Wood Chemistry PSE 406 Tree Wood Structure 1

Wood Chemistry PSE 406 Tree & Wood Structure 1

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

Why Wood Structure? l 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 l 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. 4

Tree Structure II l In general, trees contain these structural components: » Stump/Roots » Stem (wood & bark) » Crown: live/dead branches, foliage (leaves/needles), flowers and fruits. l 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 l Softwoods » Trees containing needles » Typically retains needles over winter. » Pines, firs, cedars, spruce l Hardwoods » Trees containing leafs » Typically lose foliage in winter » Maple, alder, oak, 6

Tree Species Differences 7

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 8

Macroscopic Structure Annual Rings Outer Bark (dead, protection, high extractives) Phloem (inner bark) Pith (transportation of water and nutrients) Cambium Xylem =wood Heartwood (support, dead, dark) Knot (growth, inward wood, outward bark) Earlywood Sapwood (younger, light color, living cells, transportation) Definitions in notes section Latewood 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 l l 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) 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 13

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

Microscopic Structure W-warty layer, thin, storage of metabolites S (S 1+S 2+S 3)-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 l l 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 l l 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