Tensile and Crystallization Behavior of Melt‐Spun Fibers Derived From Poly(Butylene Terephthalate‐Co‐2,6‐Naphthalate) Copolyester

ABSTRACT In this study, a series of poly(butylene terephthalate‐co‐2,6‐naphthalate) (PBTN) copolymers was synthesized via a one‐step polycondensation process. These PBTN copolymers demonstrate excellent thermal stability and semi‐crystalline behavior, with the enthalpy of melting values exceeding 17 J g −1 . Crystallization kinetics analysis revealed that the copolymers exhibit significantly higher crystallization rates than neat poly(butylene terephthalate) (PBT) and poly(butylene naphthalate) (PBN), making them well‐suited for fiber production. The copolymers were melt‐spun, followed by a post‐drawing process at a ratio of 2.0, to enhance fiber strength. By adjusting the 2,6‐naphthalene dicarboxylate (NDC) content, the mechanical properties and crystallinity of the PBTN fibers were fine‐tuned. Tensile testing revealed that the copolymer fiber containing 50 mol% NDC, post‐drawn at a ratio of 2.0, exhibits superior toughness, with maximum tenacity and elongation values of 3.13 g den −1 and 69.3%, respectively.