TreeTrunk zones

Wood zones

Growth rings

Cellularanatomy

Microfibril

Chemical

Ultrastructural

Levels of scale in study of wood structure

Wood Chemistry

WOOD

Holocellulose Lignin(s) Extractives Ash

Cellulose Hemicellulose(s)

Crystals in longitudinal parenchyma

(Côté)

Crystals in wood

rhomboidal styloid raphides druses

(Kollmann and Cote)

Wood Extractives

• Pathological

vs.

Physiological

• Aliphatics

Terpenes and terpenoids

Phenolics

• Resin acids

Fats

Waxes

Terpenes

Flavanoids

Lignans

Stilbenes

Structure of monosaccharidescommonly found in the cell wall

Glucose

Glucose

Glucose

Cellobiose

1-4 glycosidic bond

Cellulose

Hemicelluloses – sugar monomers

13

Cellulose and Hemicellulose(s)

Glucose Mannose Mannose Mannose

Galactose Acetyl

Glucose Glucose Glucose Glucose

Cellulose

Xylose Xylose Xylose Xylose

Acetyl Glucoronic acid7

Hardwood xylan

Softwood galactoglucomannan

Cellulose

Hemicellulose (softwood)

Hemicellulose (hardwood)

Cellulose and Hemicellulose(s)

Hemicelluloses vs. Cellulose

• Additional sugar monomer types

• Lower degree of polymerization (150-200)

• Additional chemical functional groups

• Branched chain structure

• Less crystalline

15

Lignin – Phenyl propane unit

16

softwoods & hardwoods

hardwoods

Lignin – inter-phenyl propane unit linkages

Lignin – inter-phenyl propane unit linkages

Representative structure of lignin

(Adler)

Another ligninmodel structure!!

Cell Wall Constituents

Polymer Cellulose Hemicellulose(s) Lignin(s)

Monomer(s) Glucose Various monosaccharides

Phenyl propane

Shape Straight chain Branched chain 3-D

Order Crystalline Semi-crystalline Amorphous

% of Wood 45-50 20-35 20-35

Degree of Polymerization

10,000 150-200 50-500

Softwood Hardwood

Cellulose 45 – 50% 45 – 50%

Hemicellulose(s) 18 – 25% 25 – 35%

Lignin(s) 25 – 35% 20 – 25%

Chemical composition of wood

Ranges of scale in cell wall structure

Cellulose

--- Glucose ------- Glucose ------- Glucose ------- Glucose ---

Cellulose

Glucose vs. Mannose

Glucose vs. Mannose

H

OH

Relative sizes of atoms

Adjacent glucose units can come close enough together to permit extensive hydrogen bonding to occur.

Adjacent mannose units cannot come together as closely as glucose units and less hydrogen bonding occurs.

Glucose vs. Mannose

Cellulose

covalent bonds

intra-molecular hydrogen bonds

inter-molecular hydrogen bonds

Wood Ultrastructure - Microfibril

Wood Ultrastructure - Microfibril

Lamella

Lamella

Cell Wall Layers

True middle lamella

Primary wall Secondary wall

S1

S2

S3Lumen

Cell Wall Layers

(Côté)

Cell wall layers

Layer Lamellae % Ө Spirality Order

TML --- Variable --- --- None

P --- 5 --- --- Poor

S1 4-6 7 50-70° S + Z Good

S2 30-150 85 10-30° Z High

S3 2-4 3 60-90° S + Z Fair

(Princes Risborough Laboratory)

40

Cell wall topochemistry

(Panshin & de Zeeuw)

Distribution of the principle chemical components within the various layers of the cell wall

Distribution of lignin in cell walls of hardwood fibers (darker = more lignin)

Chemical pulpingMechanical pulping

Lignin distribution – effects on pulping yields

OH

OH

OH O

H

OH

OH

Water in cell wall

OH

OH

OH

OH

OH

OH

OH

H

OH

H

OH

H

OH

H

OH

H

OH

H

Microfibril angle and wood shrinkage

S2Ɵ relatively smallLeads to little longitudinal shrinkage

S2Ɵ relatively largeLeads to more longitudinal shrinkage