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Marie-Pierre G. Laborie,

Deriving nanoscale information on wood/ adhesive composites with conventional polymer characterization techniques. Marie-Pierre G. Laborie, Assistant Prof., Department of Civil & Environmental Engineering, Washington State University. Outline. Problem and approach

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Marie-Pierre G. Laborie,

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  1. Deriving nanoscale information on wood/ adhesive composites with conventional polymer characterization techniques Marie-Pierre G. Laborie, Assistant Prof., Department of Civil & Environmental Engineering, Washington State University

  2. Outline • Problem and approach • Solid state nuclear magnetic resonance (NMR) • Monitor mid-kHz molecular motions • Intermolecular cross polarization experiment • Dynamic mechanical analysis (DMA) • Model a relaxation and intermolecular cooperativity • Conclusions

  3. Cellulose Lignin Hemicellulose Adhesive penetration in wood Finer and Finer Scale of Adhesive Penetration

  4. Nanometer scale morphology of the wood/ adhesive interphase ? • Phenol-formaldehyde (PF) composites • Yellow-poplar (Liriodendron tulipifera) • Low molecular weight PF resin (Mn= 270g/mol; Mw= 330 g/mol

  5. Micron Angstrom Domain size DMA TCH HT1 SolidState NMR Frequency (Hz) 10-2 1 103 Approach: molecular dynamics • Effect of phenol-formaldehyde resin on wood polymer dynamics and vice-versa

  6. 13C CP/MAS nuclear magnetic resonance - 13C CP/MAS NMR relaxations: background - Application to the wood/PF interphase

  7. Dynamics of magnetization Cross polarization (CP) T CH Abundant H spins Rare 13C spins Hz, Angstrom Spin lattice kHz, Nanometer relaxation H T r 1 Lattice

  8. 1.0 0.8 (I/Imax) 0.6 0.4 0.2 0 2 4 6 8 10 12 Contact Time (ms) Measurements of TCH andHT1r • CP experiment with variable contact time TCH HT1r

  9. Cross polarization rate (TCH) • CP: transfer of magnetization between 1H and 13C • Requirements for CP • 1H must be less than 10-20 angstroms away from 13C • 1H-13C interacting nuclei pair must be rigid (near static molecular motions)

  10. 13C, deuterated PF resin Wood H1 Intermolecular CP experiment with a 13C-perdeuterated PF resin • More effective CP in wood/PF composite compared to PF alone is evidence of intermolecular CP i.e. angstrom scale proximity between wood 1H and resin 13C

  11. Proton spin lattice relaxation (HT1r) • Motional component • Spin diffusion (static component) • In homogeneous/miscible blends (up to 20 nm phase domains) • Spin diffusion averages out molecular motion • One single value of HT1r • In phase separated blends • Spin diffusion is not efficient across phase boundaries • Several values of HT1r • Spin coupling evidences homogeneity/miscibility on the 20 nanometers scale

  12. 13C CP/MAS nuclear magnetic resonance -CP/MAS NMR relaxations: background Application to the wood/PF interphase Intermolecular CP (TCH) Mid-kHz motions & spin diffusion (HT1r)

  13. 13C-d2 formaldehyde synthesis by oxidizing 13C-d4 methanol PF synthesis from 13C-d2 formaldehyde & perdeuterated reagents (phenol-d6 etc…) Catalyst Heat Air 13CD2=O 13CD3-OD 13C-perdeuterated PF resin Schmidt et al., Holzforschung 54, (2000) 98.

  14. 13C, deuterated PF resin Wood H1 13C CP/MAS NMR of 13C-perdeuterated PF resin • Downfield shift of hydroxymethyl carbon chemical shift- H-bonding ? Laborie and Frazier, J. Materials Sci. (2006) 41,18, 6001.

