properties of cell walls prepared using supercritical fluids
DESCRIPTION
Properties of cell walls prepared using supercritical fluids. Paul Callaghan (VUW), Robert Franich, Stefan J. Hill, and Roger Newman (Scion). Presentation overview: Wood cell walls polymers water Fibre-saturation point Supercritical CO 2 Water extraction Wood material properties - PowerPoint PPT PresentationTRANSCRIPT
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Properties of cell walls prepared using supercritical fluids
Paul Callaghan (VUW), Robert Franich, Stefan J. Hill, and Roger Newman (Scion)
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Presentation overview:
•Wood cell wallspolymerswater
•Fibre-saturation point
•Supercritical CO2
•Water extraction
•Wood material properties
•Summary
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Structure of wood cell wall
H2O ?
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Fibre-saturation point
Stamm et al, 1935-1971: cell water as gas, liquid, ‘solid solution’ phases
Cells from green wood –full lumens & fully-water-swollencell walls – xylem sap
FSP –empty lumens & fully-water-swollencell walls
-a chemical phenomenon at molecular/supramolecular scales
•FSP- independent of scale –log/fibres•Discrete water binding sites - OH•Exothermic wood cell wall hydration – a molecular chemical interaction
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Partial specific volume of water at %mc below FSP
Stamm & Seborg, 1935; Stamm, 1967
‘Compression’ of water molecules at binding sites
200 bar
1000 bar
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Wood material dynamics
Wood at variable moisture content – dimensional, conformational & MoE change
Water an integral part of the cell wall supramolecular cellulose-hemicellulose-lignin nanocomposite dynamics-
- ‘Velcro’ mechanics
Where is water located and how structured?
Difficulty in preparing wood specimens for study of FSP &material dynamics – heating, solvents, azeotropes, critical-point, high-pressure
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Supercritical CO2 water extraction
Theory: Physical-chemical interaction of cell water and carbon dioxide according to Henry’s Law, the Le Chatelier Principle and the Phase Rule.
Variables:P, T, phase (gas, liquid, supercritical)
[CO2] P, 1/T
CO2 + H2O H2CO3 H+ + HCO3- H+ + CO3
2-
F = C – P + 2
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The reactant’s properties
80.36 ε0 at 20 °C
40.68
108.9
1.85
Rel static permittivity
Dipole moment D
Enthalpy evap kJ/mol
Entropy evap J/(mol·K)
1.60 ε0 at 0 °C, 50 B
0
15.33 at –57.5°C
70.8
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Supercritical Fluids
Phase-changedriving chemicalchange
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Supercritical CO2 wood dewatering
Fibre SaturationPoint
Comparison of oven-dried (105C) and
SCCO2 dewatered radiata pine wood
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Dewatering & air-drying
0
50
100
150
200
250
1 3 5 7 9 11 13 15 17 19 21 23 25
y = -33.837x + 233.2
y = -1.4143x + 36.781
FSP=28%
Dewatering & drying sequence
Wo
od
sp
ecim
en m
c (%
)
SCCO2 chemi-mechanical dewatering
Diffusion-evaporation drying
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Practical specimen preparation
Wo
od
sp
ecim
en m
c (%
)
Preparation time (min)
0
50
100
150
200
250
0 2 4 6 8 10 12
5 SCCO2 – gaseous CO2 sequences
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1H NMR imaging of SCCO2 dewatering
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Cycle
105% 96% 94% 91% 91% mean0 168% 216% 221% 231% 223% 159%
192% 199% 207% 218% 208%165% 173% 167% 172% 123%116% 117% 117% 123% 144%
107% 146% 151% 161% 165% mean1 103% 101% 99% 91% 89% 142%
155% 167% 165% 162% 157%185% 200% 207% 209% 199%105% 116% 113% 103% 94%
91% 96% 94% 86% 83% mean2 143% 151% 157% 152% 138% 113%
82% 86% 103% 122% 84%161% 111% 75% 73% 89%124% 142% 141% 131% 105%
44% 43% 43% 43% 48% mean3 69% 72% 75% 81% 70% 59%
72% 81% 91% 95% 76%46% 50% 52% 54% 48%43% 42% 43% 44% 49%
45% 38% 36% 40% 46% mean4 50% 46% 37% 36% 38% 43%
44% 53% 56% 40% 38%39% 39% 47% 54% 48%45% 38% 38% 40% 46%
39% 39% 39% 39% 41% mean5 43% 41% 40% 40% 42% 40%
41% 45% 43% 40% 41%37% 37% 36% 37% 37%39% 39% 38% 38% 40%
SCCO2 dewatering
Preparation of woodspecimen with uniform mc distributionapproaching FSP
Re-wetting?
Further drying?
15968
402
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Solid State 13C NMR Spectrum
O
HO
HO
OH
OH
OH
C1
C2
C3
C4
C5
C6
Pinus radiata wood at 12% mc
180 160 140 120 100 80 60 40 20 ppm
acetyl acetyl
methoxylignin
C1c
C1h
C4i/sC6i/s
C3,5
C2
Cellulose LigninHemicellulose
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T1(H) Nutation-Diffusion NMR
Lignin
Cellulose
Hemicellulose
Lignin
T1
(H)
(ms)
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Water in cell wall at FSP
NMR evidence of a water layer between the cellulose aggregate -phase and the matrix
in the supramolecular nanocomposite of green wood.
Stamm’s ‘solid-solution’ ?Cellulose
Hemicellulose
Lignin
Water layer
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SCCO2 dewatering process - summary
Reaction of lumen water with SCCO2
with reversal of chemistry in gas phase
Bound water bond strength higher than enthalpy of SCCO2 reaction – no change
Wood material derived approaching FSP from green
Material suitable for wood-water dynamics & cell wall studies – Green to FSP & below
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Acknowledgements
Hank Kroese, Suzanne Gallagher,
Bernard Dawson & Meeta Patel
FRST – ‘Wood Products for the Future’
Contract C04X0205