Wood Processing and Products THE JOINT FORCES OF CSIRO & SCION THE JOINT FORCES OF CSIRO & SCION Water in wood material supramolecular nano- composite Robert Franich, Roger Newman & Stefan Hill
Wood Processing and Products
THE JOINT FORCES OF CSIRO & SCION
THE JOINT FORCES OF CSIRO & SCION
Water in wood material supramolecular nano-composite
Robert Franich, Roger Newman & Stefan Hill
THE JOINT FORCES OF CSIRO & SCION
Overview
Why the need to understand the structure of water in cell walls ?
Cell wall chemistry, structure
Water distribution in cell walls
Velcro mechanics of wood material
Hypothesis – water structures
Some initial results
Future applications and summary
THE JOINT FORCES OF CSIRO & SCION
Why the need to understand the structure of water in cell walls ?
Water conduction in xylem necessary for living tree.
Importance to wood utilisation:
Logging - wood volumes and weights for transportation costs
Timber drying- mass to be evaporated to a target moisture content
Material stability- dimensional and conformational change with relative humidity variation
Material durability- moisture content and wood decay
THE JOINT FORCES OF CSIRO & SCION
Radiata pine sapwood Age Green Dry kg/m3 MoE GPa MoE GPa
30 550 6.42 9.5500 5.47 8.23450 4.95 7.54
15 450 ~7
Wood moisture content and MoE property
Green MC 150-250% rangeDry equilibrium MC 12-15% rangeMC= [(Wg-Wd) / Wd] x 100
THE JOINT FORCES OF CSIRO & SCION
Cell wall structure and chemistry
S 1-3:
Lignocelluloselayers
P: Primary wall
ML:Lignin-richmiddle lamella
M
THE JOINT FORCES OF CSIRO & SCION
Cell wall chemistry, structure
Hemicellulose:Cell wall component in which1,4 –linked pyranosyl units withO4 in equatorial orientation.
Conformational homology between cellulose andhemicellulose – strongnon-covalent H-binding
Koshijima & Watanabe, 2003
THE JOINT FORCES OF CSIRO & SCION
Cell wall chemistry, structure and water
30%-50% water
THE JOINT FORCES OF CSIRO & SCION
105% 96% 94% 91% 91%168% 216% 221% 231% 223%192% 199% 207% 218% 208%165% 173% 167% 172% 123%116% 117% 117% 123% 144%
39% 39% 39% 39% 41%43% 41% 40% 40% 42%41% 45% 43% 40% 41%37% 37% 36% 37% 37%39% 39% 38% 38% 40%
Green sapwoodLarge naturalmoisture contentgradients betweenearlywood andlatewood
Processed green sapwoodUniform wood moisture content
Water distribution within wood
Stahl, M. 2004
THE JOINT FORCES OF CSIRO & SCION
1H NMR imaging of water in wood
-10000
0
10000
20000
30000
40000
50000
60000
70000
80000
0 20 40 60 80 100 120 140
wood7
wood8
wood9
wood10
Green wood200% mc
40% mc
Wood specimen transectPro
ton
den
sity
(ar
b N
MR
un
its)
THE JOINT FORCES OF CSIRO & SCION
Cell wall chemistry, structure and water
Hierarchy of wood-water relationships: Tree Timber Sapwood / heartwood Earlywood / latewood Cell wall Supramolecular structure / polymers
THE JOINT FORCES OF CSIRO & SCION
Cell wall chemistry, structure and water
I
I
Cellulose phases
I triclinic, Alternating glucose conformersregularly displaced in same direction
I monoclinicTwo conformationally distinct alternating sheetsChange H-bond pattern 2-OH and 6-OH
I and I interconvertible duringmicrofibril formation by bending
Altered H20 layer on I extends 1nm
THE JOINT FORCES OF CSIRO & SCION
Cell wall chemistry, structure and water
Hydration layers of saccharides
Few monosaccharides form hydrates
Oligosaccharides – 3- or 4- coordinated water molecules
Jeffrey, G.A. 1992
THE JOINT FORCES OF CSIRO & SCION
Dynamic structure of water
Dielectric relaxation of free water - = 8.27 ps
bound water 1ns
Water clusters Water local structure
perturbed by carbohydrates
Cole-Cole parameter from microwave dielectric measurement using time domain relectometry method
Hermida-Ramon, J.M & Larlstrom, G 2004
Jeffrey, G.A. 1992Hayashi, Y et al, 2004
THE JOINT FORCES OF CSIRO & SCION
Perturbation of water structure dynamics by carbohydrates
Represented by plot of vs
Implies a gradient in water dyanamics at polysaccharide surfaces Hayashi, Y et al, 2004
HO
H HO
HH
OHH
OH
HO
HH
OH
HO
HH
OH
HO
H HO
HH
OHH
OH
HO
HH
OH
HO
HH
OH
Conformational homology between celluloseand hemicellulose reflected in bound water ?
