Fibre Chemistry Flashcards
What layer of the fibre contains the most cellulose?
The S3 layer. it gradually reduces when moving towards the middle lamella
Roughly how much lignin in hardwoods?
21%
Roughly how much lignin in softwoods?
25%
Roughly what percent of wood are extractives? (terpenes, resin acids, fatty acids, and phenols)
2-8%
What are the 2 types of carbohydrate in wood? And what is their percentage of the wood
Cellulose 45% and hemicellulose 35%HW 25% SW
What percent of wood is cellulose?
45%
What is the function of cellulose?
To absorb mechanical force, especially tensile force
What is the function of lignin?
To absorb compressive forces, to protect against hydrophilic attacks, to act as a glue
What is the function of hemicellulose?
Act as a glue and give flexibility
What is the function of proteins?
Cell division
Where in the cell wall is the highest lignin and hemicellulose content?
The content increases gradually growing out from the S3 layer towards the middle lamella
How do you determine the degree of polymerisation (number of repeating polymer units)
Viscosity measurements
Which is harder for solvents/reagents to penetrate, the amorphous or the crystalline regions in a cellulose microfibril?
The crystalline regions are difficult to penetrate. The amorphous regions however are readily penetrated and susceptible to hydrolysis reactions.
What is the difference between pentose and hexose?
Pentose is a 5 carbon sugar whereas hexose contains 6 carbons
List the hexoses (3)
Glucose mannose galactose
List the pentoses (2)
xylose arabinose
What are the special properties of hemicellulose?
Soft and tough
Relatively hydrophilic
Soluble in alkali
More easily degraded by acids and bases than cellulose
What does hemicellulose function as?
Softening agent in cellulose fibrils and as connection between cellulose and lignin in wood. It is also a hydrophilic component which help the biological degradation of wood.
In simple - acts as flexible glue between cellulose fibrils and lignin
What is a simple way of describing hemicelluloses function
It acts as the glue between cellulose fibrils and lignin
What are the 5 monomers found in hemicellulose
glucose, mannose, galactose, xylose, arabinose
What is the function of lignin?
Give plants rigidity and act as glue to bind fibre cell walls together. Also to decrease water permeation across cell walls of xylem and make the wood more resistant to attack by microorganisms
What component is responsible for decreasing water permeation across cell walls of the xylem, giving rigidity and binding cell walls together?
Lignin
What bonds are lignin units connected by?
2/3 ether bonds. The rests carbon-carbon bonds
What type of solvent can extract extractives?
Organic solvents,
What are the main components of extractives?
Turpentine
Rosins (mixture of resin acids)
Lipids
Waxes
Lignan - product degraded from lignin
What are the objectives of lignin in wood?
Give the plants rigidity and act as a glue between fibre cell walls. It also decreases water permeation across cel walls
phen
benz
carb
Which functional groups have major influence on reactivity of lignin?
Phenolic hydroxyl, benzylic hydroxyl and carbonyl groups
Are extractives usually hydrophobic or hydrophilic?
Hydrophobic. Can be extracted using organic solvents `
What is rosin also called?
Pitch
What are positive effects of fibre swelling?
Increase in fibre flexibility.
fibres can collapse.
Improves fibre to fibre bonding during drying
What is fibre swelling influenced by?
Influenced by osmotic pressure as a dunction of fibre charge and pH
Refining can increase the swelling
How does lignin influence fibre swelling
It is hydrophobic and inhibits fibre swelling. The lignin also gives rigidity
How does hemicellulose influence fibre swelling?
Has an amorphous structure, it is hydrophilic and therefore highly swellable. The charge can influence the osmotic pressure
How does cellulose influence fibre swelling?
Has a mainly crystalline structure but is still hydrophilic, the swelling depends on the degree of polymerisation
What makes he fibre surface anionic>
Carboxyl groups (COOH). The hydroxyl groups of cellulose allow interfibre bonding
What has a high influence on paper properties (Fibre chemistry)
The wood species & climate
The pulping & bleaching method
Hemicellulose and lignin content
Cellulose characterization (DP)
Refining
Describe the molecular organisation of a cellulose microfibril
Both crystalline and amorphous regions
What is hemicellulose built from?
Five different sugars
Hexoses: glucose, mannose, galactose
Pentoses: xylose, arabinose
what are the main linkages between phenyl propane units in lignin?
Main linkages are ether bonds.
The rest are carbon to carbon bonds
Are resin canals found in hardwoods or softwoods?
Resin cannals are only found in softwoods.
They secrete resins to the central lumen
What is the purpose of vessel cells?
they are the main conducting element in hardwood species
What is the function of ray parenchyma and longitudinal parenchyma cells?
Storage
- What are the main components of wood?
Cellulose(45%). Hemicellulose(25-35%). Lignin (21-25%). Extractives (2-8%)
What are the monomers of cellulose
Glucose sugar units
Explain the molecular organization within a cellulose microfibril.
There are both crystalline and amorphous regions in cellulose microfibril. The crystalline regions are difficult to penetrate by solvents and reagents whereas the amorphous ones are readily penetrated and therefore susceptible to hydrolysis reactions.
Explain the reason of the high strength properties of cellulose.
Difference in electronegativity between hydrogen and oxygen causes hydrogen bonds to form in 3 directions.
The sum of these hydrogen bonds gives strength
What are the differences in molecular structure of hemicellulose in comparison to cellulose?
Hemicellulose is amorphous and built of different sugar monomers rather than just glucose.
Define extractives. How do you determine them?
they are hydrophobic components which can be removed with organic solvents,