  15. CP rates & molecular rigidity in PF • Carbon magnetization curves for PF methylene (left) and hydroxymethyl (right) carbons • No evidence of intermolecular CP • Different near static motions (10-20 Å) in neat state & in composite Laborie and Frazier, J. Materials Sci. (2006) 41,18, 6001.

  16. 13C CP/MAS nuclear magnetic resonance -CP/MAS NMR relaxations: background Application to the wood/PF interphase Intermolecular CP (TCH) Mid-kHz motions & spin diffusion (HT1r)

  17. 13CP/MAS NMR spectrum of a wood/PF composite • Ability to monitor the molecular dynamics, HT1r relaxations of wood polymers and PF carbons Laborie et al., J. Adhes. Sci. Techno. (2006) 20,8,729.

  18. HT1r in wood/PF composite HT1r values in ms • Resin increases the HT1r of wood polymers • In the composite, the resin HT1r is in the range of that of wood polymers • Resin alters wood mid-kilohertz motion and may be spin coupled with wood polymers Laborie et al., J. Adhes. Sci. Techno. (2006) 20,8,729.

  19. Dynamic Mechanical Analysis - Intermolecular cooperativity of the a relaxation: background Application to the wood/PF interphase

  20. c 0 (T) (T) The Alpha relaxation Loss Property Frequency Tg Temperature

  21. Ngai coupling model • * characteristic relaxation time for cooperative motion • n coupling constant • C cross-over frequency • 0 relaxation time for independent motion Ngai, J. Phys. Chem. B. (1999) 103, 5895.

  22. The Cooperativity plot Plazek and Ngai, Macromolecules (1991) 24, 1222

  23. Empirical Ngai coupling model Plazek and Ngai, Macromolecules (1991) 24, 1222

  24. Dynamic Mechanical Analysis - Intermolecular cooperativity of the a relaxation: background Application to the wood/PF interphase

  25. Submersion DMA of wood • Saturation of wood & wood/PF composites in ethylene glycol • Dual cantilever beam • Temperature scans • from 20 to 120°C • 5 frequencies (0.6 Hz to 6 Hz) Laborie et al., Holzforschung (2004) 58,129.

  26. TTSP & cooperativity for plasticized wood • Ngai coupling model describes the in situ a relaxation of lignin above Tg • For yellow-poplar n=0.19±0.04 Laborie et al., Holzforschung (2004) 58,129.

  27. Lignin in situ Tg in wood/PF composite • PF reinforces wood • Lignin in situ Tg is unchanged by PF cure in wood/PF composite Laborie et al., J. Adhes. Sci. Techno. (2006) 20, 8, 729.

  28. TTSP & cooperativity for composite • PF resin increases intermolecular cooperativity of lignin (n=0.37±0.11 vs. n=0.19±0.04) • Lignin main chain motion is constrained by PF resin Laborie et al., J. Adhes. Sci. Techno. (2006) 20, 8, 729.

  29. Summary & conclusions • Solid state NMR • Resin molecular rigidity (TCH,10-20 Å) is lower in composite • Wood mid-kHz frequency motions (<20 nm) are altered by the resin • Resin and wood polymers may be spin coupled (<20 nm) • Submersion DMA • Intermolecular cooperativity of lignin is increased by the resin • Lignin main chain/segmental relaxation is constrained by the resin

  30. Interpenetrating Network Low molecular weight PF resin Cure Wood polymers network Resin application on wood Cured wood/PF composite

  31. Conclusions • Traditional polymer characterization techniques can be used to model molecular dynamics in composites • A range of domain sizes of motion can be probed depending on the experiment frequency (nanometer level) • A variety of experiments and techniques can be useful to probe molecular motions and nanometer scale interactions (DEA, DSC, CP/MAS NMR, DMA)

  32. Acknowledgments • Prof. Charles Frazier, Virginia Tech. • Dr. Lennart Salmen, Swedish Center for Pulp and Paper. • Dr. Robert Schmidt, Dynea.

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