – 13.00 Break

13.00 – 13.30 General Discussion & Closing

13.30 – Lunch (Restaurant Q)



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Abstracts

Invited lectures



9

Multimodal testing of single fibers Stephen M. Shaler

University of Maine 5793 AEWC Building

Orono, ME 04469-5793 USA

[email protected]

Key words: micromechanics, wood, experimental characterization, material behavior

ABSTRACT Composite materials are increasingly used in building, automotive, and consumer applications. Their performance is influenced by a variety of factors including material organization and the properties of the constituents. Natural fibers used for composite materials (including paper) are discontinuous and in the case of wood fibers, have slenderness ratios which can be less than 100 with diameters on the order of 20 µm. The size and variability of these fibers has historically provided challenges to experimental determination of their micro-mechanical behavior.

The 1990‘s was a time of rapid development of computers (calculations) and computer based technologies (rapid data acquisition and control, digital imaging) which enabled new approaches to fiber testing. A technique to measure tensile properties of discontinuous fibers was developed with improved accuracy through the use of a ball and socket grip assembly, computerized miniature test frame, and low capacity in-line load cell [1]. The system allowed for rapid testing of up to 100 fibers per day. This represented a step change in performance over other approaches and facilitates addressing biological (juvenility, species, etc.) and process derived (acetylation, sizing) questions on fiber quality and micro-mechanical performance [2].

The basic tensile test frame has been combined with a variety of microscopic techniques including laser scanning confocal microscopy (LSCM), environmental scanning electron microscopy (ESEM), and confocal raman microscopy to enable multi-modal investigations of micron scale phenomena of single fibers. The use of digital image correlation (DIC) for detailed fiber surface strain measurements provides the ability to obtain more detailed information on the influence of defects [3]. This powerful tool has been commercially developed over the last 10 years and several vendors currently provide turnkey capabilities. Continued improvements in available instrumentation may allow for the surface (2-D) and volumetric (3-D) evaluation of representative volume elements (e.g. multiple fibers) of composite structures.

References [1] Groom, L.H., S.M. Shaler, and L. Mott. 1995. Characterizing micro- and macromechanical

properties of single wood fibers. Pages 13-18 in 1995 International Paper Physics Conference. September 11-14, 1995. Niagara-on-the-Lake, Ontario.

[2] Groom, L.H., L. Mott, and S.M. Shaler. 2002. Mechanical properties of individual southern pine fibers. Part I. Determination and variability of stress-strain curves with respect to tree height and juvenility. Wood Fiber Sci. 34(1):14-27.

[3] Mott, L., S.M. Shaler, and L.H. Groom. 1996. A technique to measure strain distributions in single wood pulp fibers. Wood Fiber Sci. 28(4):429-437



10

Exploring structure and deformation mechanisms of plant fibres Michaela Eder* and Ingo Burgert

Max-Planck-Institute of Colloids and Interfaces Department of Biomaterials

Am Mühlenberg 1 D-14476 Potsdam

[email protected] [email protected]

Key words: experimental micromechanics, single fibre tests, ESEM, light microscopy, X-rays

ABSTRACT First tensile tests on single plant fibres date back to the fifties of the last century. Since then, a large variety of different fibre isolation and testing techniques have been developed. With regard to their commercial relevance the main focus has been on the properties of pulp fibres of wood (e. g. Jayne 1959; Duncker and Nordman 1965, Page et al. 1972, Groom et al. 2002a). Over the years important information has been gained on how tensile properties and deformation behaviour are influenced by the selected tree species (Jayne, 1960), structural features, such as. microfibril angle (Page and El-Hosseiny, 1983) or the fibre location within the tree (Groom et al. 2002a; Groom et al 2002b; Mott et al. 2002). In order to study the natural structure-function relationships of plant fibres as well as the mechanical design of cell walls, Burgert et al. (2002) introduced a fibre preparation technique based on a mechanical isolation which retains the matrix macromolecules. By applying in-situ methods which combine fibre tensile testing with nano- and microstructural characterisation techniques (e. g. light microcopy, scanning electron microscopy, X-ray scattering and Raman spectroscopy) specific deformation patterns of the cell walls were elucidated (Gierlinger et al. 2006; Keckes et al. 2003; Thygesen et al. 2007; Eder et al. 2008). In this talk we intend to give an overview about distinctive structure-property relationships of plant fibres and current knowledge about deformation mechanisms in cell walls derived from in-situ fibre testing methods.

References [1] B.A. Jayne: Mechanical properties of wood fibres. Tappi, 42 (1959), 461-467.

[2] B. Duncker, L. Nordman: Determination of the strength of single fibres. Papper och Trä, 10 (1965), 539-552.

[3] D.H. Page, F. El-Hosseiny, K. Winkler, R. Bain: The mechanical properties of single wood-pulp fibres Part I: A new approach. Pulp Pap-Canada, 73 (1972), 72-77.

[4] L. Groom, L. Mott, S. Shaler: Machanical properties of individual Southern pine fibers. Part I. Determination and variability of stress-strain curves with respect to tree height and juvenility. Wood Fiber Sci, 34 (2002a), 14-27.

[5] B.A. Jayne: Wood fibers in tension. Forest Prod J, 10 (1960), 316-322.

[6] D.H. Page, F. El-Hosseiny: The mechanical properties of single wood pulp fibres. Part VI. Fibril angle and the shape of the stress-strain curve. J Pulp Paper Sci, 9 (1983), 1-2.

[7] L. Groom, S. Shaler, L. Mott: Mechanical properties of individual Southern pine fibers. Part III. Global relationships between fiber properties and fiber location within an individual tree. Wood Fiber Sci, 34 (2002b), 238-250.

[8] L. Mott, L. Groom, S. Shaler: Mechanical properties of individual Southern pine fibers. Part II. Comparison of earlywood and latewood fibers with respect to tree height and juvenility. Wood Fiber Sci, 34 (2002), 221-237.



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[9] I. Burgert, J. Keckes, K. Frühmann, P. Fratzl, S.E. Tschegg: A comparison of two techniques for wood fiber isolation – evaluation by tensile tests of single fibres with different microfibril angle. Plant Biology, 4 (2002), 9-12.

[10] N. Gierlinger, M. Schwanninger, A. Reinecke, I. Burgert: Molecular changes during tensile deformation of single wood fibers followed by Raman microscopy. Biomacromolecules, 7 (2006), 2077-2081.

[11] J. Keckes, I. Burgert, K. Frühmann, M. Müller, K. Kölln, M. Hamilton, M. Burghammer, S.V. Roth, S. Stanzl-Tschegg, P. Fratzl: Cell-wall recovery after irreversible deformation of wood. Nat Mater, 2 (2003), 810-814.

[12] L.G. Thygesen, M. Eder, I. Burgert: Dislocations in single hemp fibres – investigations into the relationship of structural distortions and tensile properties at the cell wall level. J Mater Sci, 42 (2007), 558-564.

[13] M. Eder, S. Stanzl-Tschegg, I. Burgert: The fracture behaviour of single wood fibres is governed by geometrical constraints: in situ ESEM studies on three fibre types. Wood Sci Technol, 42 (2008), 679-689.



