Wood Chemistry PSE 406

1. Wood ChemistryPSE 406 Tree & Wood Structure

2. Agenda • Tree components • Stem, crown, roots • Hardwood versus softwood • Macro wood structure • Reaction wood • Micro wood structure • Cell types • Cell wall layers

3. Why Wood Structure? • Chemical distribution is dependent upon macro and microscopic structure. • Tree species dependent • Dependent upon position in tree • Cell type dependent • Dependent upon position in the cell

4. Tree Structure I • It has been my experience that the majority of students taking wood chemistry can’t tell the difference between a hardwood and a softwood. In the next few slides I am going to present you with the layman's view of what is a tree.

5. Tree Structure II • In general, trees contain these structural components: • Stump/Roots • Stem (wood & bark) • Crown: live/dead branches, foliage (leaves/needles), flowers and fruits. • There are major chemical components which are found in all of these components. We will focus on the components found in the stem.

6. Hardwoods Trees containing leafs Typically lose foliage in winter Maple, alder, oak, Softwoods Trees containing needles Typically retains needles over winter. Pines, firs, cedars, spruce Tree Structure III

7. Tree Species Differences

8. Tree Composition 1. Values for branches, foliage, bark, and wood = % of tree above ground 2. Values for roots is a separate measurement = % of total tree

9. Macroscopic Structure Annual Rings Outer Bark (dead, protection, high extractives) Phloem (inner bark) (transportation of water and nutrients) Pith Cambium (growth, inward wood, outward bark) Xylem =wood Heartwood (support, dead, dark) Earlywood Knot Sapwood (younger, light color, living cells, transportation) Definitions in notes section Latewood

10. Macroscopic Structure (2) Heartwood Sapwood Earlywood Latewood

11. Reaction Wood This is a very poor representation of a very bent tree Tension Wood (Hardwoods) Compression Wood (Softwoods) Tension or Compression Wood Notes

12. Wood Microscopic Structure • Imagine that wood is made up of millions and millions of toilet paper rolls glued together. These rolls are the fibers that will make paper • Most often the ends of these tubes are sealed. There are small holes in the sides of the tubes to allow water to pass through

13. Microscopic Structure Resin canals (epithelium parenchyma secretes resin epithelium parenchyma secretes resin) Microscopic structure of wood (Textbook of Wood Technology, Panshin, A. J., page 118 Rays (transportation of water) Tracheid (support, water transport, softwoods), in hardwoods we have libriform fibers) Pits (wholes, transport between fibers, different typs)

14. Softwood Cells Source: Wood Chemistry, Fundamentals and Applications. Sjostrom page 7 Hardwood Cells Source: Wood Chemistry, Fundamentals and Applications. Sjostrom page 10 Hardwood & Softwood Fibers

15. Microscopic Structure W-warty layer, thin, storage of metabolites Structure of woody cell by Cote, 1967. This figure is used by almost every wood chemistry text. It can be found in Wood Chemistry, Fundamentals and Applications by Sjostrom on page 14. S (S1+S2+S3)-secondary wall, the thickest, microfibrils - opposite direction P-primary wall, very thin, random microfibrils, ML-space between cells, 70-80% lignin, glue Notes

16. Cell Cross Section Primary Secondary 1 Secondary 2 Warty Layer Secondary 3 Middle lamella

17. T/F • Earlywood: wide, thin walled cells for water transport (T/F)? • Phloem: this is where growth takes place in the stem (T/F)? • Heartwood: outer (younger) portion of the woody tissue (T/F)? • Cambium: this is the dead protective layer (T/F)?

18. T/F • Vessels: short, wide, thin-walled cells found in hardwoods (T/F)? • In hardwoods, epithelium parenchyma cells secrete resin (T/F)? • …………. are holes in the fibers which allow water to flow between fibers. • Primary Layer: this is the thickest layer of the cell (T/F)?