## 3 Results and Discussion
### Isothermal Crystallization and Kinetic Analysis  
#### 3.3.1 Crystallization of Neat and Nucleated P3 HBHHx at Different Isothermal Temperatures  
The non-isothermal DSC results identified boron nitride (BN) as the most effective nucleating agent for P3 HBHHx, increasing the crystallization temperature (\(T_{\rm c}\)) from 36.4 \({}^{\circ}\)C in neat P3 HBHHx to 84.1 \({}^{\circ}\)C. PHB and talc (2 wt%) also showed significant effects, increasing the \(T_{\rm c}\) to 81.9 \({}^{\circ}\)C and 72.6 \({}^{\circ}\)C, respectively. To further investigate the crystallization behavior and kinetics, isothermal crystallization experiments were conducted at various temperatures for these samples. Figure 11 shows the DSC exothermic peaks corresponding to the isothermal crystallization of the neat and nucleated P3 HBHHx samples. When the isothermal temperature closely approaches the crystallization temperature identified in the non-isothermal analysis, the crystallization peaks are sharp and well-defined, indicating rapid nucleation and crystal growth. In contrast, at higher isothermal temperatures, the peaks become broader and appear after longer induction times, reflecting a reduced thermodynamic driving force for crystallization and slower kinetics. It is important to note that for a reliable kinetic analysis, the selected isothermal temperature must enable full crystallization during the isothermal hold. For example, although the crystallization of neat P3 HBHHx (Figure 11a) at 50 \({}^{\circ}\)C occurs rapidly with a sharp and defined peak, the crystallization enthalpy determined was only 41.5 J/g (Table 6), significantly lower than the 60.3 J/g measured at higher temperatures (80 \({}^{\circ}\)C and above). This suggests that a substantial portion of the material had already crystallized during the rapid cooling step prior to reaching the isothermal temperature. Consequently, this condition does not accurately reflect isothermal crystallization and is unsuitable for kinetic modeling. Figure 10: Mechanical properties of PHH_05 BN injected at different mold temperatures. (**a**) Young’s modulus, (**b**) tensile strength, and (**c**) elongation at break. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{
\begin{tabular}{c} **Isothermal** \\ **Temperature** (\({}^{\circ}\)**C) \\ \end{tabular} } & \multicolumn{2}{c}{**Enthalpy of**} & \multicolumn{2}{c}{**Half-Time of**} & \multicolumn{1}{c}{**Crystallization**} \\  & **Crystalliza-** & **Crystalliza-** & **Crystalliza-** & **Rate** \\  & & & **tion** \(\tau_{\textbf{(1/2)}}\) **(s)** & \(k\times\textbf{10}^{3}\) **(s\({}^{-1}\))** \\ \hline \multirow{4}{*}{P3 HBHHx} & 50 & 41.5 & 77 & 13.06 \\  & 70 & 55.1 & 159 & 6.27 \\ \cline{1-1}  & 80 & 60.3 & 340 & 2.94 \\ \cline{1-1}  & 85 & 60.1 & 726 & 1.38 \\ \cline{1-1}  & 95 & 60.8 & 1404 & 0.71 \\ \hline \multirow{4}{*}{PHH\_05 BN} & 95 & 48.1 & 68 & 14.67 \\  & 100 & 64.3 & 99 & 10.05 \\ \cline{1-1}  & 105 & 66.5 & 173 & 5.77 \\ \cline{1-1}  & 110 & 66.7 & 306 & 3.27 \\ \hline \multirow{4}{*}{PHH\_05 PHB} & 85 & 46.9 & 104 & 9.66 \\ \cline{1-1}  & 90 & 59.4 & 165 & 6.06 \\ \cline{1-1}  & 95 & 60.2 & 193 & 5.18 \\ \cline{1-1}  & 100 & 60.5 & 242 & 4.13 \\ \hline \multirow{4}{*}{PHH\_2 Talc} & 85 & 44.5 & 84 & 11.84 \\ \cline{1-1}  & 90 & 55.6 & 106 & 9.47 \\ \cline{1-1} \cline{2-5}  & 95 & 58.0 & 133 & 7.53 \\ \cline{1-1}  & 100 & 58.4 & 244 & 4.09 \\ \cline{1-1}  & 105 & 60.3 & 434 & 2.31 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summarized data of the isothermal crystallization process for P3 HBHfx and various nucleating agents at different temperatures obtained from DSC. Figure 11: DSC exothermic peaks corresponding to the different isothermal crystallization temperatures for (**a**) P3 HBHfx, (**b**) PHH_05 BN, (**c**) PHH_05 PHB, and (**d**) PHH_2 Talc. The same criterion applies to the nucleated samples. For example, PHH_05 BN required isothermal temperatures of 100 \({}^{\circ}\)C or higher to avoid partial crystallization during cooling.