## 4 Conclusions  
This study demonstrated the effectiveness of USM for processing P3 HB with minimal molecular degradation. By optimizing parameters such as wave amplitude and plunger velocity, USM achieved molecular weight retention with less than 3% degradation. Compared to conventional microinjection, USM produced highly uniform samples with enhanced mechanical properties and consistent performance, underscoring its advantages for processing thermally sensitive biopolymers. USM also proved effective in producing exfoliated P3 HB nanocomposites with both Cloisite C20 (treated) and Cloisite 116 (untreated) clays. The nanocomposites containing Cloisite C20 exhibited superior thermal stability and mechanical performance due to \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & \(E\) **(MPa)** & \(\sigma_{\text{max}}\) **(MPa)** & \(\varepsilon\) **(\%)** \\ \hline P3 HB 1  & 1560 \(\pm\) 76 & 31.7 \(\pm\) 1.2 & 5.0 \(\pm\) 0.2 \\ P3 HB 2  & 1390 \(\pm\) 45 & 25.9 \(\pm\) 4.1 & 6.0 \(\pm\) 0.3 \\ PHB3C20 1  & 1850 \(\pm\) 42 & 27.9 \(\pm\) 3.5 & 3.1 \(\pm\) 0.1 \\ PHB5C20 1  & 1990 \(\pm\) 51 & 29.2 \(\pm\) 2.3 & 3.2 \(\pm\) 0.2 \\ PHB8C20 1  & 2140 \(\pm\) 55 & 29.2 \(\pm\) 3.2 & 2.7 \(\pm\) 0.1 \\ PHB3C20 1  & 1480 \(\pm\) 62 & 26.2 \(\pm\) 2.6 & 2.6 \(\pm\) 0.2 \\ PHB5C20 1  & 1270 \(\pm\) 42 & 24.9 \(\pm\) 2.8 & 2.4 \(\pm\) 0.3 \\ PHB8C20 1  & 1570 \(\pm\) 54 & 25.2 \(\pm\) 3.0 & 1.8 \(\pm\) 0.2 \\ PHB3C116 1  & 1840 \(\pm\) 52 & 27.5 \(\pm\) 3.4 & 2.5 \(\pm\) 0.2 \\ PHB5C116  & 2010 \(\pm\) 84 & 26.2 \(\pm\) 4.1 & 2.3 \(\pm\) 0.3 \\ PHB8C116 1  & 2190 \(\pm\) 68 & 20.6 \(\pm\) 2.6 & 1.3 \(\pm\) 0.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Young modulus (_E_), maximum strength (\(\sigma_{\text{max}}\)), and strain at break (\(\epsilon\)) for processed specimens of P3 HB and correspond nanocomposites with C20 and C166 clays. improved dispersion and stronger interfacial bonding with the P3 HB matrix. In contrast, Cloisite C116 nanocomposites posed significant challenges during processing, with notable molecular weight reduction and accelerated thermal degradation attributed to the catalytic effects of untreated clay surfaces. USM successfully mitigated these issues by minimizing thermal exposure, whereas conventional microinjection failed to produce viable specimens with Cloisite C116. The mechanical analysis revealed that the incorporation of nanoclays enhanced stiffness, reflected in an increase in Young's modulus while reducing ductility, as seen in the decrease in strain at break. This trade-off is consistent with the behavior of polymer nanocomposites. Furthermore, the addition of nanoclays influenced the crystallization behavior of P3 HB, promoting the formation of larger crystalline domains but without altering thermodynamic equilibrium conditions. Overall, this study highlights USM as a viable and superior alternative for producing P3 HB and its nanocomposites, particularly in scenarios where conventional methods are limited by thermal degradation and poor material flow. These findings provide valuable insights into optimizing P3 HB processing and tailoring its properties for advanced applications in bioplastics and nanocomposites. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app142411959/s1](https://www.mdpi.com/article/10.3390/app142411959/s1)]([https://www.mdpi.com/article/10.3390/app142411959/s1](https://www.mdpi.com/article/10.3390/app142411959/s1)). Conceptualization, G.P., E.F., A.J., and J.P.; methodology, G.P., E.F., and A.J. ; formal analysis, G.P. ; investigation, G.P., A.J., E.F., L.J.A.V., and J.P.; writing--original draft preparation, G.P., A.J., and J.P.; writing--review and editing, G.P., A.J., L.J.A.V., and J.P.; supervision, E.F., L.J.A.V. and J.P. All authors have read and agreed to the published version of the manuscript. This research was funded by the Spanish Ministry of Economy and Competitiveness, grant number PID2022-140302 OB-I00; and the Generalitat de Catalunya, grant number 2021 SGR01042.