- COST Action FP0802

Transcription

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
1
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
[email protected]
Mönchengladbach
Dasong Dai
Brunel University
[email protected]
Igor Dobovsek
University of Ljubljana
[email protected]
Michaela Eder
Max Planck Institute for Colloids and
[email protected]
Interfaces
Mizi Fan
Brunel University
[email protected]
Kristofer Gamstedt
[email protected]
T. Christian Gasser
[email protected]
Notburga Gierlinger
Johannes Kepler University
[email protected]
Peter Hansen
Innventia AB
[email protected]
Jonathan Harrington
SCION
[email protected]
Karin Hofstetter
[email protected]
Joanna Hornatowska
Innventia AB
[email protected]
Andrew Horvath
Mondi Frantschach GmbH
[email protected]
Katarina Jonasson
Tetra Pak
[email protected]
2
Name
Company
E-mail
Andreas Jäger
[email protected]
Pasi Kallio
Tampere University of Technology
[email protected]
Lisbeth Kappel
[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
[email protected]
Arttu Miettinen
[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
[email protected]
Jelena Bogdanovic
University of Belgrade
[email protected]
Institute for Multidisciplinary
[email protected]
Pristov
Ksenija Radotic
Research
Pooya Saketi
[email protected]
Lennart Salmén
Innventia AB
[email protected]
Robert Sandell
Innventia AB
[email protected]
Robert Schennach
[email protected]
Stephen Shaler
University of Maine
[email protected]
Karin Sjöström
Södra
[email protected]
Anders Skoglund
Iggesund Paperboard
[email protected]
3
Name
Company
E-mail
Hüseyin Sivrikaya
Bartin University
[email protected]
Bengt Svennerstedt
Swedish University of Agricultural
[email protected]
Science
Emil Tang Engelund
Danish Technological Institute
[email protected]
Heiko Thoemen
University of Hamburg
[email protected]
Fredrik Thuvander
Karlstad University
[email protected]
Anders Thygesen
[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
[email protected]
Xiaoqing Wang
Max Planck Institute of Colloids and
[email protected]
Interfaces
Christoph Wenderdel
Institute für Holztechnologie
[email protected]
gemeinnützige GmbH Dresden (IHD)
Yafang Yin
KTH
[email protected]
(Chinese Res. Inst. of Wood Ind.)
[email protected]
Mario Zauer
TU Dresden
[email protected]
Bo Zhang
Max Planck Institute of Colloids and
[email protected]
Interfaces
Sören Östlund
[email protected]
5
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
15.45 – 16.15
Coffee Break
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
10.15 – 10.45
Coffee Break
10.45 – 12.45
Working Group Discussions
12.45 – 13.00
Break
13.00 – 13.30
General Discussion & Closing
13.30 –
Lunch (Restaurant Q)
7
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 micromechanical 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 (3D) 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.
11
[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.
12
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
Franz-Josef Straße 18, 8700 Leoben, Austria
‡‡
Graz University of Technology, Institute for Paper, Pulp and FiberTechnology
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
13
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.
14
Wetting and tensile deformation of single spruce wood fibres
followed by Raman microscopy
Notburga Gierlinger1*, Michaela Eder2 and Ingo Burgert2
1
Institute 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
100
TENS
STOP
TENS
STOP
100
TENS
TENS
STOP
TENS
STOP
1096
TENS
40
80
1094
H20
40
20
force [mN]
30
60
MFA [°]
force [mN]
-1
wavenumber [cm ]
80
60
1092
H20
40
1090
20
20
10
1088
0
0
0
0
200
400
time [s]
600
800
1086
0
200
400
600
800
time [s]
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).
15
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:
⎡ l
P(σ ) = 1 − exp⎢−
⎢⎣ l 0
⎛σ ⎞
⎜⎜ ⎟⎟
⎝β ⎠
α
⎤
⎥
⎥⎦
(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:
⎡ ⎛l
P(σ ) = 1 − exp⎢− ⎜⎜
⎢⎣ ⎝ l 0
⎞
⎟⎟
⎠
γ
⎛σ ⎞
⎜⎜ ⎟⎟
⎝β ⎠
α
⎤
⎥
⎥⎦
with 0 ≤ γ ≤ 1 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.
(2)
17
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.
18
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,
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
Osquars Backe 1
[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),
[email protected]
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 tensioncompression 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
Tensile strength σf (MPa)
Fibre
Young’s modulus Ef (GPa)
Spruce
663
39
Larch
708
34
Pine
730
29
Area (mm2)
0.055
0.041
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
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.
(a)
(b)
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.
29
An automated method to recognize individual fibers from threedimensional tomographic images
Arttu Miettinen*, Viivi Koivu, Tuomas Turpeinen, Jussi Timonen, and Markku
Kataja
Department of Physics
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, twistextension 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
[email protected]
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.
MSC-ratio
3.0
2.5
2.0
1.5
1.0
0
5
10
15
20
25
30
Microfibril angle
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-polypropylenecomposites
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 aftertreatment 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 woodpolypropylene-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
1
Institute for Multidisciplinary Research,
Kneza Višeslava 1
11000 Beograd, Serbia;
*[email protected]
2
Faculty 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 FTIR 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, 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
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.
(1)
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]:
α
⎛ S ⎞
⎟
⎝ S0 ⎠
σ b = σ b0 ⋅ ⎜
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
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 micromechanical 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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