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An interdisciplinary view on the strength of a fiber – fiber bond in paper Eduard Gilli†, Franz J. Schmied‡, Christian Teichert‡ Ulrich Hirn‡‡, Lisbeth Kappel‡‡, Wolfgang Bauer‡‡ and Robert Schennach†*

†Graz University of Technology, Institute of Solid State Physics CD-Laboratory for Surface Chemical and Physical Fundamentals of Paper Strength

Petersgasse 16/2, 8020 Graz [email protected]; [email protected]

‡University of Leoben, Institute of Physics CD-Laboratory for Surface Chemical and Physical Fundamentals of Paper Strength

Franz-Josef Straße 18, 8700 Leoben, Austria [email protected]; [email protected]

‡‡Graz University of Technology, Institute for Paper, Pulp and FiberTechnology CD-Laboratory for Surface Chemical and Physical Fundamentals of Paper Strength

Kopernikusgasse 24, 8010 Graz [email protected]

Key words: paper fiber, fiber – fiber bond, bond strength, binding model

ABSTRACT The strength of a piece of paper is determined to a large extent by the strength of the fiber – fiber bond. While paper strength is a very important parameter, especially for Kraft paper producers, surprisingly little is known about the fiber – fiber bond. In this paper an overview about the bonding mechanisms that have been suggested will be given. As can be seen in figure 1, five different bonding mechanisms have been postulated [1] before. The first one (top left in figure 1) is mechanical interlocking, which can be seen as a mixture of friction and an effect comparable to a Velcro fastening. The second mechanism (top right in figure 1) is the interdiffusion of cellulose molecules between the two bonded fibers. The third mechanism (middle left in figure 1) is hydrogen bonding between the cellulose molecules of the two fibers. The fourth mechanism (middle right in figure 1) is basically Van der Waals bonding between the fibers and the fifth bonding mechanism (bottom in figure 1) is the coulomb interaction between charged species in the two fibers. These bonding mechanisms will be discussed with respect to their possible influence seen from a surface science perspective.

Figure 1: Five different bonding mechanisms for two paper fibers (after [1]). To gain more insight into the bond strength of a single fiber – fiber bond between two paper fibers results of the determination of the bonded area from two independent analysis methods (polarization microscopy [2, 3] and microtomy [4]) will be discussed. This is the first prerequisite to be able to measure specific



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bond strength. The second prerequisite is a method to actually measure the bond strength between two paper fibers. Here an atomic force microscopy based approach will be discussed.

A model system that can be used to investigate the influence of hemicelluloses on the bond between two cellulose surfaces will be presented briefly. Here the surface chemistry and the tribology of the surface will be investigated.

Finally it will be shown how the results of these approaches could be used to get a more detailed understanding of how large the influence of the five different bonding models on the overall binding strength is. Such an improved model of the bond between individual paper fibers can then be used to enhance our understanding of paper strength.

References [1] T. Lindström, L. Wagberg and T. Larsson, 13th Fundamental Research Symposium,

Cambridge, (2005) 457.

[2] D. H. Page, Paper Technology, 1 (4) (1960) 407.

[3] E. Gilli, L. Kappel, U. Hirn and R. Schennach, Composite Interfaces, in press.

[4] L. Kappel, U. Hirn, W. Bauer and R. Schennach, Nordic Pulp and Paper Research Journal, 24 (2) (2009) 199.



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Wetting and tensile deformation of single spruce wood fibres followed by Raman microscopy Notburga Gierlinger1*, Michaela Eder2 and Ingo Burgert2

1Institute of Polymer Science, JKU Linz [email protected]

2 Max-Planck Institute of Colloids and Interfaces, Department of Biomaterials

14424 Potsdam

Key words: single wood fibre, Raman microscopy, cellulose, microfibril orientation,

ABSTRACT To meet the natural demands of a tree, wood tissues are formed in various ways with different anatomical, chemical and physical characteristics and as a result wood properties differ widely. To gain insights at a molecular level during tensing and wetting, Raman spectra are acquired in situ. Molecular changes are monitored by following changes in Raman bands attributed to characteristic functional groups of the wood polymers. In a normal dry spruce wood fibre the band at 1095 cm-1, corresponding to the stretching of cellulose (C-O-C), is shifted during tensing linear towards shorter wavenumbers (-8 cm-1), demonstrating that the cellulose molecule is subjected to a uniform stress deformation [1-2].

Juvenile wood is less stiff and has a higher microfibril angle and the stress strain curves show clear differences in the dry and wet state. Wetting the fibre under tension (30mN), the load on the fibre and cellulose molecule is relieved, as seen in a drop in the force as well as in the shift of the 1095cm-1 band back to initial values (Fig. 1A). The continued force-elongation curve in the wet state is less steep and the 1095cm-1 band correspondingly. A second stop at 60 mN leads to a relaxation (drop in force), but the load on the cellulose (1095cm-1) is constant and at the end slightly increasing. Ongoing tensing leads again to stiffening and an increased stretching of the cellulose, followed by slipping and finally rupturing (Fig. 1A). A B

time [s]0 200 400 600 800

forc

e [m

N]

0

20

40

60

80

100

MFA

[°]

0

10

20

30

40

H20

STOP STOPTENS TENS TENS

time [s]0 200 400 600 800

forc

e [m

N]

0

20

40

60

80

100

wav

enum

ber [

cm-1

]

1086

1088

1090

1092

1094

1096

H20

STOP STOPTENS TENS TENS

Figure 1: Changes in force (black line) and A) the load on the cellulose molecule by plotting the position of the 1095cm-1 band (black dots) and. B) change in orientation of the cellulose microfibril (microfibril angle MFA, black dots) during tensing and wetting of a dry single spruce juvenile wood fibre.

From the band characteristics also conclusions on the cellulose microfibril orientation can be drawn [3]. Plotting the microfibril orientation changes during wetting suggests a straightening of the crystalline cellulose chains by swelling of amorphous components (Fig. 1B). During tensing in the wet stage further reorientation was seen (Fig. 1B).



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References [1] N. Gierlinger; M. Schwanninger, A. Reinecke, I. Burgert: Molecular changes during tensile

deformation of single wood fibers followed by Raman microscopy. Biomacromolecules, 7 (7) (2006), 2077-2081.

[2] N. Gierlinger; I. Burgert,: Secondary cell wall polymers studied by Confocal Raman microscopy: Spatial distribution, orientation and molecular deformation. New Zealand Journal of Forestry Science, 36 (1) (2006), 60-71.

[3] N. Gierlinger; S. Luss, Ch. König, J. Konnerth3, M. Eder, P. Fratzl: Cellulose microfibril orientation of Picea abies and its variability on the micron-level determined by Raman imaging. Journal of Experimental Botany, under review.



16

Tensile strength of single fibers: test methods and data analysis Janis Andersons

Institute of Polymer Mechanics, University of Latvia 23 Aizkraukles iela, Riga LV1006, Latvia

[email protected]

Key words: fibers, tensile strength, Weibull distribution, fragmentation test

ABSTRACT The load-bearing capacity of fiber-reinforced materials is to a large extent determined by the tensile strength of the fibers. The latter typically exhibits marked scatter thus warranting a statistical treatment. Weakest-link character of fiber failure is reflected in the commonly used Weibull two-parameter distribution of fiber strength:

( )⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

α

βσσ

0

exp1llP (1)

where σ is the tensile stress at fiber failure, α, β designate Weibull shape and scale parameters, l stands for fiber length, and l0 is a length unit. There is, however, growing experimental evidence that Eq. (1), while accurately describing strength scatter at a fixed fiber length, may not comply with the observed strength variation with fiber length. Instead, the modified Weibull distribution:

( )⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

αγ

βσσ

0

exp1llP (2)

with 10 ≤≤ γ is found to better agree with strength data of inorganic (glass, carbon) and natural organic (flax, jute, wool) fibers.

