Lecture Notes: The Invention of Kevlar

Introduction

• Richard Davis tested bulletproof vests by shooting himself 192 times to demonstrate their effectiveness.
• The demonstration highlighted the vest's ability to stop bullets despite its lightweight design.

Key Figure: Stephanie Kwolek

• Kwolek was a material chemist working for DuPont in the 1960s.
• Her task was to create a stronger synthetic fiber for durable, lightweight tires.

Synthetic Fibers and Polymers

• Nylon: First synthetic fiber, a polymer with repeating monomers.
• Polymers: Long chains of molecules that can have varying properties based on their monomers and bonding patterns.

Discovery of Kevlar

• Kwolek's process involved trial and error with different monomers.
• Kevlar was created from 1,4-phenylene-diamine and terephthaloyl chloride, forming parallel chains at the molecular level.
• Characteristics of Kevlar:
  • Order and Strength: Chains align in rows, providing crystalline strength.
  • Liquid Crystal Polymer: Changes state under pressure, allowing flexibility and absorption of energy.

Comparison with Metals

• Metals: Strong atomic bonds provide resilience against penetration (e.g., steel vs. wood).
• Kevlar's Bonds: Weaker than metals but have numerous hydrogen bonds that require substantial energy to overcome.

Mechanism of Impact Absorption

• Kevlar's woven threads absorb impact energy through the movement of polymer chains.
• If a bullet penetrates, it does so at a reduced speed and force.

Limitations of Kevlar

• Kevlar is not completely immune to damage.
• Strong forces can be transmitted through the fabric.
• Fibers lose strength under UV light exposure.
• New liquid crystal fibers perform better against acid.

Applications of Kevlar

• Kevlar is widely used in various industries due to its properties:
  • Helmets
  • Kayaks
  • Spacecraft
  • Automobiles
  • Speakers (efficient in air movement)
  • Tires

Conclusion

• Kwolek's invention of Kevlar is one of the most versatile and widely used materials in modern applications.