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Understanding Wood Structure Scales: Levels, Composition, and Chemistry

Explore the intricate levels of scale in wood structure, from growth rings to cellular anatomy and ultrastructural components. Learn about the chemical composition of wood zones and the role of various compounds such as lignin, cellulose, and extractives in wood chemistry. Understand the implications of wood ultrastructure on properties like shrinkage and pulping yields.

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Understanding Wood Structure Scales: Levels, Composition, and Chemistry

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  1. Levels of scale in study of wood structure Wood zones Trunk zones Growth rings Tree Chemical Cellular anatomy Microfibril Ultrastructural

  2. Wood Chemistry

  3. Crystals in longitudinal parenchyma (Côté)

  4. Crystals in wood rhomboidal styloid raphides druses (Kollmann and Cote)

  5. Wood Extractives • Pathological vs.Physiological • AliphaticsTerpenes and terpenoidsPhenolics • Resin acidsFatsWaxesTerpenesFlavanoidsLignansStilbenes

  6. Structure of monosaccharidescommonly found in the cell wall

  7. Glucose

  8. Glucose

  9. Glucose

  10. Cellobiose

  11. 1-4 glycosidic bond Cellulose

  12. Hemicelluloses – sugar monomers

  13. Cellulose Glucose Glucose Glucose Glucose Xylose Xylose Xylose Xylose Acetyl Glucoronic acid 7 Cellulose and Hemicellulose(s) Softwood galactoglucomannan Glucose Mannose Mannose Mannose Galactose Acetyl Hardwood xylan

  14. Cellulose and Hemicellulose(s) Cellulose Hemicellulose (softwood) Hemicellulose (hardwood)

  15. Hemicelluloses vs. Cellulose • Additional sugar monomer types • Lower degree of polymerization (150-200) • Additional chemical functional groups • Branched chain structure • Less crystalline

  16. Lignin – Phenyl propane unit

  17. softwoods & hardwoods hardwoods

  18. Lignin – inter-phenyl propane unit linkages

  19. Lignin – inter-phenyl propane unit linkages

  20. Representative structure of lignin (Adler)

  21. Another ligninmodel structure!!

  22. Cell Wall Constituents

  23. Chemical composition of wood

  24. Ranges of scale in cell wall structure

  25. Cellulose --- Glucose ------- Glucose ------- Glucose ------- Glucose ---

  26. Cellulose

  27. Glucose vs. Mannose

  28. Glucose vs. Mannose OH H

  29. Relative sizes of atoms

  30. Glucose vs. Mannose Adjacent glucose units can come close enough together to permit extensive hydrogen bonding to occur. Adjacent mannose units cannot come together as closely as glucose units and less hydrogen bonding occurs.

  31. Cellulose inter-molecular hydrogen bonds covalent bonds intra-molecular hydrogen bonds

  32. Wood Ultrastructure - Microfibril

  33. Wood Ultrastructure - Microfibril

  34. Lamella

  35. Lamella

  36. Cell Wall Layers Lumen S3 Primary wall True middle lamella S2 Secondary wall S1

  37. Cell Wall Layers (Côté)

  38. Cell wall layers (Princes Risborough Laboratory)

  39. Cell wall topochemistry Distribution of lignin in cell walls of hardwood fibers (darker = more lignin) Distribution of the principle chemical components within the various layers of the cell wall (Panshin & de Zeeuw)

  40. Lignin distribution – effects on pulping yields Mechanical pulping Chemical pulping

  41. Water in cell wall H O H H H H O O O O H O H H H O H H H O O O H O H O H H O H H H H H O O O O O H H H

  42. Microfibril angle and wood shrinkage S2Ɵ relatively largeLeads to more longitudinal shrinkage S2Ɵ relatively smallLeads to little longitudinal shrinkage

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