The origin of Eq. (2) and physical interpretation of its parameters is discussed. The most common strength test methods, fiber tension test (FTT) and fiber fragmentation test (FFT), are applied to evaluate Eq. (2) parameters. It is demonstrated, by an example of E-glass fibers, that FFT provides sufficient information to accurately estimate the parameters of the modified Weibull strength distribution for brittle linear elastic fibers. By contrast, pronounced scatter in the mechanical response of natural fibers, e.g. variability of modulus of elasticity, is shown to complicate the relation between the limit strain distribution provided by FFT and the fiber strength distribution obtained by FTT.

Assuming that the strength of agrofibers is governed by mesoscopic cell wall defects, fiber strength distribution in terms of defect density and severity is derived and found to approach Eq. (2) in the limit of a high defect density. Identifying the defects with kink bands in flax fibers, strength distribution Eq. (2) parameters are determined based on FTT at a fixed fiber length and kink band density measurements by optical microscopy. Thus obtained distribution function is further applied to successfully predict flax fiber strength at different lengths and the strength of flax fiber reinforced polymer matrix composites. The results obtained suggest that the modified Weibull distribution accurately describes the strength of both, inorganic and natural organic fibers. The strength testing can be made less tedious by combining FTT with (or replacing by) FFT.



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Fracture mechanisms observed during tensile testing of single fibres Joanna Hornatowska

INNVENTIA AB Box 5604, SE-114 86 Stockholm

[email protected]

Key words: single fibre, softwood fibres, environmental SEM, tensile testing, fibre fracture

ABSTRACT Tensile tests of single fibres were carried out to study changes of the fibre structure and fracture mechanism using environmental SEM. Industrially manufactured unbleached and bleached softwood fibres were investigated with regard to most often noted permanent deformations of fibre wall structure. The studies showed that fibre deformations should be treated as weakening of the fibre structure and fibre strength. All types of fibre deformations laying perpendicularly to fibre axis contributed to crack arising or to fibre breakage. However, fracture mechanisms were different for earlywood and latewood fibres. The fracture of the earlywood fibres was observed most often in the pit areas or very close to them whereas the fracture of latewood fibre occurred in areas with small local defects/damages as wrinkles in the fibre cell wall. The breakage occurred most often perpendicularly to the fibre axis. Areas with disorders of the fibre structure such as dislocations or microcompressions behaved more elastic and tensile testing caused principally arising of microcracks. This is illustrated in figure 1. Generally, the fracture was very seldom observed in those areas, where the fibre structure was very strongly disordered.

The fracture mechanisms were very similar for unbleached and bleached softwood fibres. Besides observations of crack development and fracture behaviour, measurements of fibre tensile strength were made outside ESEM in laboratory conditions (at 23 ºC and 50% RH) using single fibre tester constructed at Innventia. More comprehensive studies are planned to analyse relationship between forces to breakage and different kind of fibres and deformations.

a) b)

Figure 1. ESEM micrograph illustrating the same area of a latewood fibre with micro-compressions a) before loading and b) after loading during tensile testing. Note arising of microcracks.



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Micromechanics of single wood fiber; testing and modeling Parviz Navi† and Marjan Sedighi-Gilani†*

†Bern University of Applied Sciences, Architecture, Wood and Civil Engineering Sotothurnstrasse 102, P.O.

2500 Biel, Switerland [email protected]

†*Institute of Materials Science, Ecole Polythechnique Féférale de Lausanne, 1015 Lausanne, Switzerlan

[email protected]

Key words: micromechanics, wood fiber, experiment, modeling

ABSTRACT There are numerous experimental studies showing the behavior of single wood cells in tension. All these experiments indicate the tensile behavior of single wood cells is complex and cannot be described by a simple linear elasticity. On the other hand, estimation of the elastic properties of cell wall has been the subject of several researches using different approaches from 2-dimensional to 3-dimensional multi-scale modeling. In spite of these sophisticated approaches, These models can only predict the behavior of single tracheids in the elastic zone and no model exist to explain the complex stress-strain behavior of single wood tracheids after the yield point.

To gain insight into the complex behavior of single wood tracheid, wood tracheids were subjected to controlled cyclic tensile loading. The cyclic tensile load-extension curves show three distinct segments. The first segment is almost a straight line. At some level of loading, a yield point is observed and beyond this point the specimen undergoes large permanent deformations. In this segment, the specimen macroscopically behaves like an elasto-plastic material with positive hardening. However, the rigidity of the specimen after the yield point increase slowly as the load is further increased. The slope of the curve increases significantly (third segment) with no evidence of yielding occurring in this segment. Based on these experimental results, a micromechanical model was built to explain the elasto-plastic behavior of a single wood tracheid by occurrence of matrix degradation (yielding; mainly breaking of hydrogen bonds), local decrease of MFA and bonding hydrogen bonds of the hemicelluloses. In this model, two important hypotheses were made; first considered that the MFA are non-uniform along a tracheid and second considered the possibility of local degradation of the matrix (breaking and re-forming the hydrogen bonds). However, each of these hypotheses should be verified by experimentations.

The main objective of this work was to explain the underlying mechanisms underlying in the complex behavior of single wood tracheid under tension. It is concluded that successive damaging-reforming of the matrix and local reduction of MFA are possibly responsible for the complex behavior of wood tracheids.



19

Mechanical testing of spider silk Bo Madsen

Materials Research Division, Risoe National Laboratory for Sustainable Energy, Technical University of Denmark

Frederiksborgvej 399, DK-4000 Roskilde, Denmark [email protected]

Key words: spider silk, mechanical properties, tensile testing

ABSTRACT Spider silk has become a benchmark for modern polymer fibres and extensive research is being devoted to understanding and, eventually, copying these silk fibres [1]. It is an exceptional material; produced by the animal under ambient temperatures and pressures, and with water as solvent, and yet with mechanical properties comparable to those of the toughest man-made high-performance fibres.

Mechanical testing of spider silk is a means of linking information on molecular structure and composition with the properties of the silk. Measurement of the mechanical properties of silk is however not a trivial task. Spider silk fibres are only a few micrometers thick, and to avoid damaging or even breaking the fibres, micro-manipulators are needed for the handling. Moreover, sensitive equipment is needed to accurately measure their dimensions, as well as their load-displacement characteristic. Finally, spider silk is produced by living organisms, i.e. the spiders, which are controlling its properties, and this makes the species of spiders, the living conditions of the individual spiders and the sampling of silk important aspects in the mechanical testing of spider silk [2-4].

The presentation will give an introduction to spider silk and its properties. The applied method of mechanical testing of spider silk will be presented, as well as some of the obtained results; Figure 1 shows results of testing of silk from different spider species giving strength in range 0.8-1.5 GPa and toughness in the range 120-200 MJ/m3. Finally, some findings of the current spider silk research will be shown.

Figure 1: Stress-strain characteristics of silks sampled from 5 different species of spiders [3].

References [1] D. Porter, F. Vollrath: Silk as a biomimetic ideal for structural polymers. Advanced Materials, 21

(2009), 487-492. [2] B. Madsen, F. Vollrath: Mechanics and morphology of silk drawn from anaesthetized

spiders. Naturwissenschaften, 87 (2000), 148-153.



