## 3 Results and Discussion
### Spherulitic Morphology and Crystal Growth of P3 HBHHx Samples  
#### 3.4.1 Spherulitic Morphology  
The spherulitic morphologies of neat P3 HBHHx and the nucleated samples were examined at various isothermal temperatures using polarized optical microscopy (POM). Representative micrographs are shown in Figure 15, highlighting the significant differences in morphology and nucleation density among the samples.  
For neat P3 HBHHx (Figure 15a), no spherulites were observed at temperatures above 65 \({}^{\circ}\)C, even after prolonged observation (e.g., approximately 30 min at 70 \({}^{\circ}\)C). The absence of crystalline structures demonstrates the difficulty in forming homogeneous primary nuclei, which require significant supercooling to initiate. At 65 \({}^{\circ}\)C, large spherulites with extensive radial growth appeared, although the density of the primary nuclei remained low.  
Figure 14: (**a**) Comparison between the crystallization rates (**a**) and crystallization half-times (**b**) obtained directly from DSC curves (solid lines) and those deduced from the Avrami analyses (dashed lines). Spherulitic morphologies of the P3 HBHHx samples.  
These spherulites exhibited coarse textures with irregular Maltese-cross patterns, indicative of non-uniform lamellar packing, likely caused by variations in lamellar orientation and thickness [43].  
At 60 \({}^{\circ}\)C, the spherulites began to display regular bands, indicating a transition in the crystallization mechanism. This banded structure is associated with the periodic twisting of lamellae during radial growth [44], and the resulting birefringence contrast between edge-on and flat-on lamellae leads to the observed alternating bright and dark rings. Surface stresses have been proposed to drive this twisting behavior [45; 46; 47]. At 50 \({}^{\circ}\)C, the morphology remained banded, but the spherulite size decreased, and the nucleation density increased markedly, resulting in a dense arrangement of small, banded spherulites.  
For the nucleated samples (Figure 15b-d), spherulites were observed even at elevated temperatures, such as 100 \({}^{\circ}\)C, indicating that heterogeneous crystallization was effectively promoted by the incorporated nucleating agents. At this temperature, the morphology was characterized by coarse textures and irregular Maltese-cross patterns, similar to those of neat P3 HBHJK at 65 \({}^{\circ}\)C. As the isothermal temperature decreased, the nucleation density increased, leading to the formation of finer and more densely packed spherulites with banded structures. This morphology results from the combined effects of heterogeneous nucleation induced by the additives and homogeneous nucleation inherent to the neat polymer at high degrees of supercooling.  
Interestingly, the nucleation density in the nucleated samples was lower than that in the neat polymer, resulting in the formation of larger spherulites. Polarized optical  
Figure 15: Spherulitic morphology of (**a**) P3 HBHrk, (**b**) PHH_05 BN, (**c**) PHH_05 PHB, and (**d**) PHH_2 Talc at different crystallization temperatures. Micrographs taken at 100 \({}^{\circ}\)C correspond to periods between 2 and 4 min, except for the neat polymer, which was taken after 30 min.  
micrographs revealed the coexistence of two spherulitic populations: larger spherulites attributed to rapid heterogeneous nucleation and smaller spherulites associated with slower homogeneous nucleation. In particular, the PHH_05 BN samples continued to exhibit irregular Maltese-cross patterns even at lower temperatures, suggesting a distinct crystallization mechanism that may be influenced by specific interactions between boron nitride and the P3 HBHHx matrix.