NOTE TAKER NEEDED

1. NOTE TAKER NEEDED "Disability Resources for Students (DRS) is looking for a notetaker for this class to assist a student who is unable to take complete class notes because of the effects of a disability. At least two notetakers are needed; a primary who would be able to copy his/her notes once a week, and an alternate who would be on standby as a back-up notetaker. The time commitment is minimal, but the difference it makes for the student is significant. DRS pays for the photocopying and will provide a letter of recommendation for your volunteer hours. If you are interested in volunteering, or if you have any questions, please contact DRS for more information. They are located in Schmitz Hall, room 448. You may call DRS at 543-8924 or email them at uwdss@u.washington.edu. Thank you for your consideration."

2. WOOD CHEMISTRY:“What is wood made of?”

3. Wood Macroscopic Structure Annual Rings Outer Bark Phloem (inner bark) Pith Cambium Xylem Heartwood Earlywood Knot Sapwood Latewood

4. 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. • Chemical Composition • ~50% Cellulose • ~25% Hemicellulose • ~25% Lignin • Variable amounts of extractives

5. 3 Main Wood Chemicals • Cellulose • Hemicelluloses • Lignin They are all POLYMERS

6. What is a polymer? • Polymers are made by stringing together a bunch of little molecules to make a big molecule • All plastics are polymers • Polymers can be • linear (long strings) • planar (big sheets) • three dimensional (like lignin) • A bowling ball is one big three dimensional polymer Source: World Book Encyclopedia THE GRADUATE

7. Hardwood vs Softwood Fibers White Pine Red Oak Images from D. Briggs

8. Fiber Structure • Woody cells consist of several different layers • The area between cells is known as the middle lamella • The lignin content lowers through the cell. Lumen { Secondary Wall Primary Wall Middle lamella (almost all lignin)

9. Douglas fir fiber with spiral thickening

10. How is the cell wall put together? • Cell wall is assembled by gluing together a bunch of very small fibers called macrofibril • Same technology used to produce composite materials today • The glue holding the macrofibrils together is lignin • Macrofibrils are made up of microfibrils which in turn are made up of cellulose and hemicellulose polymers • The glue holding all this together is lignin

11. Representation of Cell Wall Components Cellulose Hemicelluloses Lignin

12. Wood vs. Rice Krispies Treats • Wood Ingredients: Cellulose, Hemicellulose, Lignin, Extractives • Rice Krispies Treats Ingredients: Rice Krispies, Rice Krispies dust (there’s ALWAYS dust in the bag), Marshmallows, Butter, some flavoring and preservatives.

13. The Perfect Recipe

14. What is Cellulose? • Cellulose is straight chain polymer. In bead terms, imagine a very very long straight string of beads with 2 ends and no branching points. • In wood, cellulose chains contain typically 10,000 glucose molecules…quite a long string of beads. Source: World Book Encyclopedia

15. Cellulose microfibrils Microfibril diameter is about 1/100,000 mm

16. Cellulose For Chemists • Very long straight chain polymer of glucose: approximately 10,000 in a row in wood. Cotton is nearly pure cellulose. • Cellulose molecules link up in bundles and bundles of bundles and bundles of bundles of bundles to make fibers • Cellulose forms tight bundles which are very resistant to chemical attack

17. What are Hemicelluloses? • Hemicelluloses are also sugar polymers but different from cellulose because they are: • Made up glucose and other sugars. • Contain some molecules other than sugars. • Branched little polymers • The beads have Y’s in them • Much smaller than cellulose as they are made up of between 50-300 sugars • There are lots of varieties of hemicelluloses. • Not very resistant to chemical attack – many easily break down to simple sugars

18. Hemicelluloses for Chemists • Branched little uncolored sugar polymers (~ 50 to 300 sugar units) • Composition varies between wood species • 5 carbon sugars: xylose, arabinose • 6 carbon sugars: mannose, galactose, glucose • Uronic Acids: galacturonic acid, glucuronic acid • Acetyl and methoxyl groups (acetic acid & methanol)

19. Cellulose/Hemicellulose Comparison Folded Cellulose Fragment Hemicellulose Fragment

20. What is holding all these fibers together in the tree? • Lignin • Three dimensional polymer • No sugars in it • Nature’s glue – very similar to phenolic resin used in plywood. Holds cellulose and hemicelluloses together • Second most plentiful natural material • Must be removed or weakened to separate fibers; turn wood to pulp • Dark in nature – especially after reacting with alkali – must be de-colored or removed to bleach pulp

21. Lignin for Chemists

22. Lignin has been described as 3 dimensional chicken wire. Lignin for non-chemists Picture taken from Katy’s chicken page.

23. Representation of Cell Wall Components Cellulose Hemicelluloses Lignin

24. Representation of Cell Wall Components

25. Extractives • The term extractives refers to a group of unique chemical compounds which can be removed from plant materials through extraction with various solvents • Typically these chemicals constitute only a small portion of the tree (<5%) • In some tropical species this can be as high as 25% • Extractives are produced by plants for a variety of uses • The most common is protection • Extractives can cause serious problems for processing • Pitch is a term which is often used when describing some groups of extractives • Extractives are responsible for the characteristic color and odor of wood

26. Chemical Composition of Wood: Hardwoods * Data for Cellulose, Hemicellulose & Lignin on extractive free wood basis

27. Chemical Composition of Wood: Softwoods * Data for Cellulose, Hemicellulose & Lignin on extractive free wood basis