20

Single fibre testing – relation to variability Lennart Salmén

INNVENTIA AB Box 5604

SE-114 86 Stockholm, Sweden [email protected]

Key words: fibre testing, wood fibres, creep, moisture, temperature, modelling

ABSTRACT Fibre testing of wood fibres is a difficult task, which not only is related to the small dimensions of wood fibres in general but related to their large variability and susceptibility to acquire damages during the isolation process. Thus in order to obtain reliable fibre testing data different strategies may apply; i.e. to test a considerable number of fibres obtaining average values, to fully characterise the full morphology of each fibre tested including its damaged areas, relating properties to these, to measure the influence of variables and relate properties to these. In this presentation the last strategy has been adopted. With the use of only relative measurements of fibre properties the set-up is in a way also more forgiving towards deficiencies in the testing arrangement. To some extent this relates to the difficulties in deformation measurements on this small scale; the relative effect being less affected.

In this presentation a set–up for tensile testing of single fibres in the range of 1 to 2 mm in length is presented. Fibres are mounted in the tensile testing device using a mechanical support in the arrangement of the clamps. The glue used has been found to be sufficiently strong, not to flow into the fibre to any appreciable extent and to be inert towards moisture. This ensures reliable fibre tests in the range of interest. The tests performed have preferably been creep tests [1], where different variables have been investigated. In particular it was noticed that the fibril angle had the outmost importance for the relative magnitude of the mechano-sorptive creep, being smaller the lager the fibril angle. Effects of moisture scanning on fibre properties are also presented and discussed in relation to fibre modelling [2]. This demonstrates the assets of coupling modelling to targeted fibre measurements for increased understanding of structural effects of the wood fibre wall.

References [1] A.-M. Olsson, L. Salmén, M. Eder, I. Burgert: Mechano-sorptive creep in wood fibres Wood Science

Technol. 41(2007) 1: 59-67.

[2] L. Salmén: The cell wall as a composite structure in Paper Structure and Properties, ed. J.A. Bristow, P. Kolseth, Marcel Dekker Inc., New York, 1986, p. 51-73.



21

Constitutive modeling of soft biological tissues with emphasis on the vasculature T. Christian Gasser

Department of Solid Mechanics Royal Institute of Technology (KTH)

Osquars Backe 1 SE-100 44 Stockholm, Sweden

[email protected]

Key words: Structure, Anisotropy, Collagen, fibrous tissue, Finite Strain, Finite Element Method

ABSTRACT Biomechanical simulations can effectively assist and improve clinical interventions, provide diagnostic information and be of potential aid in tissue engineering. The reliability of such simulations largely depends on the underlying constitutive descriptions, and hence, constitutive modeling of soft biological tissues became an active field of research within the last few decades [1]. Continuum based constitutive relations describe the gross behavior that results from the internal constitution and allow the investigation of structural and functional interrelation in response to mechanical loading. This knowledge is crucial for the predictive capability of constitutive models and to gain insights into the physiological and the pathological load carrying mechanisms of soft biological tissues, i.e. to understand the interplay of mechanical load and cell signaling [1].

The vascular wall is a composite of cellular and extracellular constituents, where collagen type I is the most abundant protein that confers mechanical stability, strength and toughness. In details, triple helical protein chains, i.e. tropocollagen (1.5 nm in diameter; 300 nm in length) are parallel staggered into fibrils (thickness ranging from 50 nm to a few hundred nm), which in turn form more complex hierarchical structures like bundles of collagen fibrils.

The arrangement of collagen is thought to determine the macroscopic mechanical properties of vascular tissue, and this paper discusses different approaches to incorporate the collagen structure into macroscopic constitutive models. In particular, anisotropic hyper-elastic formulations for fibrous tissues are developed within the frame of finite strain continuum mechanics [2]. Constitutive models have been implemented in Finite Element software and polarized light microscopy and in-vitro mechanical testing has been used to identify structural and material parameters from of tissue samples, respectively. Finally, structural simulations aim at demonstrating the feasibility of the proposed approaches and emphasize advantages of biomechanical field variables as diagnostic determinants, e.g., to assess the rupture risk of Abdominal Aortic Aneurysm.

References [1] J.D. Humphrey, Cardiovascular Solid Mechanics. Cells, Tissues, and Organs, Springer-Verlag, New

York, 2002.

[2] T.C. Gasser, R.W. Ogden and G.A. Holzapfel. Review - Hyperelastic modelling of arterial layers with distributed collagen fibre orientations, J. Royal Soc. Lond. Interface, 3 (2006), 15 – 35.



22

Finite Element Modelling of Tensile Tests of Geometrically Well-Characterized Single Wood Fibres E. Kristofer Gamstedt

Department of Fibre and Polymer Technology Royal Institute of Technology (KTH),


Key words: micromechanics, finite element modelling, single fibre, stiffness, stress analysis

ABSTRACT Mechanical testing on single-fibre level is essential and very useful to relate the microstructure to macroscopic engineering (mechanical) properties of wood materials or wood-fibre based composites. Since wood cells are hardly prismatic, i.e. their cross-section varies along the length, and they are provided with pits, the deformation on tensile loading is non-uniform. This structural inhomogeneity results in local variations in buckling and twist along the fibre loaded in tension from end clamps. The aim of the present work was to investigate how the cell-wall stiffness transfers to that of the fibre, in the presence of natural cross-sectional variation along the fibre, characterized by microtomy.

The results presented here come mainly from the MS thesis of Dennis Wilhelmsson (KTH Solid Mechanics), supervised jointly by the author, Cristian Neagu (now EPFL) and Stig Bardage (SLU). From microtomed axial section of wood fibres, CAD software was used and the 3D geometry was exported to Abaqus FEM software, where the cell-wall layers S1, S2 and S3 were accounted for, with varying microfibril angles. Shell elements were compared with solid elements, and virtual tensile tests were performed, with and without twist constraints. The stiffness of an exact analytical model for concentric prismatic cylinders was invariably about 10 % higher than that from the finite element simulations of geometrically characterized softwood fibres. This can be explained by the additional buckling and twist deformation mode present in fibres due to the variation in cross-section along the fibre axis. It can be concluded that stiffness measures from tensile tests of single fibres can not directly be transferred to that of the cell-wall material. Furthermore, stress analysis with a experimentally calibrated failure criterion could indicate locations of failure (see figure), which were in concert with fractographic investigations.

Figure 1: Three dimensional stress analysis and comparison with a Tsai-Hill failure in tensile loading of a geometrically well-characterized wood fibre. Hot-spots indicate zones of probable failure.



23

Abstracts

Poster sessions



25

Tensile strength of bundles of softwood fibres Lupita Sierra Beltran†*and Erik Schlangen†

†Microlab, M & E, Faculty of Civil Engineering and Geosciences, Delft University of Technology

P.O. Box 5048 2600 GA Delft, The Netherlands

*[email protected] [email protected]

Key words: softwood, tensile strength, experimental characterization, material behaviour

ABSTRACT In order to use bundles of softwood fibres as reinforcement for cementitious materials the tensile strength of these bundles have been determinated using direct tension tests. To prepare the bundles 2 processes have been followed. First, small lumber blocks of spruce and larch (1x1x2 cm3) were cooked following a neutral sulphite semichemical (NSSC) pulping procedure [1]. After washing the blocks with fresh water, bundles of about 65 fibres have been manually taken apart. Secondly, pine wood bundles of about 160 fibres were cut from veneer sheets using a microtrome (Fig 1). Because of the production process, the pine bundles have rectangular shape and a bigger and more uniform cross section than the spruce and larch bundles. The bundles have been tested under direct tensile strength using a micro tension-compression testing device (developed by Kammrath & Weiss) (Fig. 2). The bundle was glued to two steel non-rotating loading plates prior to being test under deformation control. The tests results are shown in Table 1. The tests have been done inside the ESEM (Fig. 3) allowing to observe the fracture process of the bundles as well as their lateral deformation. This lateral deformation appears to be less than 1%, thus the Poisson ratio is null for these bundles.

