Lignin

prepared by: nafizah hassan, politeknik shah alam, malaysia. cw201

1. CW201-WOOD CHEMICAL & MECHANICAL PROPERTIES
By Nafizah bt Hassan

2. Lignin is a complex chemical compound most
commonly derived from wood, and an integral part of
the secondary cell walls of plants and some algae
A set of non-sugar molecules acting like a glue to hold
the fiber together
Lignin is chemically bound to carbohydrate materials
and occurs throughout the cell wall, being deposited
between and within microfibrils during and after the
wall - thickening process.

3. Lignin fills the spaces in the cell wall between
cellulose, hemicellulose, and pectin components,
especially in tracheids and xylem. It is covalently
linked to hemicellulose and thereby crosslinks
different plant polysaccharides, conferring
mechanical strength to the cell wall and by extension
the plant as a whole

6. -Adhesive of wood
-binds the fibres
-provides rigidity and toxicity to the wood
-Lignin is one of the most slowly decomposing
components of dead vegetation, contributing a major
fraction of the material that becomes humus as it
decomposes.

7. Stable material except when treated with Strong alkali at elevated
temperature
Stabil in Acid
Oxidising agents
Mainly located in middle lamella
Structure of lignin is complex. The most studied are those of
softwood lignin – less complex and variability

8. Problems in pulping
Gives color to paper
Require stronger chemicals

9. There are three monomers that make up almost all
lignin found in nature
p-Coumaryl alcohol
Coniferyl alcohol
sinapyl alcohols

11. p-Coumaryl alcohol is a minor component of grass
and forage type lignins.
Coniferyl alcohol is the predominant lignin
monomer found in softwoods (hence the name).
Both coniferyl and sinapyl alcohols are the
building blocks of hardwood lignin.