Competing crystallization behaviors and microstructural evolution in poly(trimethylene terephthalate)/poly(butylene terephthalate) blends

Abstract This study systematically investigates the competitive crystallization behavior and microstructural and morphological transition in poly(trimethylene terephthalate)/poly(butylene terephthalate) (PTT/PBT) blends across the full composition range. Through a combined approach of DSC, XRD and polarized light optical microscopy (PLOM), we demonstrate that the blends exhibit distinct non‐equilibrium pseudo‐eutectic characteristics, with minimum crystallization temperature ( T c ) and melting temperature ( T m ) observed near intermediate compositions. The crystallization activation energy from isothermal crystallization kinetics (Avrami–Arrhenius method, resulting from the diffusion‐controlled growth barrier) and non‐isothermal crystallization kinetics (Kissinger, the total energy barrier dominated by nucleation) consistently identify the lowest activation energy value near intermediate compositions—attributed to molecular chain interlocking and constrained crystallization dynamics, thereby corroborating synergistic crystallization suppression in the pseudo‐eutectic regime. The Avrami exponent exhibits a characteristic arc‐shaped variation (first increasing then decreasing), indicating a transition in nucleation and growth mechanisms. XRD analyses further confirm lattice expansion in the PTT‐rich phase and crystallite refinement in pseudo‐eutectic regions, while PLOM captures the progressive disruption of spherulitic morphology with increasing PBT content. This work establishes a coherent correlation between composition, crystallization behavior and multi‐scale structure, providing critical insights for the tailored design of high‐performance polyester blends. © 2026 Society of Chemical Industry.