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Wood ChemistryPSE 406
Tree & Wood Structure
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Agenda Tree components
» Stem, crown, roots» Hardwood versus softwood
Macro wood structure» Reaction wood
Micro wood structure» Cell types» Cell wall layers
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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
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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
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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.
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Tree Structure III
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
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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
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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 ground2. Values for roots is a separate measurement = % of total tree
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Macroscopic StructureOuter Bark
CambiumXylem
Phloem(inner bark)
Heartwood
Sapwood
Pith
Annual Rings
Earlywood
Latewood
Knot
Definitions in notes section
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Reaction Wood
Tension Wood (Hardwoods)
Compression Wood (Softwoods)
Tension orCompressionWood
This is a very poor representation of a very bent tree
Notes
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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
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Microscopic Structure
Microscopic structure of wood (Textbook of Wood Technology, Panshin, A. J., page 118
Notes
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Hardwood & Softwood Fibers
Softwood Cells Source: Wood Chemistry, Fundamentals
and Applications. Sjostrom page 7
Hardwood Cells Source: Wood Chemistry, Fundamentals
and Applications. Sjostrom page 10
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Microscopic Structure
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.
Notes
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Cell Cross SectionPrimary Secondary 1
Secondary 2
Secondary 3Warty Layer
Middle lamella