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

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.