Lecture Notes: Cellulose

Introduction

• Cellulose: An organic compound with formula (C6H10O5)n.
• Structure: Linear chain of D-glucose units, linked by (1→4) glycosidic bonds.
• Abundance: Most plentiful organic polymer on Earth.
• Sources:
  • Cotton fiber: 90% cellulose.
  • Wood: 40-50% cellulose.
  • Dried hemp: ~57% cellulose.

Properties

• Chemical Formula: (C6H10O5)n.
• Molar Mass: 162.1406 g/mol per glucose unit.
• Appearance: White powder.
• Density: 1.5 g/cm3.
• Melting Point: Decomposes at 260-270°C.
• Solubility: Insoluble in water.
• Thermochemistry:
  • Std enthalpy of formation: 963 kJ/mol.
  • Std enthalpy of combustion: -2828 kJ/mol.

Uses

• Industrial: Mainly from wood pulp and cotton.
• Products:
  • Paper, paperboard, cellophane, rayon.
  • Biofuels (cellulosic ethanol).

Biological Role

• Plant Cell Walls: Integral structural component.
• Animal Digestion:
  • Ruminants/Termites: Digest with symbiotic microorganisms.
  • Humans: Acts as dietary fiber, aiding in digestion.

History

• Discovered: 1838 by Anselme Payen.
• Development:
  • 1870: First thermoplastic polymer, celluloid.
  • 1890s: Rayon production.
  • 1912: Invention of cellophane.

Structure and Properties

• Microscopic Structure: No taste, odorless, hydrophilic, chiral, biodegradable.
• Polymer Structure: Straight chain, no coiling or branching.
• Hydrogen Bonding: Forms microfibrils; contributes to tensile strength.

Types of Cellulose

• Natural (Cellulose I): Bacterial and higher plants, enriched in cellulose I and I.
• Regenerated (Cellulose II): Irreversible from cellulose I.
• Chain Length:
  • Wood pulp: 300-1700 glucose units.
  • Cotton/Bacterial: 800-10,000 units.

Applications

• Nanocellulose: Technological interest, used in hydrogels, aerogels, and nanocomposites.
• Biosynthesis: Synthesized at plasma membrane by rosette terminal complexes.
• Cellulolysis: Breakdown into glucose or cellodextrins, difficult due to strong bonding.

Regenerated Cellulose

• Process: Solubilizing cellulose for products like viscose.
• Applications: Textiles, medical devices, artificial membranes.

Cellulose Derivatives

• Ester and Ether Derivatives: Modified for various industrial applications.

Commercial Applications

• Paper Products: Major constituent.
• Fibers: Main ingredient of textiles (cotton, synthetics).
• Food: Additive for texture and bulk.
• Building Material: Eco-friendly alternatives.
• Pharmaceuticals: Used as stabilizers and thickeners.