Properties of cell walls prepared using supercritical fluids - PowerPoint PPT Presentation

1 / 19
About This Presentation
Title:

Properties of cell walls prepared using supercritical fluids

Description:

Title: Wood / Water Relationships in Pinus radiata Author: Stefan J. Hill Last modified by: Information Technology Created Date: 3/20/2006 1:35:12 AM – PowerPoint PPT presentation

Number of Views:64
Avg rating:3.0/5.0
Slides: 20
Provided by: StefanJ152
Learn more at: https://www.iaws-web.org
Category:

less

Transcript and Presenter's Notes

Title: 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
5
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
6
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

7
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
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
9
Supercritical Fluids
Phase-change driving chemical change
10
Supercritical CO2 wood dewatering
Comparison of oven-dried (105?C) and SCCO2
dewatered radiata pine wood
Fibre Saturation Point
11
Dewatering air-drying

SCCO2 chemi-mechanical dewatering
Wood specimen mc ()
Diffusion-evaporation drying
FSP28
Dewatering drying sequence
12
Practical 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
15
Solid State 13C NMR Spectrum
Pinus radiata wood at 12 mc
Hemicellulose
Cellulose Lignin
16
T1?(H) Nutation-Diffusion NMR

Lignin Cellulose Hemicellulose Lignin
T1?(H) (ms)
17
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 ?

18
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

19
Acknowledgements
  • Hank Kroese, Suzanne Gallagher,
  • Bernard Dawson
    Meeta Patel
  • FRST Wood Products for the Future
  • Contract C04X0205
Write a Comment
User Comments (0)
About PowerShow.com