Wood Chemistry PSE 406/Chem E 470 - University of Washington
Wood Chemistry PSE 406 Tree & Wood Structure 1 Agenda Tree components Stem, crown, roots Hardwood versus softwood Macro wood structure Reaction wood
Micro wood structure Cell types Cell wall layers 2 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
3 Tree Structure I It has been my experience that the majority of students taking wood chemistry cant 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. 4 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. 5 Tree Structure III
Softwoods Trees containing needles Typically retains needles over winter. Pines, firs, cedars, spruce Hardwoods Trees containing leafs Typically lose foliage in winter Maple, alder, oak, 6 Tree Species Differences Softwoods
Hardwoods Nomenclature Conifers/ Gymnosperms Deciduous/ Angiosperms # of Species 520 30,000 Cellulose No Difference* No Difference* Hemicellulose Majority 6 carbon Sugars Majority 5 carbon Sugars Lignin 23-33% of tree
16-25% of tree Extractives Big Differences Big Differences 7 Tree Composition Composition of Trees1 Species Branches Foliage Bark Wood Roots2 Softwood 13
8.5 10.5 66 20 Hardwood 12 5 15 68 19
1. Values for branches, foliage, bark, and wood = % of tree above ground 2. Values for roots is a separate measurement = % of total tree 8 Macroscopic Structure Annual Rings Outer Bark (dead, protection, high extractives) Phloem (inner bark) Pith (transportation of water and nutrients) Cambium
9 Macroscopic Structure (2) Heartwood Sapwood Earlywood Latewood 10 Reaction Wood This is a very poor representation of a very bent tree Tension Wood (Hardwoods) Compression Wood (Softwoods)
Notes Tension or Compression Wood 11 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 12 Microscopic Structure Resin canals (epithelium parenchyma secretes resin epithelium parenchyma secretes resin) Rays (transportation of water) Tracheid (support, water transport, softwoods), in hardwoods we have libriform fibers) Pits (wholes, transport between fibers, different typs) Microscopic structure of wood (Textbook of
Source: Wood Chemistry, Fundamentals and Applications. Sjostrom page 7 14 Microscopic Structure W-warty layer, thin, storage of metabolites 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 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. 15 Cell Cross Section Primary Secondary 1 Secondary 2 Warty Layer Secondary 3 Middle lamella 16 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)? 17 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)? 18
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