Polyamide (Nylon) Fibre

Polyamide fibres (nylon) are produced by polycondensation or ring-opening polymerisation of diamine-diacid salts (nylon 66: hexamethylene diamine + adipic acid → PA66 polymer) or lactam ring-opening (nylon 6: ε-caprolactam + water catalyst → PA6 polymer) to form semi-crystalline polyamide chains characterised by recurring amide linkages –CO–NH– providing hydrogen bonding capability, dyeability with acid dyes, and superior abrasion resistance. Global production 6.0 million tonnes (2023): PA6 4.0 million tonnes (caprolactam-based, dominant in Europe and Asia — BASF, Aquafil, Radici, Lanxess); PA66 2.0 million tonnes (salt-based, USA dominant — Invista Lycra Type 6.6, Ascend Performance Materials, Solvay). Key PA6 properties: density 1.14 g/cm³ (lighter than PET), tenacity 4.0–7.0 cN/tex, elongation 20–35%, moisture regain 4.0–4.5% (10× higher than PET — contributes superior comfort and static resistance), melting point 220°C (Tm, PA6) versus 258°C (PA66), Tg 50°C (PA6) versus 70°C (PA66). PA66 advantages over PA6: higher Tg (70°C versus 50°C) and melting point (258°C versus 220°C) give better dimensional stability at elevated temperatures (automotive, industrial applications), superior fatigue resistance (tyre cord, conveyor belts), slightly higher tenacity (7.0–8.5 cN/tex PA66 versus 6.5–8.0 cN/tex PA6 for industrial yarn). PA6 advantages: lower polymerisation temperature, easier reprocessing (lower MW required for textile), better dyeability (more amide groups accessible, more open fibre structure), lower caprolactam monomer cost $1,800–2,400/tonne versus adipic acid/HMD salt $2,500–3,500/tonne for PA66. End-uses by type: PA6 hosiery (92% of global hosiery uses PA6 or PA66), intimate apparel, swimwear, sportswear, carpet face fibre (BCF trilobal, solution-dyed); PA66 tyre cord (1,890 dtex, 2-ply twisted, 360 TPI), airbag fabric, technical ropes.