Title: Properties of cell walls prepared using supercritical fluids
1Properties 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
3Structure of wood cell wall
H2O ?
4Fibre-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
5Partial specific volume of water at mc below FSP
Compression of water molecules at binding sites
1000 bar
200 bar
Stamm Seborg, 1935 Stamm, 1967
6Wood 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
7Supercritical 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
8 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
9Supercritical Fluids
Phase-change driving chemical change
10Supercritical CO2 wood dewatering
Comparison of oven-dried (105?C) and SCCO2
dewatered radiata pine wood
Fibre Saturation Point
11Dewatering air-drying
SCCO2 chemi-mechanical dewatering
Wood specimen mc ()
Diffusion-evaporation drying
FSP28
Dewatering drying sequence
12Practical specimen preparation
5 SCCO2 gaseous CO2 sequences
Wood specimen mc ()
Preparation time (min)
13 1H NMR imaging of SCCO2 dewatering
14 159?68
SCCO2 dewatering Preparation of wood specimen
with uniform mc distribution approaching
FSP Re-wetting? Further drying?
40?2
15Solid State 13C NMR Spectrum
Pinus radiata wood at 12 mc
Hemicellulose
Cellulose Lignin
16T1?(H) Nutation-Diffusion NMR
Lignin Cellulose Hemicellulose Lignin
T1?(H) (ms)
17Water 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 ?
18SCCO2 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
19Acknowledgements
- Hank Kroese, Suzanne Gallagher,
- Bernard Dawson
Meeta Patel - FRST Wood Products for the Future
- Contract C04X0205