"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."

NOTE TAKER NEEDED

WOOD CHEMISTRY:WOOD CHEMISTRY:“What is wood made “What is wood made

of?”of?”

Wood Macroscopic StructureWood Macroscopic Structure

Outer Bark

CambiumXylem

Phloem

(inner bark)

Heartwood

Sapwood

Pith

Annual Rings

Earlywood

Latewood

Knot

Wood Microscopic StructureWood Microscopic Structure

Imagine that wood is Imagine that wood is made up of millions and made up of millions and millions of toilet paper millions of toilet paper rolls glued together. rolls glued together. These rolls are the fibers These rolls are the fibers that will make paper.that will make paper.

Chemical CompositionChemical Composition ~50% Cellulose~50% Cellulose ~25% Hemicellulose~25% Hemicellulose ~25% Lignin~25% Lignin Variable amounts of Variable amounts of

extractives extractives

3 Main Wood Chemicals3 Main Wood Chemicals

CelluloseCellulose

HemicellulosHemicellulos

eses

LigninLignin

They are all

POLYMERS

What is a polymer?What is a polymer? Polymers are made by Polymers are made by

stringing together a stringing together a bunch of little bunch of little molecules to make a molecules to make a big molecule big molecule

All plastics are All plastics are polymers polymers

Polymers can bePolymers can be linear (long strings) linear (long strings) planar (big sheets)planar (big sheets) three dimensional (like three dimensional (like

lignin)lignin) A bowling ball is one big A bowling ball is one big

three dimensional three dimensional polymerpolymer

Source: World Book Encyclopedia

THE GRADUATE

Images from D. Briggs

Hardwood vs Softwood Fibers

White Pine Red Oak

Fiber StructureFiber Structure

Lumen

Primary

WallMiddle lamella(almost all lignin)

{Secondary

Wall

Woody cells Woody cells consist of consist of several several different layersdifferent layers

The area The area between cells between cells is known as the is known as the middle lamellamiddle lamella

The lignin The lignin content lowers content lowers through the through the cell.cell.

Douglas fir fiber with spiral thickening

How is the cell wall put How is the cell wall put together?together?

Cell wall is assembled by gluing together Cell wall is assembled by gluing together a bunch of very small fibers called a bunch of very small fibers called macrofibrilmacrofibril

Same technology used to produce Same technology used to produce composite materials todaycomposite materials today The glue holding the macrofibrils together is The glue holding the macrofibrils together is

ligninlignin Macrofibrils are made up of microfibrils Macrofibrils are made up of microfibrils

which in turn are made up of cellulose and which in turn are made up of cellulose and hemicellulose polymershemicellulose polymers The glue holding all this together is ligninThe glue holding all this together is lignin

Representation of Cell Wall Representation of Cell Wall ComponentsComponents

Cellulose

Hemicelluloses

Lignin

Wood vs. Rice Krispies Wood vs. Rice Krispies TreatsTreats

Wood Ingredients: Cellulose, Wood Ingredients: Cellulose, Hemicellulose, Lignin, ExtractivesHemicellulose, Lignin, Extractives

Rice Krispies Treats Ingredients: Rice Krispies Treats Ingredients: Rice Krispies, Rice Krispies dust Rice Krispies, Rice Krispies dust (there’s ALWAYS dust in the bag), (there’s ALWAYS dust in the bag), Marshmallows, Butter, some Marshmallows, Butter, some flavoring and preservatives.flavoring and preservatives.

The Perfect RecipeThe Perfect RecipeIngredient Amount Wood Equivalent

Big Rice Krispies 1 3/4 cups Cellulose

Rice Krispies Dust 1 cup Hemicelluloses

Marshmallow 1 1/8 cup Lignin

Butter 3 tablespoons Lignin

Preservatives ~ 1-5 tablespoons Extractives

What is Cellulose?What is Cellulose?

Cellulose is straight Cellulose is straight chain polymer. In bead chain polymer. In bead terms, imagine a very terms, imagine a very very long straight string very long straight string of beads with 2 ends of beads with 2 ends and no branching points.and no branching points.

In wood, cellulose chains In wood, cellulose chains contain typically 10,000 contain typically 10,000 glucose molecules…glucose molecules…quite a long string of quite a long string of beads.beads.

Source: World Book Encyclopedia

Cellulose microfibrils

Microfibril diameter is about 1/100,000 mm

Cellulose For ChemistsCellulose For Chemists Very long straight chain polymer of glucose: Very long straight chain polymer of glucose:

approximately 10,000 in a row in wood. Cotton is approximately 10,000 in a row in wood. Cotton is nearly pure cellulose.nearly pure cellulose.

Cellulose molecules link up in bundles and bundles Cellulose molecules link up in bundles and bundles of bundles and bundles of bundles of bundles to of bundles and bundles of bundles of bundles to make fibersmake fibers

Cellulose forms tight bundles which are very Cellulose forms tight bundles which are very resistant to chemical attackresistant to chemical attack

O

O O

O

O

O

O

O

CH2OH

OHHO

OHHO

CH2OHOH

CH2OH

HO

OH

CH2OH

HO

O

Cellulose

Cellobiose Unit

What are Hemicelluloses?What are Hemicelluloses?

