PBT (Polybutylene Terephthalate) Fibre
topic
PBT (polybutylene terephthalate): polyester with 1,4-butanediol instead of EG. Gauche–gauche conformation of –(CH₂)₄– spacer provides elasticity (70% recovery at 30% extension). Tg ~45°C, Tm 223–227°C. Very fast crystallisation rate (unlike slow-crystallising PET). Bicomponent PET/PBT side-by-side fibres develop spontaneous 3D helical crimp from differential shrinkage, producing elastic fabrics without elastane. Low temperature dye uptake at 100°C.
Role
PBT's faster crystallisation and elastic recovery differentiate it from PET and PTT. PET/PBT bicomponent elastic fibre technology is an important alternative to elastane (spandex) for eco-friendly stretch fabrics without urethane chemistry.