Self-Crimping Bicomponent Fibre Technology

Self-crimping bicomponent fibres exploit differential thermal shrinkage or differential crystallisation rates between two polymer components in side-by-side or eccentric core-sheath configuration to generate spontaneous 3D helical crimp on heat activation — producing bulky, elastic fibre without mechanical crimping or false-twist texturing. Side-by-side PET/PTT bicomponent (Invista Lycra T400, Toray Solo): PET component (standard melt viscosity 0.65 IV, shrinkage at 180°C 5–8%) + PTT polytrimethylene terephthalate component (0.92 IV, shrinkage at 180°C 20–30%) melt-spun from bicomponent spinneret (Hills type, PET/PTT 50:50 volume ratio) → POY wound at 3,000 m/min → draw-textured on FDY machine (175°C heater) → PTT component shrinks 20–30% versus PET 5–8% on heat → differential lateral stress → helical 3D crimp (1–3 mm pitch helix, crimp contraction 15–25%). Lycra T400 properties: elongation 25–35% (versus 400–600% elastane), elastic recovery 90–95% (versus 97–99% elastane), chlorine resistance grade 4–5 (versus grade 2–3 for PTMEG elastane), dyeable with disperse dyes simultaneously with PET component (versus acid dye for elastane requiring separate dyeing step), recyclable (both components PET/PTT — melt recycle compatible versus elastane non-recyclable). T400 application in stretch denim: 2–3% T400 in weft gives 20–25% stretch recovery versus 1.5–2.5% elastane — T400 denim more sustainable (recyclable, no DMAc solvent), handles at 180–200°C heat-setting without elastane degradation risk, and allows chlorine bleach washing acceptable for denim. PA6/PA66 bicomponent self-crimp (Asahi Kasei Roica SF bicomponent): PA6 (Tg 50°C) + PA66 (Tg 70°C) side-by-side → differential shrinkage in hot water and dry heat → helical crimp for stretch hosiery and seamless knit base layers. Side-by-side PET bicomponent with different IV: 0.62 IV / 0.92 IV PET bicomponent → differential crystallisation rate → self-crimp for fibrefill and wadding bulkiness without mechanical crimp.