Chemistry of cell wall (ppt.) gives brief information about cell wall chemistry of wood.

1. FPU 502 WOOD PHYSICS & CHEMISTRY (2+1)
CHEMICAL COMPOSITION OF CELL WALL. CARBOHYDRATE POLYMERS
HOLO CELLULOSE,CELLULOSE, HEMI-CELLULOSE & OTHER MINOR
POLYSACCHARIDES
PRESENTER
DEVAKI M
2020565602
I M.Sc. (FOREST PRODUCTS & UTILIZATION)

2. Dry wood %
CARBON 50%
HYDROGEN 6%
O2 & trace of
inorganics
44%
TYPE CELLULOSE (%) LIGNIN (%) PENTOSANS (%)
HARDWOOD 38-49 23-30 19-26
SOFTWOOD 40-45 26-34 7-14

3. WHAT IS
HOLOCELLULOSE?
Cellulose (40-45%)
+
Hemicellulose (15-25%)
Species Holocellulose α- cellulose Pentosans Klason
lignin
Ash
Hardwood 71.7+5.7 45.4+3.5 19.3+2.2 23.0 +3.0 0.5+0.3
Softwood 64.5+4.6 43.7+2.6 9.8+2.2 28.9+2.6 0.3+0.1
65-70%
Majorly
1. D-glucose
2. D-mannose
3. D-galactose
4. D—xylose
5. L-arabinose
6. D--glucuronic
acid
Lesser amounts
1. L-rhamnose
2. D-Fucose
Rich in Hydroxyl
groups
Moisture sorption
Hydrogen bonding
Source: Adapted from Pettersen, RC .1984. The Chemistry of Solid wood, Advances in Chemistry series 20, Chapter 2 pp. 57-126, Washington, DC :ACS.
TABLE 22.1

4. CELLULOSE
 Glucan polymer of D-glucopyranose
units - β-(1 → 4)-glucosidic bonds
 Building block - cellobiose – 2 sugar unit
 Average DP of at least 9000–10,000 and
possibly as high as 15,000
Chemical structure of cellulose
Chemical structure of cellobiose

5. 1) CRYSTALLINE REGION
Most wood-derived cellulose
highly crystalline
65% crystalline regions
2) AMORPHOUS CELLULOSE- Lower packing density
The -distance of one repeating unit, that is, one cellobiose unit
is c = 10.38 Å
Packing density of cellulose↑ → crystalline regions formed
REGIONS OF CELLULOSE
Planar projection of two cellulose chains
showing some of the hydrogen bond
between cellulose chains and within a single
cellulose chain
10.38 A֯

6. TYPES ACCESSIBLE
CELLULOSE
NON-ACCESSIBLE
CELLULOSE
CRYSTALLINE Surface of crystalline Other than surface
of crystalline
NON-
CRYSTALLINE
Hemicellulose &
lignin absent
Hemicellulose &
lignin present
 Moisture sorption
 Pulping
 Chemical
modification
 Extractions
 Interactions with
microorganisms
CONCEPT OF ACCESSIBLE & NON-ACCESSIBLE

8. CELLULOSE I (NATIVE CELLULOSE)
 Layers consist of parallel chains of anhydroglucopyranose units and the chains
are held together by intermolecular hydrogen bonds.
 Also intramolecular hydrogen bonds between the atoms of adjacent glucose
residues
 Insoluble in most solvents including strong alkali
 Cellulose dissolves in strong acids - 72% sulfuric acid, 41%
hydrochloric acid, and 85% phosphoric acid but degradation occurs rapidly

9. Cellulose I
Maceration
with strong
alkali
Regeneration
(Carbon
disulfide)
Xanthate
derivative
Coverted back
to cellulose
Reprecipated
– cellulose II

10. Cellulose I
Treatment Liq. Ammonia at -80֯C
Evaporation of
ammonia
Cellulose III
Cellulose III
Alkali treatment
Cellulose II
Cellulose III
Heating – glycerol at 260֯C
Cellulose IV

11. HEMICELLULOSE
collection of polysaccharide polymers with a lower DP than cellulose (average DP of 100–200)
Containing mainly the
sugars
1. D-xylopyranose
2. D-glucopyranose
3. D-galactopyranose
4. L-arabinofuranose
5. D-mannopyranose
6. D-glucopyranosyluronic
acid
7. D-galactopyranosyluronic
acid
with minor amounts of
other sugars
Hemicelluloses usually consist of more than one type of
sugar unit and are sometimes referred to by the sugars they
contain
 Galactoglucomannan
 Arabinoglucuronoxylan
 Arabinogalactan
 Glucuronoxylan
 Glucomannan & so on
The hemicelluloses also contain acetyl- and methyl-
substituted groups
soluble in alkali and are easily hydrolyzed by acids

12. HOW HEMICELLULOSE DIFFER?
Some hemicelluloses - very large amounts when the tree is under stress
They usually contain a backbone consisting of one repeating sugar unit linked β-(1 → 4)
with branch points (1 → 2), (1 → 3), and/or (1 → 6)
“Compression wood where the wood has a higher D-galactose content
as well as a higher lignin content”
(Timell 1982)

13. Hydroxyl group at carbon
 4C- pentoses- xylose & arabinose
 6C –Hexoses-glucose, galactose, &
mannose

14. Hemicellulose
type
% in
wood
Units Molar
ratio
Linkage DP
Glucuronoxylan
15-30
β-D-Xylp
10
1 → 4
200
4-O-Me-α-D-GlupA 1 1 → 2
Acetyl 7
Glucomannan
2-5 β-D-Manp 1-2 1 → 4 200
β-D-Glup 1 1 → 4
HARDWOOD HEMICELLULOSE

16. SOFTWOOD HEMICELLULOSE
MINOR HEMICELLULOSE
 L-arabinofuranose
 D-galactopyranose
 D-glucopyranouronic
acid
 Dgalactopyroanuronic
acid

18. OTHER MINOR POLYSACCHARIDES
softwoods and hardwoods
contain small amounts of
• Pectins
• starch
• proteins

19.  Polysaccharide polymer- repeating units of D-galacturonic
acid linked α-(1 → 4)
 Membranes in the boarded pits between wood cells and
in the middle lamella
 Also found as the methyl ester
PECTIN
Degradation of Membrane by microbes
↑ Permeability of wood to water based chemicals – fire
retardants & wood preservatives
High conc. in Parenchyma
cell walls in the inner bark
Act as binder
MINOR PARTS
 L-Arabinofuranose
 D-galactopyranose

20.  Principal reserve polysaccharide in plants
 Small amount of starch can also be found in the
wood cell wall
 Starch normally occurs as granules and is
composed of D-glucopyranose units linked α- (1 → 4)
(amylose) or α-(1 → 4) with branches about every 25
glucopyranosyl units at α-(1 → 6) (amylopectin)
AMYLOSE - Helix structure in the solid state due to
the α - configuration the polymer.
AMYLOPECTIN - highly branched
STARCH

21. THANK YOU…
REFERENCE
ROGER RM. (2013) – Handbook of wood chemistry & wood composition (2nd edition).