CW201-WOOD CHEMICAL & MECHANICAL PROPERTIES

By Nafizah bt Hassan

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.

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

- 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.

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

Problems in pulping

Gives color to paper

Require stronger chemicals

There are three monomers that make up almost all lignin found in nature

p-Coumaryl alcohol

Coniferyl alcohol

sinapyl alcohols

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.