THE JOINT FORCES OF CSIRO & SCION
Velcro mechanics in wood
Keckes, J. et al 2003Kretschemann, D & Green, D 1996
Ductile behaviour qualitatively similar to that of metal
Stress-strain curve MFA-strain curve withsimultaneous synchrotron XRD
Wet spruce wood foil
Viscous relaxation
THE JOINT FORCES OF CSIRO & SCION
Velcro mechanics in wood
Explanatory model invoking inter-fibril Velco-like ‘stick-and-slip’ processwithin the microfibril supramolecular assembly of hemicellulose-lignin
Keckes, J. et al 2003
Critical shear stress
THE JOINT FORCES OF CSIRO & SCION
Velcro mechanics in wood
Conceptual supramolecular models
Lignin
Hemicellulose HO
H
HO
H
HO
HH
OH
HO
H
HO
H
HO
H HO
H
HO
H
HO
H
HO
H
HO
H
HO
H
HO
H
HO
H
HO
H
THE JOINT FORCES OF CSIRO & SCION
Velcro mechanics in wood
force
A
B
C
Conceptual supramolecular modelsWood supramolecularnano-composite
Bound water layerdispersered betweennano-compositeassemblies
Hydrogen bondscission betweenstructural watermolecules
Hydrogen bondsre-formed
THE JOINT FORCES OF CSIRO & SCION
Velcro mechanics in wood
Conceptual supramolecular models
Cellulose
Hemicellulose
Lignin
Water layer
Hydration layers between hemicellulose-lignin and cellulose 1 phase
THE JOINT FORCES OF CSIRO & SCION
Lignin
Cellulose
Hemicellulose
Velcro mechanics in woodWet (green) wood to dry wood conceptual model
Lignin
Cellulose
Hemicellulose
Retention of bound water layerat 12% equilibrium mc
Tethering of hemicelluloseto cellulose fibril
THE JOINT FORCES OF CSIRO & SCION
180 160 140 120 100 80 60 40 20 ppm
acetyl acetyl
methoxylignin
C1c
C1h
C4i/sC6i/s
C3,5
C2
Velcro mechanics in woodTesting hydration layer theory by NMR relaxation experiments
13C NMR spectrum of dry wood specimen
THE JOINT FORCES OF CSIRO & SCION
180 160 140 120 100 80 60 40 20 ppm
Lignin
Cellulose
Hemicellulose
Total
Fast
Slow
2.50
3.00
3.50
4.00
4.50
0 1 2 3 4 5
time (ms)
Ln
re
l in
t (s
ca
led
)
Lignin (3.4 ms)
Hemicellulose (6.9 ms)
Cellulose (13.5 ms)
Velcro mechanics in woodSpin-echo CP/MAS NMR relaxation experiments with green (wet) wood
Spin-diffusion barrier detection
T2(13C) focus on segmental motion in nuclear vicinity
THE JOINT FORCES OF CSIRO & SCION
HO
H
Cellulose polymeraggregate
Supramolecularconceptual model forgreen (wet) wood cell wallnano-composite
Hydration layer
Ligno-hemicellulosecomposite
Hydration layer
THE JOINT FORCES OF CSIRO & SCION
Role of water in secondary cell wall supramolecular assembly and wood properties
Green cell wall – 30-50 % mc cell wall elements / polymers separated by water enabling “slip and stick’ Velcro mechanics between wall elements
5-7 GPa MoE
Dry, 12% water self-organised between elements with tethering of hemicellulose to cellulose between hydration layers maximum strength and stiffness - 10-20% mc
7-9 GPa MoE
THE JOINT FORCES OF CSIRO & SCION
Wood modification exploiting Velcro mechanics chemistry
El ~ 65 GPa
Cell wall modifcation using chitosan oligomers in water
THE JOINT FORCES OF CSIRO & SCION
Secondary wall modification – enhanced modulus composite
Radiata pinelow, medium &high density specimens
Individualspecimenmodifications
4
5
6
7
8
9
10
11
12
300 400 500 600 700 800 900
Wood density (kg/m3)
Mo
E (
GP
a)
THE JOINT FORCES OF CSIRO & SCION
In summary
Cell wall supramolecular structure conceptual model invokes structural hydration layers reflecting conformational homology with cellulose and hemicellulose polymersenabling Velcro mechanics in wood.
Modification of secondary cell walls with carbohydratesusing a ‘bio-mimicry’ approach can enhance cell walland consequently bulk material properties, such as MoE.
Control of hydration structures within the wood cell wall supramolecular nano-composite might offer new 21st Capproaches to wood drying and wood modification .
THE JOINT FORCES OF CSIRO & SCION
Acknowledgements
Dr Kirk Torr - chemistry, spectroscopy
Dr Adya Singh - microscopy
Mr Barry Penellum - MoE measurements