Rubber and Fibers
Objectives
- Know the difference between natural and synthetic rubber
- Understand the purpose of vulcanization
- Classify natural, semi-synthetic, and synthetic fibers
Rubber
Natural rubber: addition polymer of isoprene (C₅H₈) — polyisoprene with cis configuration.
Elastic but sensitive to heat and solvents.
Vulcanization: heating natural rubber with sulfur S → sulfur cross-links form between chains → improved elasticity and durability.
| Type | Monomer | Features |
|---|---|---|
| Natural rubber | Isoprene | Elastic, low heat resistance |
| SBR (styrene-butadiene) | Styrene + butadiene | Tire use, abrasion resistant |
| Chloroprene rubber | Chloroprene | Oil/weather resistant |
| Silicone rubber | Siloxane | Heat resistant, medical use |
Types of rubber
Fibers
| Category | Examples | Source/Features |
|---|---|---|
| Natural (plant) | Cotton, linen | Cellulose-based, absorbent |
| Natural (animal) | Silk, wool | Protein-based, insulating |
| Regenerated | Rayon, cupro | Dissolved & re-spun cellulose |
| Semi-synthetic | Acetate | Chemically modified cellulose |
| Synthetic | Nylon, PET, acrylic | Petroleum-based, condensation/addition |
Classification of fibers
Nylon 6,6 (condensation):
Hexamethylenediamine + adipic acid → polyamide + H₂O
PET (condensation):
Terephthalic acid + ethylene glycol → polyester + H₂O
Acrylic fiber (addition):
Addition polymerization of acrylonitrile CH₂=CHCN
Check Your Understanding
Q1 What is the process of heating rubber with sulfur called?
Q2 What category of fiber is rayon?
Q3 How is Nylon 6,6 polymerized?
Exercises
Q1. State one chemical difference between cotton (cellulose) and silk (protein), and predict how each behaves when burned.
Solution
Chemical difference: Cotton is cellulose (polysaccharide), composed of C, H, O only. Silk is protein, also containing N and S in addition to C, H, O.
When burned:
- Cotton: burns like paper with minimal residue
- Silk: smells like burning hair (due to N and S in protein) and curls into a hard bead