Tree Trunk zones Wood zones Growth rings Cellular anatomy Microfibril Chemical Ultrastructural Levels of scale in study of wood structure

Wood Chemistry WOOD Holocellulose CelluloseHemicellulose(s) Lignin(s)ExtractivesAsh

Crystals in longitudinal parenchyma (Côté)

Crystals in wood rhomboidalstyloidraphidesdruses (Kollmann and Cote)

Wood Extractives Pathological vs. Physiological Aliphatics Terpenes and terpenoids Phenolics Resin acids Fats Waxes Terpenes Flavanoids Lignans Stilbenes

Structure of monosaccharides commonly found in the cell wall

Glucose

Cellobiose

1-4 glycosidic bond Cellulose

Hemicelluloses – sugar monomers

13 Cellulose and Hemicellulose(s) Glucose Mannose Mannose Mannose Galactose Acetyl Glucose Glucose Cellulose Xylose Xylose Xylose Xylose Acetyl Glucoronic acid 7 Hardwood xylan Softwood galactoglucomannan

Cellulose Hemicellulose (softwood) Hemicellulose (hardwood) Cellulose and Hemicellulose(s)

Hemicelluloses vs. Cellulose Additional sugar monomer types Lower degree of polymerization ( ) Additional chemical functional groups Branched chain structure Less crystalline 15

Lignin – Phenyl propane unit 16

softwoods & hardwoods hardwoods

Lignin – inter-phenyl propane unit linkages

Representative structure of lignin (Adler)

Another lignin model structure!!

Cell Wall Constituents PolymerCelluloseHemicellulose(s)Lignin(s) Monomer(s)GlucoseVarious monosaccharides Phenyl propane ShapeStraight chainBranched chain3-D OrderCrystallineSemi-crystallineAmorphous % of Wood Degree of Polymerization 10,

SoftwoodHardwood Cellulose 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

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

Lamella

Cell Wall Layers True middle lamella Primary wall Secondary wall S1 S2 S3 Lumen

Cell Wall Layers (Côté)

Cell wall layers LayerLamellae%ӨSpiralityOrder TML---Variable--- None P---5 Poor S °S + ZGood S °ZHigh S °S + ZFair (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

O H O H O H O H O H O H Water in cell wall O H O H O H O H O H O H O H H O H H O H H O H H O H H O H H

Microfibril angle and wood shrinkage S 2 Ɵ relatively small Leads to little longitudinal shrinkage S 2 Ɵ relatively large Leads to more longitudinal shrinkage