Double Spherulite Formation via Two-Step Crystallization in PTT/PET Blends.

Area of Science:

• Polymer Science
• Materials Science
• Crystallization Kinetics

Background:

• Miscible crystalline/crystalline polymer blends exhibit complex crystallization behaviors.
• Understanding morphology evolution is crucial for tailoring material properties.

Purpose of the Study:

• To investigate the crystallization kinetics and morphology evolution of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) (PET) blends.
• To elucidate the two-step crystallization mechanism and the formation of double spherulites.

Main Methods:

• Isothermal melt crystallization at 215 °C.
• Integrated light-scattering intensity measurements.
• Atomic force microscopy (AFM) for morphology analysis.

Main Results:

• A two-step crystallization process was observed in 70/30 PTT/PET blends.
• The first step involved compact poly(ethylene terephthalate) (PET) spherulite growth, followed by dendritic poly(trimethylene terephthalate) (PTT) spherulite growth.
• Atomic force microscopy revealed interfiled PTT fibrils within PET spherulites, forming a double-spherulite structure with PET inner and PTT outer regions.

Conclusions:

• The observed double-spherulite structure results from the sequential crystallization of PET and PTT.
• PTT exclusion from the PET crystal growth front drives the interfiling and subsequent outward growth of PTT fibrils.
• This study provides insights into the complex crystallization mechanisms in polymer blends.