Wood Chemistry PSE 406

1
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

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 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.

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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

• 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,

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Tree Species Differences
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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
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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
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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

13
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 Wood
  Technology, Panshin, A. J., page 118

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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
W-warty layer, thin, storage of metabolites
S (S1S2S3)-secondary wall, the thickest,
microfibrils - opposite direction
P-primary wall, very thin, random microfibrils,
ML-space between cells, 70-80 lignin, glue

• 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 Section
Primary
Secondary 1
Secondary 2
Warty Layer
Secondary 3
Middle lamella
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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)?

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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)?