Kevlar

In-depth explanation of Kevlar

Kevlar is an aramid, a wholly aromatic polyamide made from para-phenylenediamine and terephthaloyl chloride. Its rigid, rod-like chains are highly aligned in the fibre by spinning from a liquid crystalline solution, and extensive hydrogen bonds link neighbouring chains. This alignment and bonding give the fibre a very high tensile strength and stiffness for its weight, roughly five times that of steel on a weight basis. Kevlar is used in body armour, helmets, cut-resistant gloves, tyres and ropes. It degrades under UV light and must be protected in long-term outdoor use.

Going deeper: Kevlar

Key ideas: An aromatic polyamide (aramid) from benzene-1,4-diamine and benzene-1,4-dicarbonyl chloride, condensation with loss of HCl. Rigid rod chains line up in sheets held by hydrogen bonds, giving tensile strength about five times that of steel by weight. Used for bulletproof vests, tyres, ropes and helmets.

Common mistakes and connections: Mistake: thinking it is strong because of thick fibers; it is chain alignment and hydrogen bonding plus rigid aromatic rings. It resists cutting less than impact. UV degrades it. Compare to nylon, whose flexible aliphatic chains make it stretchier. Links to nylon, liquid crystals and composites.

Visualization of Kevlar

Approximate tensile strength. Aligned, hydrogen-bonded aromatic chains give Kevlar several times the strength of steel, and far more on a weight basis. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Bulletproof vests use layers of woven Kevlar to absorb and spread the energy of a bullet.

Where Kevlar fits in Biochemistry, Environment & Industry

Kevlar is topic 59 of 127 in Biochemistry, Environment & Industry.

Related topics

• NylonIntermediate
• PolyesterIntermediate
• TeflonIntermediate
• BakeliteIntermediate
• PolystyreneIntermediate
• CopolymersAdvanced

Browse all 127 topics in Biochemistry, Environment & Industry