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 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+ + CO32- F = C – P + 2

8. The reactant’s properties Rel static permittivity Dipole moment D Enthalpy evap kJ/mol Entropy evap J/(mol·K) 1.60 ε0 at 0 °C, 50 B 80.36 ε0 at 20 °C 0 1.85 15.33 at –57.5°C 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 FSP=28% 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. Stamm’s ‘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