Elastane (Spandex / Lycra) Fibre

Elastane (generic name: elastane EU, spandex USA) is a segmented polyurethane-polyurea copolymer fibre providing exceptional elastic recovery — elongating 400–800% at break with >97% elastic recovery after repeated stretch cycles — produced by dry spinning of polyurethane solutions or melt spinning of thermoplastic polyurethane (TPU). Lycra (Invista brand, originally DuPont 1958, acquired Invista 2003; also produced as Spandex, Roica by Asahi Kasei, CREORA by Hyosung, Dorlastin by Covestro) production 1.2 million tonnes (2023) — China 70% of production (Hyosung Huvis, Yantai Tayho, Huafon Group). Segmented block copolymer structure: soft segments (polyether — PTMEG polytetramethylene ether glycol Mw 1,000–3,000 — or polyester diol) alternating with hard segments (MDI 4,4'-diphenylmethane diisocyanate + diamine chain extender — ethylene diamine EDA forms urea linkages –NH–CO–NH– between hard segments). Soft segment PTMEG: Tg −60°C to −70°C (highly mobile, entropic elastic recovery similar to rubber), crystallinity 0–5% — provides the rubbery elasticity; hard segment MDI-urea: Tg +50–80°C (rigid, polar hydrogen bonding between –NH and C=O groups) — aggregates into hard segment domains providing physical crosslinks that set recovery force and dimensional stability. Fibre properties: tenacity 0.6–0.9 cN/dtex (low — elastane is used as core yarn, not for strength), elongation at break 400–800%, elastic recovery from 100% extension >97% (after 5 cycles), modulus 0.005–0.012 cN/dtex (extremely low — very little force required for extension), heat setting at 190–200°C fixes fabric geometry, dyeable with acid dyes and disperse dyes. End-use: swimwear (18–22% elastane), intimate apparel bra and underwear (8–15%), hosiery (2–5%), sportswear compression (10–20%), denim stretch (1–3% elastane, Lycra T400 PET/PTT bicomponent combination), circular knit jerseys (3–8%).