Fig.1: ESEM image of pine bundle Fig.2: Bundle tensile test setup Fig.3: ESEM image after test

Table 1: Dimensional and mechanical properties of the bundles

Fibre Tensile strength σf (MPa) Young’s modulus Ef (GPa) Area (mm2) Spruce 663 39 0.055 Larch 708 34 0.041 Pine 730 29 0.113

References [1] J.C.F. Walker: Pulp and paper manufacture, in Primary wood processing principles and practice.

Springer, 2006.



26

Characteristic and performance of elementary hemp fibres Dasong Dai† and Mizi Fan†*

†Researcher, †*Director Nano Cellulose and Composites Research Centre (NRC3)

Brunel University, West London, UB8 3PH, UK [email protected]

[email protected]

Key words: elementary hemp, microstructure defect, experimental characterization, micro failure mechanism

ABSTRACT A comprehensive experimental study has been carried out to ascertain the properties of elementary hemp fibres. Characteristics, failure modes and strength of elementary hemp fibres have carefully been determined by using microscopic techniques and their correlations established.

There have been many investigations of the strength of hemp fibres, however, it is not possible to use or appropriate to compare data reliably from different investigations reported in the literatures. Measuring natural fibres proves to be a great challenge. Micro-structural defects, fibre abstraction (e.g. single fibre) and processing technology are yet to be studied. This paper is an attempt to characterize the surface and reveal the failure mechanisms of elementary hemp fibres that have occurred by using microscopic techniques. By observing carefully the fracture modes the factors affecting their respective failure could be determined, and the realistic and accurate properties of elementary hemp fibres obtained. The results showed that there exist various deformation/defects in the single elementary hemp fiber (e.g. kink bands, dislocations, nodes, slip planes) which may be the weak points to initiate the failure under an applied stress. The micro-architecture of hemp cell wall is another critical parameter contributing to the failure of the fibres. The primary wall and secondary wall showed different deformation and breaking behavior: crack (breaking) initiates in a weak point of primary wall and subsequently propagates along radial direction. The order of breaking was: primary wall, S1 layer, S2 layer. The average S2 layer microfibril angle of the broken surface was about 6.16°, which was much bigger than the average microfibril angle of normal hemp S2 layer (2.8° for the fibres tested), indicating that the breaking of hemp fibre occurs at the points where have the biggest microfibril angle.



27

Measuring the bonded area of individual fiber-fiber bonds Lisbeth Kappel†*, Ulrich Hirn†, Wolfgang Bauer† and Robert Schennach‡

†Institute for Paper, Pulp and Fiber Technology Kopernikusgasse 24/II, 8010 Graz

[email protected]

‡Institute for Solid State Physics Petersgasse 16/II, 8010 Graz [email protected]

Key words: Fiber-fiber bonds, bonded area, fiber morphology, microtome serial sectioning

ABSTRACT This paper presents a method for the determination of bonded area of single fiber-fiber bonds, based on microtome serial sectioning and image analysis. The size and three dimensional structure of the bonded area are assessed together with cross sectional fiber morphology.

The method is based on an automated microtomy system [1], the major steps are shown in Figure 1. Slices with a thickness of 3 µm are repeatedly cut off the embedded sample with the microtome and the cutting area is imaged automatically after every cut. This yields a stack of images of the fiber-fiber bond cross section, representing the three-dimensional shape of the bond. For every cut the line where the fibers are in optical contact is determined with image analysis and its length is measured. Bonded area is calculated from bond line length multiplied with the cut thickness. In addition to bonded area several morphological parameters of fibers and bonding region are measured image analytically using a procedure described by [2].

Figure 1: The same fiber-fiber bond under the microscope (a), in serial sectioning (b-d), after image analysis of one slice (e) and visualization of the 3D bonding area (f).

References [1] M. Wiltsche, M. Donoser, W. Bauer and H. Bischof (2005): A New Slice-Based Concept for 3D

Paper Structure Analysis Applied to Spatial Coating Layer Formation. 13th Fundamental Research Symposium, Cambridge, 853.

[2] J. Kritzinger, M. Donoser, M. Wiltsche and W. Bauer (2008): Examination of Fiber Transverse Properties Based on a Serial Sectioning Technique. Progress in Paper Physics Seminar Proceedings, Helsinki, 157.



28

Three dimensional single fibre imaging in micro- and nano-scales Viivi Koivu, Tuomas Turpeinen, Markko Myllys, Jussi Timonen and Markku Kataja

University of Jyväskylä Department of Physics

P.O. Box 35 FI-40014 Jyväskylä

E-mail: [email protected]

Key words: X-ray nano tomography, X-ray micro tomography, fiber, structural characterization

ABSTRACT X-ray tomography is a method to produce 3D digital representations of real physical samples by mathematically reconstructing projection data collected by illuminating the sample with X-rays from many directions [1]. The method has been applied to various macro and micro-scale analyses of fibrous materials. Now imaging is possible also in nanoscopic length scales allowing rigorous analysis of fiber structures and even single fibers. In this work main details and procedures related to imaging of single fibers with XRadia [2] MicroCXT and nanoCXT devices are demonstrated, see Fig. 1.

Figure 1: Single wood fibre imaged in (a) micro-scale (voxel size 0.3 µm) and (b) nano-scale resolution (voxel size 30 nm)

References [1] A. C. Kak and Malcolm Slaney, Principles of Computerized Tomographic Imaging, Society of

Industrial and Applied Mathematics, 2001.

[2] http://www.xradia.com/

[3] B. Madsen, S. Zheng Zhong, F. Vollrath: Variability in the mechanical properties of spider silks on three levels: interspecific, intraspecific and intraindividual. International Journal of Biological Macromolecules, 24 (1999), 301-306.

[4] F. Vollrath, B. Madsen, S. Zheng Zhong: The effect of spinning conditions on the mechanics of a spider’s dragline silk. Proceedings of the Royal Society B, 268 (2001), 2339-2346.

(a) (b)



29

An automated method to recognize individual fibers from three-dimensional tomographic images Arttu Miettinen*, Viivi Koivu, Tuomas Turpeinen, Jussi Timonen, and Markku Kataja

Department of Physics University of Jyväskylä

P.O. Box 35 (YFL) FI-40014 Jyväskylä Finland

[email protected]

Key words: tomography, wood fiber composite, segmentation, fiber tracking

ABSTRACT A method to separate individual fibers from a three-dimensional binarized tomographic image of a fibrous material is presented. The method consists of several steps which classify and merge areas of three-dimensional surface skeleton of the fiber network. Classify/merge –decisions are made based on topological properties of the skeleton. The presented algorithm is fully automatic and requires no manual preselection of candidates to be identified as fibers. It generalizes a similar method introduced in Ref. [1] to tubular and irregularly shaped fibers.

