Wood Composition and Structure
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Questions and Answers

What are the primary components of wood extractives and their significance?

The primary components are terpenes, resins, fatty acids, and phenols, which play a role in the wood's chemical properties and durability.

How does cellulose differ from hemicellulose in terms of composition?

Cellulose consists of repeating units of D-glucose linked by 1,4’-b-glycosidic linkages, while hemicellulose is made up of various sugars including glucose, mannose, and galactose.

What is the significance of the crystalline and amorphous regions in cellulose?

The crystalline region is impenetrable by solvents, providing structural integrity, while the amorphous region allows easier penetration by solvents and reagents.

How does the percentage of carbohydrates differ between hardwoods and softwoods?

<p>Hardwoods contain about 35% carbohydrates, while softwoods have around 45%.</p> Signup and view all the answers

Identify the role of lignin in wood structure.

<p>Lignin provides rigidity and resistance to decay, playing a key role in the structural support of wood.</p> Signup and view all the answers

What is the principal source of fiber for pulp and paper production?

<p>Wood, consisting of 93% virgin fiber, is the principal source of fiber for pulp and paper production.</p> Signup and view all the answers

How do softwoods and hardwoods differ in their compositions?

<p>Softwoods generally have a higher cellulose content (~45%) compared to hardwoods (~42%), while hardwoods contain more lignin (~28% vs ~20%).</p> Signup and view all the answers

What are the primary components found in the cell wall of wood?

<p>The primary components found in the cell wall of wood are cellulose, hemicellulose, and lignin.</p> Signup and view all the answers

Explain the significance of extractives in wood.

<p>Extractives are extraneous substances in wood that can be easily extracted and include resins, terpenes, and fatty acids.</p> Signup and view all the answers

What characterizes the fiber length in hardwood compared to softwood?

<p>Generally, softer woods tend to have shorter fiber lengths compared to hardwoods, which typically have longer fibers.</p> Signup and view all the answers

What role does lignin play in the structure of wood?

<p>Lignin provides a three-dimensional phenolic polymer network that strengthens the wood cell walls.</p> Signup and view all the answers

How does the age of a wood plant affect its chemical composition?

<p>As a wood plant matures, its chemical composition skews towards a higher percentage of cellulose, hemicellulose, and lignin.</p> Signup and view all the answers

What are the differences in the types of trees classified as softwoods and hardwoods?

<p>Softwoods come from gymnosperms, typically needle-leafed trees, while hardwoods come from angiosperms, usually broad-leafed trees.</p> Signup and view all the answers

What are the distinguishing features of Fischer projections compared to Haworth projections?

<p>Fischer projections represent the linear form of sugars, while Haworth projections depict the cyclic forms, emphasizing ring structure.</p> Signup and view all the answers

What is the significance of the D-configuration in D-glyceraldehyde and D-glucose?

<p>The D-configuration indicates that the hydroxyl (-OH) group on the highest numbered chiral carbon is on the right in Fischer projections.</p> Signup and view all the answers

Describe the difference between alpha (α) and beta (β) anomers in D-glucose.

<p>In α-D-glucose, the hydroxyl group on the anomeric carbon is oriented down, while in β-D-glucose, it is oriented up.</p> Signup and view all the answers

What is the relationship between hemiacetals and acetals in carbohydrate chemistry?

<p>Hemiacetals form when a carbonyl reacts with an alcohol, while acetals result when a second alcohol reacts with a hemiacetal.</p> Signup and view all the answers

Explain the role of glycosidic bonds in the formation of starch and glycogen.

<p>Glycosidic bonds link monosaccharides in chains, specifically through 1,4'-α-glycosidic linkages in starch and glycogen.</p> Signup and view all the answers

What contributes to the rigidity of cellulose at a molecular level?

<p>Cellulose consists of long chains of β-D-glucose molecules linked by 1,4'-β-glycosidic bonds, forming stiff, rod-like structures.</p> Signup and view all the answers

How does mutarotation affect the behavior of α-D-glucose and β-D-glucose in solution?

<p>Mutarotation involves the interconversion between α and β forms in solution, resulting in a dynamic equilibrium.</p> Signup and view all the answers

What is the significance of carbon numbering in cyclic forms of monosaccharides?

<p>Carbon numbering in cyclic sugars is crucial for identifying the anomeric carbon and determining specific chemical reactions.</p> Signup and view all the answers

What structural characteristics allow starch and glycogen to be effective energy storage molecules?

<p>Starch and glycogen have branched structures with multiple 1,4' and 1,6' linkages, facilitating quick energy release and solubility.</p> Signup and view all the answers

Describe the importance of chirality in monosaccharide structures.

<p>Chirality in monosaccharides results in different spatial arrangements of atoms, leading to distinct properties and biological activities.</p> Signup and view all the answers

Flashcards

Lignin

A major component of wood, a complex polymer composed of aromatic rings (phenol units) linked by various bonds.

Cellulose

The most abundant organic compound on Earth, a linear polymer consisting of glucose units linked by glycosidic bonds. This structure forms strong fibers, critical for plant support.

Hemicellulose

A complex mixture of polysaccharides consisting of glucose, mannose, galactose, xylose, and arabinose. It is highly branched, making it more easily digestible than cellulose.

Crystalline regions of cellulose

Regions of the cell wall that are highly ordered and densely packed with molecules, making them resistant to water and chemicals.