Hemicelluloses are also sugar polymers but Hemicelluloses are also sugar polymers but different from cellulose because they are:different from cellulose because they are: Made up glucose Made up glucose andand other sugars. other sugars. Contain some molecules other than sugars.Contain some molecules other than sugars. Branched little polymersBranched little polymers

The beads have Y’s in themThe beads have Y’s in them Much Much smallersmaller than cellulose as they are made than cellulose as they are made

up of between 50-300 sugars up of between 50-300 sugars There are lots of varieties of hemicelluloses.There are lots of varieties of hemicelluloses. Not very resistant to chemical attack – many Not very resistant to chemical attack – many

easily break down to simple sugarseasily break down to simple sugars

Hemicelluloses for Hemicelluloses for ChemistsChemists

Branched little uncolored sugar polymers (~ 50 Branched little uncolored sugar polymers (~ 50 to 300 sugar units)to 300 sugar units) Composition varies between wood speciesComposition varies between wood species

5 carbon sugars: xylose, arabinose5 carbon sugars: xylose, arabinose 6 carbon sugars: mannose, galactose, glucose6 carbon sugars: mannose, galactose, glucose Uronic Acids: galacturonic acid, glucuronic acidUronic Acids: galacturonic acid, glucuronic acid Acetyl and methoxyl groups (acetic acid & methanol)Acetyl and methoxyl groups (acetic acid & methanol)

O O

O

O

O

O

OH

OHHO

HO

HO OH

OO

O

HO OH

O

O

CO2HH3CO

OHHOH2C

O

O

OH

Cellulose/Hemicellulose Cellulose/Hemicellulose ComparisonComparison

Hemicellulose FragmentHemicellulose Fragment

Folded Cellulose FragmentFolded Cellulose Fragment

What is holding all these fibers What is holding all these fibers together in the tree?together in the tree?

LigninLignin Three dimensional polymerThree dimensional polymer No sugars in itNo sugars in it Nature’s glue – very similar to phenolic Nature’s glue – very similar to phenolic

resin used in plywood. Holds cellulose and resin used in plywood. Holds cellulose and hemicelluloses togetherhemicelluloses together

Second most plentiful natural materialSecond most plentiful natural material Must be removed or weakened to Must be removed or weakened to

separate fibers; turn wood to pulpseparate fibers; turn wood to pulp Dark in nature – especially after reacting Dark in nature – especially after reacting

with alkali – must be de-colored or with alkali – must be de-colored or removed to bleach pulpremoved to bleach pulp

Lignin for ChemistsLignin for Chemists

CH2 O

OH

OCH3

COHH

HC

CH2OH

OH CH2OHC

O

H3CO

C O

CH

CH

H

CH

CHOH2

HO

H

CH

OCH3

OH

C

OH2C

CHO

O

C

CH2OHH3C

O

O

COH

O CH

H3C

CH2OH

H

HCOH

1

2

3

4

5

6

7

H

HC CH

O

O CH

CH2O

C

OCH3

O

CHO

H2C

H3C

8

OHC CH CH2OH

CH2OH

O

O

C

OH

H3C9

10

O

HC CH

COHH2

CH2O

CH

O

OH

H3C

11

H3C

12

HO

CH2OHH3C

13

O

C

O

CH

O CH

O

H3C

H

CH3

CH

OH

O

CH

H3C

CH

H2COH

15

16

Carbohydrate

CH2OH

OH

OCH3

HC 14

H2COH

HC

CHO

17

HOCHO

O

C O CH2

H3C18

HCHO

O

H

H3C

19

O

CH

OCH

O

CH

O

COHH2

OH

OCH3

COHHCOHH2

20

H

CH

H2COH

OCH3

O

HC O

C

OCH3

CH

CH

CHO

22

21

O

H2COHCH2

CH2

H

C O

C

OCH3

24

25

26CH

28

27

O

CH2OH

H

CH3

CH

O

O

H2COH

H

H2COH

H3C

H3C

H2COH

O

CH

CH

OHC

O

O

O

H

23

COH

OCH3

Lignin has been described as 3 dimensional Lignin has been described as 3 dimensional chicken wire.chicken wire.

Picture taken from Katy’s chicken page.

Lignin for non-chemistsLignin for non-chemists

Representation of Cell Wall Representation of Cell Wall ComponentsComponents

Cellulose

Hemicelluloses

Lignin

Representation of Cell Wall Representation of Cell Wall ComponentsComponents

ExtractivesExtractives The term extractives refers to a group of unique The term extractives refers to a group of unique

chemical compounds which can be removed from plant chemical compounds which can be removed from plant materials through extraction with various solventsmaterials through extraction with various solvents

Typically these chemicals constitute only a small Typically these chemicals constitute only a small portion of the tree (<5%)portion of the tree (<5%) In some tropical species this can be as high as 25%In some tropical species this can be as high as 25%

Extractives are produced by plants for a variety of usesExtractives are produced by plants for a variety of uses The most common is protectionThe most common is protection

Extractives can cause serious problems for processingExtractives can cause serious problems for processing Pitch is a term which is often used when describing Pitch is a term which is often used when describing

some groups of extractives some groups of extractives Extractives are responsible for the characteristic color Extractives are responsible for the characteristic color

and odor of woodand odor of wood

Chemical Composition of Chemical Composition of Wood: HardwoodsWood: Hardwoods

0

10

20

30

40

50

60

%

Red Maple EnglishOak

Iroko Balsa

Cellulose*

Hemicellulose*

Lignin*

Extractives

* Data for Cellulose, Hemicellulose & Lignin on extractive free wood basis

Chemical Composition of Chemical Composition of Wood: SoftwoodsWood: Softwoods

05101520253035404550

%

Douglas Fir Redwood Yellow Pine Balsam Fir

Cellulose*Hemicellulose*Lignin*Extractives

* Data for Cellulose, Hemicellulose & Lignin on extractive free wood basis