The algorithm facilitates various measurements related to individual fibers and fiber contacts. Especially, it makes it possible to characterize changes in properties of individual fibers due to processing and manufacturing of the material. Figure 1 shows the fibers recognized in an X-ray tomographic image of a wood fiber reinforced composite material.

Figure 1: Segmented individual fibers in wood fiber composite material. Each recognized fiber is colored with random color.

References [1] H. Yang, B. W. Lindquist: Three-dimensional Image Analysis of Fibrous Materials, Proc. SPIE,

4115 (2000), 275-282.



30

Modelling the hygroexpansion of normal and compression wood tracheids R. Cristian Neagu†, E. Kristofer Gamstedt†* and Stig L. Bardage‡

†Laboratoire de Technologie des Composites et Polymères (LTC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

[email protected] †*School of Chemical Science and Engineering, Fibre and Polymer Technology

Royal Institute of Technology (KTH), Teknikringen 58, SE-100 44 Stockholm, Sweden [email protected]

‡Department of Wood Science, Swedish University of Agricultural Sciences (SLU),

P.O. Box 7008, SE-750 07 Uppsala, Sweden [email protected]

Key words: micromechanics, wood, hygroexpansion

ABSTRACT The influence of the ultrastructure on the hygroexpansion of single normal wood (NW) and compression wood (CW) tracheids has been analysed with a micromechanical model [1] and a three-dimensional helically orthotropic model of concentric cylinders [2]. The fibre cell wall layers (S1,S2 and S3) are coaxially assembled into a multilayered cylindrically anisotropic tube which is subjected applied fictitious hygroscopic loads. The properties of the main wood polymers were taken from literature and accounted for change in properties of the hemicelluloses and lignin with moisture content [1]. The dimensions, microfibril angle (MFA) and layerwise structure of typical conifer CW and NW tracheids were as well taken from literature. Since the main material axes have a chiral orientation in the secondary layers, twist-extension coupling and hygroscopic torsion are predicted. The hygroexpansion properties of constrained (as in wood) and free fibres (as in pulp) were simulated. Results show that the longitudinal hygroexpansion (βz) increases and the transverse or circumferential hygroexpansion (βθ) decreases with increasing MFA if a fibre is allowed to expand freely. This is expected since the hygroexpansion strains and elastic properties are inversely related. It is interesting to notice that βz of constrained NW fibres decreases with increasing MFA. The βz of constrained CW fibres is reduced significantly but it is still increasing with increasing MFA. These results are in accordance with the measured deformation response upon swelling of tracheids of NW (shrinkage) and CW (elongation), under the constraint of no torsional deformation [3].

References [1] Marklund E, Varna J. Modeling the hygroexpansion of aligned wood fiber composites. Composites

Science and Technology, 69 (2009), 1108-1114. [2] R.C. Neagu, E.K. Gamstedt: Modelling of effects of ultrastructural morphology on the hygroelastic

properties of wood fibres. Journal of Materials Science, 42 (2007), 10254-10274. [3] I. Burget, M. Eder, N. Gierlinger, R. Fratzl: Tensile and compressive stresses in tracheids are

induced by swelling based on geometrical constrains of the wood cell. Planta, 226 (2007), 981-987.



31

Fibre morphology – important for mechanosorptive creep Anne-Mari Olsson and Lennart Salmén

INNVENTIA AB Box 5604


Key words: Mechanosorptive creep, single fibres, testing, morphology, micro fibrillar angle

ABSTRACT The phenomenon of increased creep during changing moisture has been observed for long, both for wood and paper products. This accelerated creep, termed mechano-sorptive creep, is a complex phenomenon that has been extensively studied from the time of its discovery in the late 1950ties. It has been clearly shown that this phenomenon exists in single fibres [1] as well as in fibre networks. However the effect of the fibre morphology has not been clearly. In ordet to study this effect spruce single fibres with different micro fibrillar angle were tested, and the mechano-sorptive effect was determined.

Fibres from early wood and late wood of juvenile and mature wood were tested in a Perkin Elmer DMA (dynamic mechanical analyzer) [2]. Each fibre was tested in both constant and cyclic humidity conditions and the creep strain rate in the both conditions was compared.

Figure 1 shows that the microfibrillar angle is important for the mechano-sorptive creep. Fibres from juvenile earlywood with a high fibrillar angle were less sensitive to moisture variations than mature latewood fibres with low fibrillar angle.

Microfibril angle0 5 10 15 20 25 30

MSC

-rat

io

1.0

1.5

2.0

2.5

3.0

Microfibril angle0 5 10 15 20 25 30

MSC

-rat

io

1.0

1.5

2.0

2.5

3.0

Figure 1: The mechanosorptive creep effect as a function of the microfibrillar ange

References [1] Olsson, A-M, Salmén L. Eder M. Burget I. Mechano-sorptive creep in wood fibres. Wood Science

and Technology, Vol. 41, 2007.

[2] Dong, F. Mechano-sorptive creep - structural origin on the single fibre level. MSC Thesis work. Royal Institute of Technology (KTH), 2009.



32

Production and characterization of wood fibres with defined properties for their use as reinforcing fibres in wood-polypropylene-composites

Alexander Pfriem, Mario Zauer and Melanie Horbens

Technische Universität Dresden Institute of Wood and Paper Technology

01062 Dresden - Germany [email protected]

Key words: fibre length, fibre width, reinforcement, shape factor, wood-polypropylene-composites

ABSTRACT For wood fibres to be used as reinforcing fibres, for example in fibre reinforced plastics, they have to have defined material properties. For this it is necessary to produce fine-fibrillated wood fibres. Due to variation of outcrop strategy and condition, as well as appropriate methods of the fibrous material after-treatment and fractionation, a dispensable fibrous material was developed which showed a narrow, invariable and reproducible spectrum of technological properties.

Thermo-mechanical pulp of the wood species spruce (Picea abies Karst.) and beech (Fagus silvatica L.) served as reinforcing fibres. By means of a development of methods for the formation of wood-fibre agglomerates, it was possible to convert the fibre fractions into a reproducible form for the extrusion process. The break-up of the agglomerate compounds was evident from micro-cuts by optical microscopy.

Furthermore, the used fibre fractions were visually characterised by means of light microscopy and scanning electron microscopy as well as with regard to their fibre characteristics fibre length, fibre width, their distributions, shape factor and fibre curl. By means of a FiberLab measuring system, the frequency distributions of fibre length and width and the fibre curl were determined. The detected number of fibres is in the order of approximately 1,000 to 15,000 fibres. The influence of fibre morphology, shape factor and fibre content on the properties of wood-polypropylene-composites that can be injection moulded has been shown. Based on an evaluation of the bonding properties of the composite, fractionated spruce fibres of the TMP process having a distinctive single-fibre character and great shape factor exhibit the greatest reinforcing potential (Figure 1 presents the frequency distributions of fibre lengths and widths of this fraction). The use of the adhesion promoter MAH-PP enabled significant enhancements of composite properties with increasing fibre content while good fibre-matrix cohesion was maintained.

Figure 1: Fibre length and width of the spruce TMP-fraction showing highest reinforcing potential.