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Amorphous regions of cellulose

Regions of the cell wall where molecules are less ordered, making them more accessible to solvents and other reagents.

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What is the main source of wood fiber?

Wood is primarily composed of virgin fibers, mainly sourced from trees, with a small percentage derived from non-wood sources such as bamboo and straw.

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What type of wood is associated with coniferous trees?

This type of wood, often referred to as softwood, comes from coniferous trees, like pine, fir, or spruce, typically characterized by needle-shaped leaves.

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What type of wood is associated with deciduous trees?

This type of wood, often called hardwood, comes from deciduous trees like oak, maple, or birch, known for their broad leaves.

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What are the three main components of a plant's cell wall?

The structure of a plant's cell wall is made up of three main components: cellulose, hemicellulose, and lignin. Each component contributes to the cell wall's strength and properties.

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What is the main component in the cell wall that gives strength to wood?

This component of the plant cell wall, a long chain molecule, provides structural integrity and strength.

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What component in the cell wall acts as a glue to bind the cellulose fibers together?

This component of the cell wall, a branched short chain molecule, acts as a glue, connecting the cellulose fibers and providing more structural support.

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What component in the cell wall provides rigidity and resistance to decay?

A three-dimensional phenolic polymer network, this component in the cell wall provides rigidity and resistance to decay. It's essentially the 'hardening agent' for wood.

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What are extractives in wood and how are they extracted?

These substances, extracted from wood with neutral organic solvents, include resins, fatty acids, and terpenes, and contribute to the unique properties of different types of wood.

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Fischer projection

Linear representation of monosaccharides where the carbon chain is vertical and chiral centers are indicated by horizontal lines.

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Haworth projection

Cyclic form of monosaccharides where the ring is drawn as a hexagon or pentagon.

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Mutarotation

The ability of a sugar to exist in both cyclic forms, alpha and beta, due to the ring opening and reclosing.

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D-sugar

A sugar with a hydroxyl group on the carbon furthest from the carbonyl group, on the right side in the Fischer projection.

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L-sugar

A sugar with a hydroxyl group on the carbon furthest from the carbonyl group, on the left side in the Fischer projection.

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Cis glycosidic bond

A type of glycosidic bond where the linkage is on the same side of the ring.

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Trans glycosidic bond

A type of glycosidic bond where the linkage is on opposite sides of the ring.

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Disaccharide

The molecule formed by joining two monosaccharides by a glycosidic bond.

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Starch

A polysaccharide made of glucose units linked by 1,4-alpha-glycosidic bonds with branching.

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Study Notes

Wood Composition

  • Wood = 93% of global virgin fiber supply, primarily for pulp and paper
  • 7% of fiber sources are non-wood, including bamboo, bagasse, cereal straw, cotton, linen, jute, hemp, abaca, and sisal, plus synthetic fibers
  • Cell walls consist of cellulose and other support polymers
  • Polymer chemistry specializes the simple cell structure of xylem, phloem, collenchyma, sclerenchyma, and parenchyma, amongst others

Wood Types

  • Softwoods = Conifers/Gymnosperms, needle-leafed
  • Hardwoods = Deciduous or Evergreen Angiosperms, broad-leafed

Wood Structure

  • Sapwood
  • Heartwood
  • Dead Bark
  • Live Bark
  • Cambium Layer
  • Growth Rings
  • The Pith
  • Medullary Rays

Average Composition of Softwood and Hardwood

  • Hardwood:
    • 42% Cellulose (long chain molecules, no branching, mainly skeletal polysaccharides)
    • 27% Hemicellulose (branched short chain molecules, mainly matrix polysaccharides)
    • 28% Lignin (three-dimensional phenolic polymer network)
    • 3% Extractives (extraneous substances extractable by neutral organic solvents or steam)
  • Softwood:
    • 45% Cellulose
    • 30% Hemicellulose
    • 20% Lignin
    • 5% Extractives

Softwood vs Hardwood

  • Average fiber length differs (softwood typically having a longer average fiber length)
  • Chemical composition of wood (cellulose, hemicellulose, lignin, pectin, resins, waxes, fatty and fixed oils, cyclitols, tannins, mucilage, and alkaloids) skews toward cellulose, hemicellulose, and lignin in mature woody plants
  • Components vary between different woody plants

Wood Composition Breakdown

  • Cell wall substances: Insoluble in neutral organic solvents or non-volatile with steam
  • Lignin: 21% in hardwoods, 25% in softwoods
  • Carbohydrates: 35% hardwoods, 25% softwoods
  • Cellulose: 45%, composed of glucose units
  • Hemicellulose: Consisting of glucose, mannose, galactose, xylose, and arabinose

Cellulose

  • Cellulose is (C₆H₁₀O₅)ₙ
  • Polysaccharide of repeating D-glucose units joined by 1,4′-β-glycosidic linkages
  • Chains are exclusively linear, encouraging many intra and intermolecular interactions to form a structural polysaccharide of plants
  • Two regions exist within cellulose: crystalline (impenetrable by solvents) and amorphous (easily penetrated by solvents and reagents)

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Related Documents

Pulp and Paper 1b PDF

Description

This quiz explores the composition, types, and structure of wood, highlighting the differences between hardwoods and softwoods. It covers the intricate details of wood fiber sources, cell wall composition, and various wood components. Test your knowledge on the essential aspects of wood in the context of pulp and paper production.

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