Tuning the Structure and Properties of Poly(ethylene terephthalate)/Poly(butylene terephthalate) Blend Monofilaments: Mechanism of Transesterification and Gradient Structure Development

Abstract

To address the limited toughness of poly(ethylene terephthalate) (PET) monofilaments arising from the inherent molecular chain rigidity, this study prepared PET/poly(butylene terephthalate) (PBT) blend monofilaments via the melt-blend spinning method to enhance their toughness. The influence of PBT content on the structural evolution and properties of the blend system was systematically investigated. These results indicate that the PBT content significantly influences the extent of transesterification and compatibility, thereby dictating the mechanical behavior of the monofilaments. At a low PBT content of 2 wt%, transesterification was negligible. The monofilaments exhibited a uniform radial gradient orientation without a distinct skin-core structure, demonstrating optimal overall mechanical performance with markedly improved strength. Specifically, the tensile, loop, and knot strengths were 611, 421, and 443 MPa, respectively. When the PBT content exceeded 5 wt%, the flexible chain segments of PBT enhanced the molecular chain mobility in the blend chips, leading to an increase in crystallite size. However, intensified transesterification concurrently reduces the crystallizability and degrades the mechanical properties. At PBT contents above 15 wt%, SEM analysis revealed phase separation and pronounced heterogeneity in the radial gradient structure of the blend monofilaments, resulting in a significant deterioration of the mechanical properties. This study elucidates the pivotal role of blending ratio in governing the “composition-structure-property” relationship of PET/PBT-blended monofilaments, revealing the underlying mechanism of transesterification and gradient structure development. These findings provide a theoretical foundation for the design of high-performance PET monofilaments.