33

Variability and relation of lignin, low molecular mass phenolics and cell wall bound peroxidases in the needels of Serbian spruce (Picea omorika (Pančić) Purkynĕ) during four seasons

Jelena Bogdanović Pristov*, Aleksandra Mitrović, Vuk Maksimović, Daniela Djikanović, Dragosav Mutavdžić, Jasna Simonović and Ksenija Radotić

Institute for Multidisciplinary Research Bulevar Despota Stefana 142

11060 Beograd, Serbia [email protected]

Key words: cell wall, lignin, phenols, peroxidase

ABSTRACT We studied seasonal variation in the activity and isoenzyme pattern of cell wall bound peroxidase, as well as contents of lignin and simple phenols ester and ether bonds to the cell wall, in the needles of Picea omorika (Pančić) Purkynĕ trees. The samples were collected from the natural habitat of the species, Mt. Tara. Seasonal changes were found to affect enzymatic activities and isoenzyme profiles. Several isoforms of both ionic and covalent peroxidase were detected. The highest ionic peroxidase activity was attained in summer, while the highest activity of covalent peroxidase was attained in spring. The highest lignin content was found in spring. A GC-MS analysis of cell wall alkaline extracts has shown the presence of ferulic acid, p-coumaric acid and coniferyl alcohol, as well as dehydroferulic acid dimers, ferulic acid-coniferyl alcohol dimers and coniferyl alcohol trimers. These results may be an evidence of more extensive cross-links among wall polymers in P. omorika species. HPLC determined contents of ferulic acid, p-coumaric acid and coniferyl alcohol, released from the alkali treated cell walls, were lowest in spring. The low values of these phenols in P. omorika needles in spring show that polymeric structures of cell wall are less interconnected, meaning higher relaxation and loosening of the cell wall. This may be related to increased vegetative growth in this season. It was found a positive correlation of individual phenols esterified to the cell walls with the activities of some ionic and covalent POD isoforms in annual cycle. These results support hypothesis that certain ionic and covalent POD isoforms might be involved in formation of the cross-links between cell wall polymers in Serbian spruce needles.



34

Cell wall structural differences between hardwood and softwood studied by FT-IR, Raman and fluoresence spectroscopy Ksenija Radotić1*, Daniela Djikanović1, Jasna Simonović1, Jelena Bogdanović Pristov1, Aleksandar Kalauzi1, Danica Bajuk-Bogdanović2 and Milorad Jeremić1, 2

1Institute for Multidisciplinary Research, Kneza Višeslava 1

11000 Beograd, Serbia; *[email protected]

2Faculty of Physical Chemistry University of Belgrade,

Studentski trg 12 11000 Belgrade, Serbia

ABSTRACT The cell walls (CWs) of woody tissue are composed predominantly of cellulose, lignin, and hemicelluloses. There are chemical differences between the type of hemicelluloses, as well as between lignin monomeric precursors in the CWs of softwoods and hardwoods. Raman and FT-IR spectroscopy are complementary optical methods for monitoring composition differences in the CWs, as both lignin and polysaccharides have fingerprint regions in these spectra. Fluorescence spectroscopy is an intrinsic property of the cell walls. Deconvolution and modeling of the emission spectra is a sensitive analytical tool in studies of complex molecular structures. Since fluorescence of the cell walls originates from lignin and/or hydroxy-cinnamic bridges between wall polymers, this method gives data about lignin fluorophores in the cell wall.

We compared FT-IR, Raman and fluorescence emission spectra of the CWs isolated from the Picea omorika (Panč) Purkyne (softwood) and Acer platanoides (hardwood). The isolation of the CWs was performed according to the procedure of Chen et al. (Phytochem. Anal. 11, 2000, p 153). Raman and FT-IR spectra were measured using Thermo Scientific Nicolet Almega Visible Raman spectrometer and Termo-Nicolette 6700 FT-IR spectrometer (ATR), respectively. Fluorescence spectra were collected using a Fluorolog-3 spectrofluorimeter (Jobin Yvon Horiba, Paris, France) equipped with a 450W xenon lamp and a photomultiplier tube. In all measurements the cell wall samples were positioned in a front-face configuration in the measuring chamber. For each of the samples, a series of emission spectra were collected by varying excitation wavelengths with 5 nm steps, in order to trace all fluorophores in the cell walls. The deconvolution of all spectra of a sample, using a log-normal model, was performed in order to determine the number of fluorophores in the sample.

The bands in the FT-IR spectra of the Acer cell walls are more pronounced in comparison with those of the P. omorika cell walls, but there are no substantial differences in the spectral pattern. However, differences are much more pronounced in the Raman spectra of the two CW samples, in the lignin (band region of C = C vibrations being active in Raman) and polysaccharides characteristic regions. The spectral differences reflect different inter- and intramolecular connections in these CWs, caused by the chemical differences in precursors of hardwood and softwood CWs. Thus the results show different C = C bond organisation in the two CW samples. The emission spectra of the two CWs have similar shape, but differ in the spectral width. Deconvolution of the emission spectra has confirmed the difference in the long-wavelength region of the spectra, due to the difference in the corresponding fluorophores (mainly related to the lignin polymer) in the CWs of the two samples. This difference reflects chemical/structural distinction between lignin precursors in the hardwood and softwood (guaiacyl type in P. omorika and syringyl/guaiacyl type in Acer sp).

Understanding of the distinct interpolymer connections in the CWs of the hardwood and softwood species, may contribute to the studies and modeling of the isolated single polymers



35

Flexibility measurement of individual paper fibers using microrobotics

P. Saketi†, M. v. Essen† and P. Kallio†

†Micro- and Nano Systems Research Group, Tampere University of Technology

Tampere, Finland [email protected]

[email protected] [email protected]

Key words: flexibility, microrobotics, MEMS, paper fibers

ABSTRACT Mechanical characterization of individual paper fibers (IPF) determines the key parameters which affect the quality of paper sheets. One of these key parameters is the flexibility of IPFs. Current laboratory tests are based on bulk paper fiber measurements. This poster presents a novel test bench to measure the flexibility of IPFs using a microrobotic platform and MicroElectroMechanical force sensors directly.

The test bench to measure the IPF flexibility is able to grasp the IPFs from their both ends as a both end fixed beam using two microgrippers, and determines the required force, F, to bend the IPF using a micromechanical force sensor (see figure). An integrated machine vision system provides the information about length of IPF, L, and the location at which the force is applied. In this test bench, the force is always applied in the middle of the IPF. The deflection, y, of IPF is measured using the position sensor which the force sensor is attached to.

Figure 1: Flexibility Measurement of an IPF.

The bending stiffness, EI, and the flexibility of IPFs are measured based on the beam theory [1] using Equation (1), where E and I are Young modulus and moment of inertia, respectively.

Flexibility = 1/EI = -192y/FL3 (1)Two sets of tests have been done using the test bench. The first set of tests has been done with bleached Pine pulp and the second set of the tests with the same pulp but S2 and S3 layers partly removed. The second sample shows relatively smaller bending stiffness and higher flexibility comparing to the first one. The results will be presented in the poster.

References [1] W. C. Young and R. G. Budynas, ”Roak’s Formulas for Stress and Strain-Seventh Edition”, ISBN

0-07-121059-8, McGRAW-Hill, 2002.



