Kevlar® (DuPont™)

Kevlar^® (DuPont™)

Kevlar^® is a trademark for para-aramid synthetic fiber developed in 1965 by chemist Stephanie Kwolek at DuPont™. It was introduced to the market in 1971 and has since found wide use in industry, protection, and sports due to its exceptional strength, low weight, and thermal resistance.

Properties of Kevlar^®

• Tensile strength: 20–21 cN/dtex
• Modulus of elasticity: 3.6–4.1 GPa
• Relative density: 1.44 g/cm³
• Elongation: 2.8–4%
• Temperature resistance:
  • 10% strength decrease at 160°C (after 500 hours)
  • 50% strength decrease at 260°C (after 70 hours)
  • Sublimation at 450°C
• Stability at cryogenic temperatures (–196°C)
• High impact energy absorption capacity

Disadvantages

• Sensitivity to UV radiation and moisture
• Unsuitability for compressive loads
• Difficult processing (special scissors required)
• Difficult to dye

Manufacturing and Chemical Composition

Kevlar^® is synthesized from para-phenylenediamine and terephthaloyl chloride. N-methylpyrrolidone is used as a solvent and calcium chloride as an ionic component. The resulting solution is spun through nozzles and drawn into a coagulation bath. The fibers are dried and stretched at temperatures of 300–400°C.

Molecular formula: [-CO-C₆H₄-CO-NH-C₆H₄-NH-]ₙ

According to the definition by the Federal Trade Commission (USA), aramid fibers must contain at least 85% of the amide bonds attached to aromatic rings.

Delivery Forms

• Filament: 22–167 tex (yarns, rovings)
• Staple fiber: 1.7 dtex (38–50 mm length)
• Chopped material: 1–100 mm length

Uses of Kevlar^®

• Ballistic protection (vests, helmets)
• Aerospace – aircraft and shuttle construction
• Brakes, landing gear, reinforcements
• Telecommunication cables
• Sports equipment and footwear
• Automotive industry (belts)