wood processing and products the joint forces of csiro & scion water in wood material...

Wood Processing and Products

THE JOINT FORCES OF CSIRO & SCION


Water in wood material supramolecular nano-composite

Robert Franich, Roger Newman & Stefan Hill


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


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


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


Cell wall structure and chemistry

S 1-3:

Lignocelluloselayers

P: Primary wall

ML:Lignin-richmiddle lamella

M


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


Cell wall chemistry, structure and water

30%-50% water


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


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)



Hierarchy of wood-water relationships: Tree Timber Sapwood / heartwood Earlywood / latewood Cell wall Supramolecular structure / polymers



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



Hydration layers of saccharides

Few monosaccharides form hydrates

Oligosaccharides – 3- or 4- coordinated water molecules

Jeffrey, G.A. 1992


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


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 ?


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



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



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



force

A

B

C

Conceptual supramolecular modelsWood supramolecularnano-composite

Bound water layerdispersered betweennano-compositeassemblies

Hydrogen bondscission betweenstructural watermolecules

Hydrogen bondsre-formed



Conceptual supramolecular models

Cellulose

Hemicellulose

Lignin

Water layer

Hydration layers between hemicellulose-lignin and cellulose 1 phase


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


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


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


HO

H

Cellulose polymeraggregate

Supramolecularconceptual model forgreen (wet) wood cell wallnano-composite

Hydration layer

Ligno-hemicellulosecomposite

Hydration layer


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


Wood modification exploiting Velcro mechanics chemistry

El ~ 65 GPa

Cell wall modifcation using chitosan oligomers in water


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)


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 .


Acknowledgements

Dr Kirk Torr - chemistry, spectroscopy

Dr Adya Singh - microscopy

Mr Barry Penellum - MoE measurements

wood processing and products the joint forces of csiro & scion water in wood material...

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