Properties of cell walls prepared using supercritical fluids

1
Properties of cell walls prepared using
supercritical fluids

• Paul Callaghan (VUW),
• Robert Franich, Stefan J. Hill,
• and Roger Newman (Scion)

2

• Presentation overview
• Wood cell walls
• polymers
• water
• Fibre-saturation point
• Supercritical CO2
• Water extraction
• Wood material properties
• Summary

3
Structure of wood cell wall

H2O ?
4
Fibre-saturation point
-a chemical phenomenon at molecular/supramolecular
scales

Cells from green wood full lumens
fully-water-swollen cell walls xylem sap FSP
empty lumens fully-water-swollen cell walls

• FSP- independent of scale log/fibres
• Discrete water binding sites - OH
• Exothermic wood cell wall hydration
• a molecular chemical interaction

Stamm et al, 1935-1971 cell water as gas,
liquid, solid solution phases
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Partial specific volume of water at mc below FSP
Compression of water molecules at binding sites

1000 bar
200 bar
Stamm Seborg, 1935 Stamm, 1967
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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 Henrys
Law, the Le Chatelier Principle and the Phase
Rule. VariablesP, T, phase (gas, liquid,
supercritical)
CO2 ? P, ?1/T
CO2 H2O H2CO3 H HCO3-
H CO32-
F C P 2
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The reactants properties

Rel static permittivity Dipole moment
D Enthalpy evap kJ/mol Entropy evap J/(molK)
1.60 e0 at 0 C, 50 B
80.36 e0 at 20 C
0
1.85
15.33 at 57.5C
40.68
70.8
108.9
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Supercritical Fluids
Phase-change driving chemical change
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Supercritical CO2 wood dewatering
Comparison of oven-dried (105?C) and SCCO2
dewatered radiata pine wood
Fibre Saturation Point
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Dewatering air-drying

SCCO2 chemi-mechanical dewatering
Wood specimen mc ()
Diffusion-evaporation drying
FSP28
Dewatering drying sequence
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Practical specimen preparation
5 SCCO2 gaseous CO2 sequences

Wood specimen mc ()
Preparation time (min)
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1H NMR imaging of SCCO2 dewatering
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159?68
SCCO2 dewatering Preparation of wood specimen
with uniform mc distribution approaching
FSP Re-wetting? Further drying?
40?2
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Solid State 13C NMR Spectrum
Pinus radiata wood at 12 mc
Hemicellulose
Cellulose Lignin
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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.
• Stamms solid-solution ?

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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