Mechanism of the Formation of Concentric Ring-like Patterns on PHBV Spherulites

Polymers of the 3-hydroxybutyrate-co-3-hydroxyvalerate type are ideal systems for the study of spherulite morphology. The growth of spherulites was studied using polarizing microscopy with heat-stage and scanning electron microscopy (SEM). Some concentric ring features on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV spherulite were observed. The SEM photos proved that the concentric rings occur on the surface of spherulite. And it's a “Z”-shape feature, the outer ring is higher than the inner. The factors that influence the phenomenon include the temperature, the thickness of film, and the radius of the spherulite, etc. The possible mechanism of this phenomenon is given. It is postulated that the concentric rings are formed by the change on physical parameters when crystallizing.