36

Fibre strength, stiffness and thickness of Swedish grown hemp – a study of plant development and fibre conditions B. Svennerstedt†*, T. Nilsson‡ and P.J. Gustafsson‡

† Associate Professor, Biofibre Technology Research Group, Department of Agriculture – Farming System, Technology and Product Quality,

Swedish University of Agricultural Sciences, P.O Box 86

SE-230 53 Alnarp, Sweden e-mail: [email protected]

‡ Techn. lic. and Professor, respectively Division of Structural Mechanics,

Lund University Box 118

SE-221 00 Lund, Sweden

Keywords: hemp, varieties, fibre, strength, stiffness, thickness

ABSTRACT Tensile strength and thickness of fibre bundles were tested for industrial hemp grown in southern Sweden during 2004-2006. Strength and stiffness of individual technical fibres were furthermore determined by testing the tensile stress versus strain performance.

The field trials included two monoecious varieties, Beniko and Futura 75, at seed rate of 30 kg/ha. The trials were harvested at one, two or three stages in the autumn each year. The tests of individual fibres comprised retted fibres of three different lengths, with and without embedment in glue. The glue embedment represented fibre performance within a composite material.

The mean strengths of the fibre bundles from hemp harvested at different times 2004-2006 were 304-353 MPa for Beniko and 257-496 MPa for Futura 75. The mean fibre thicknesses were found to be 111-133 μm for Beniko and 109-134 μm for Futura 75 [1].

The tests of individual technical fibres showed that fibre strength is significantly affected by both fibre length and glue embedment. The strength was, e.g., 820 MPa for glued fibres with length 3 mm and 420 MPa for unglued fibres with 27 mm length. The mean modulus of elasticity was 50.4 and 65.1 GPa for the unglued and glued fibres, respectively [2].

References [1] Svennerstedt, B. 2008. Hemp Biomass, Fibre Strength and Thickness – Trials in Southern Sweden

2004-2006. Proceedings of the 2008 International Conference on Flax and Other Bast Plants. July 21-23 2008. Saskatoon. Canada.

[2] Nilsson, T. 2006. Micromechanical Modelling of Natural Fibres for Composite Materials. Licentiate Dissertation, Report TVSM-3067, Division of Structural Mechanics, Lund University, Sweden.



37

Measuring fiber strength, using a single fiber fragmentation F Thuvander† and C H Ljungkvist‡

†Materials engineering Karlstad University

[email protected]

‡Publication paper R&D Stora Enso Research Karlstad

[email protected]

Key words: micromechanics, experimental characterization, material behavior, fiber fragemtation

ABSTRACT Wood is a heterogeneous material, where the cells, the tracheids that’s to the main part forms the material has further functions other than providing strength to the structure, mainly transport of water. The tracheids are further at the level of the cell wall adopted for the loading condition and is modified and adopted for the different usages. As a result we can identify different tracheids, in a softwood early wood and latewood compression wood all modified to adopt for their function.

When the wood tracheids are separated in a pulping process the fibers that then is the result varies in properties depending on the function they where adopted for. If then ever the effect on wood pulp fibers of different treatments is to be understood is a necessary to measure the properties of individual fibers.

Further structural variations in the cell wall like pores etc and damages that are introduced by processing may have influence.

Unfortunately measuring single fiber properties is a tedious process involving preparation and handling of the fibers.

Using single fragmentation techniques provides a tool to that enables separation and to sort the data for the different fibers. Further the technique enables assortment of data from observations on the fiber cell wall and results for damaged cell wall material can be compared to undamaged cell wall and cell wall materials with pores.

To enable this experimental procedure and equipment and is developed as well as a supportive computer code for analysis.



38

Analysis of strength of flax fibre bundles Anders Thygesen*, Bo Madsen, Anne Belinda Thomsen and Hans Lilholt

Risø DTU, Technical University of Denmark, Frederiksborgvej 399, 4000 Roskilde

[email protected]

ABSTRACT Bundle strength in flax fibres was measured by tensile tests along the fibre axis and recorded as the maximum stress value before fracture. Bundle strength is important since these are on a larger structural scale than single fibres. The fibre bundles have a size of 0.01 - 0.3 mm2 compared with 0.0001 - 0.001 mm2 for single fibres. Fibre bundle strength is of importance for strength of composite materials. Flax fibres were tested after field retting (a), field retting + scutching + carding (b) and field retting + scutching + carding + cottonization (c) at different cross sectional areas (S). A power law function was developed to fit the relationship between bundle strength and cross sectional area based on the Weibull distribution [1]:

0

0b b

SS

α

σ σ⎛ ⎞

= ⋅⎜ ⎟⎝ ⎠

The bundle strength decreased versus the cross sectional area of the fibre bundles after field retting and after the subsequent fibre processings. The data were fitted with the power law function, Figure 1, with α (a) = - 0.09 ± 0.04, α (b) = - 0.11 ± 0.04 and, α (c) = - 0.13 ± 0.05, and with σb0 (a) = 627 ± 81, σb0 (b) = 370 ± 47 and σb0 (c) = 202 ± 38. Comparative values at a cross sectional area of 0.1 mm2 showed fibre bundle strength of 775 ± 38 MPa after field retting only. Subsequent scutching and carding resulted in rough fibres with reduced strength of 474 ± 26 MPa. Additional cottonization resulted in fine fibres with strength of 273 ± 21 MPa. Overall this study shows that increased processing results in reduced bundle strength. The power law function is a convenient tool for the analysis of strength of flax fibre bundles due to an acceptable fit of the data.

Figure 1: Bundle strength versus cross sectional area for flax fibres after processing a, b and c. Each data point represents one strength measurement. The curves were established by power law regression of σb versus S.

Reference [1] W.Weibull: A statistical theory of strength of materials. Ing.Vetenskaps.Akad. Handl. nr.151(1939)

The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement nº 214467 (NATEX).



39

A developing in-situ inspection method on microstructure characteristics of wood deformation under loading Yafang Yin1, 2 *, Mingming Bian1, Bo Liu1 and Xiaomei Jiang1

1 Chinese Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China 2 Fiber and Polymer Technology Department, Royal Institute of Technology, Stockholm, Sweden

[email protected]; [email protected]

Keywords: in-situ inspection, microstructure characteristics, auto-focus, loading

ABSTRACT The objective of this abstract is to introduce an inspection method, which combines a micro-mechanical tester with a self-developing auto-focus photo collection system, to realize the in-situ detection on microstructure characteristics of wood deformation [1, 2] during different loading progress. Air-dried wood samples from Chinese fir (Cunninghamia lanceolata) plantation were selected. The micro-mechanical tester was used to load on small wood specimens. Meanwhile the auto-focus microscope equipped with long distance objective lens took photos to record the microstructure characteristics of wood deformation during loading progress. The loading data from mechanical tester and collecting photos could be input into the new developed software with a same time coordinate for further analysis and relationship construction between loading and microstructure characteristics. The present result shows that this method could provide both an in-situ inspection on microstructure characteristics of wood deformation in a specific time span and a quantitative analysis on microstructure variance under real-time loading conditions.

Figure 1: Cell deformation progress of Cunninghamia lanceolata earlywood under radial compression. 40X long distance objective lens. Long arrow indicates the location of cell deformation. Short arrow indicates ray cell. Bar = 100μm.

References [1] Tabarsa T, Chui Y H. Characteristic microscopic behavior of wood under transverse compression

part 1: method and preliminary test results. Wood and Fiber Science.2000, 32(2):144-152. [2] Gong, M., Li, L., Chui, Y.H., Li, K.C, and Yuan, N.X. Modeling of recovery of residual stresses in

densified softwoods. Proceedings of the 10th World Conference on Timber Engineering. Miyazaki, Japan. On Proceedings CD. 2008.

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