Levels of scale in study of wood structure
Wood zones
Trunk zones
Growth rings
Tree
Chemical
Microfibril
Ultrastructural
Cellular
anatomy
1
Wood Chemistry
WOOD
Holocellulose
Cellulose
Lignin(s)
Extractives
Ash
Hemicellulose(s)
2
Crystals in longitudinal parenchyma
(Côté)
Crystals in wood
rhomboidal
styloid
raphides
druses
(Kollmann and Cote)
Wood Extractives
• Pathological
• Resin acids
vs.
Fats
Physiological
Waxes
Terpenes
• Aliphatics
Flavanoids
Terpenes and terpenoids
Lignans
Phenolics
Stilbenes
5
6
*
Glucose
7
*
Cellobiose
Cellulose
1-4 glycosidic bond
8
Hemicelluloses – sugar monomers
9
*
Cellulose and Hemicellulose(s)
Cellulose
Glucose
Glucose
Glucose
Glucose
Softwood galactoglucomannan
Glucose
Mannose
Mannose
Galactose
Acetyl
Mannose
Hardwood xylan
Xylose
Xylose
Acetyl
7
Xylose
Xylose
Glucoronic
acid
10
Cellulose and Hemicellulose(s)
Cellulose
Hemicellulose (softwood)
Hemicellulose (hardwood)
Hemicelluloses vs. Cellulose
•
•
•
•
•
Additional sugar monomer types
Lower degree of polymerization (150-200)
Additional chemical functional groups
Branched chain structure
Less crystalline
12
Lignins – 3-D polymers composed of phenylpropane units with a somewhat
different composition in softwoods and hardwoods. They encrust the intercellular
space and any openings in the cell wall after the cellulose and hemicelluloses have
been deposited. Most normal softwoods contain 30%±4% lignin and hardwoods of
the temperate zone 20%±3%. Lignins are polymerization products of ….
softwoods &
hardwoods
hardwoods
phenolic
oxygen
methoxyl group
13
Lignin – inter-phenyl propane unit linkages
14
Lignin – inter-phenyl propane unit linkages
15
*
Representative structure of lignin
(Adler)
16
Another lignin
model structure!!
17
*
Cell Wall Constituents
Polymer
Cellulose
Hemicellulose(s)
Lignin(s)
Monomer(s)
Glucose
Various
Phenyl propane
monosaccharides
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
18
Chemical composition of wood
Softwood
Hardwood
Cellulose
45 – 50%
45 – 50%
Hemicellulose(s)
18 – 25%
25 – 35%
Lignin(s)
25 – 35%
20 – 25%
19
*
Ranges of scale in cell wall structure
20
Cellulose
--- Glucose ------- Glucose ------- Glucose ------- Glucose ---
Cellulose
*
Glucose vs. Mannose
OH
H
*
Glucose vs. Mannose
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.
*
Cellulose
inter-molecular
hydrogen bonds
covalent bonds
intra-molecular hydrogen bonds
*
Wood Ultrastructure - Microfibril
26
Lamella
*
True
middle
lamella
Cell Wall Layers
Primary
wall
S3
S2
S1
Lumen
Secondary wall
(Côté)
28
*
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)
29
Cell wall topochemistry
Distribution of lignin in cell walls of
hardwood fibers (darker = more lignin)
Distribution of the principle chemical components
within the various layers of the cell wall
(Panshin & de Zeeuw)
30
Lignin distribution – effects on pulping yields
Mechanical pulping
Chemical pulping
Water in cell wall
H
O
O
H
H
H
H
O
O
H O
O
H H
H
O
H
H
O
H
H
H
H
O
H
H
O
O
H
O
O
H
H
O
O
O
O
H
H
O
H
H
Microfibril angle and wood shrinkage
S2Ɵ relatively small
Leads to little longitudinal shrinkage
S2Ɵ relatively large
Leads to more longitudinal shrinkage