## 3 Results and Discussion
### Influence of Loaded Nanoclasys on Mechanical Properties  
P3 HB specimens were characterized by significant stiffness, high modulus, and limited strain at break. The mechanical properties of P3 HB were also influenced by aging, as increased crystallinity over time results in higher modulus but reduced strain at break. Figure 12a illustrates these aging effects, showing stress-strain curves for storage periods of 1 day, 1 month, and 1 year. To ensure consistency in comparison, all further mechanical measurements were conducted on specimens stored for only one day.  
Comparisons between USM and microinjected P3 HB specimens revealed distinct advantages of USM processing. As shown in Figure 12b, USM-processed specimens  
Figure 11: (**a**) DSC heating curves of the melt crystallized P3 HB/C20 nanocomposites at temperatures of 135 \({}^{\circ}\)C, 132 \({}^{\circ}\)C, 130 \({}^{\circ}\)C, 128 \({}^{\circ}\)C, and 125 \({}^{\circ}\)C from top to bottom; (**b**) Hoffman–Weeks plot for the P3 HB and P3 HB/C20 nanocomposite containing 5 wt% of clay.  
Figure 12: (**a**) Stress–strain curves for neat P3 HB specimens processed by USM with the nodal point configuration. Samples differ in the storage time: 1 day (blue), 1 month (red), 1 year (black); (**b**) Stress–strain curves for neat P3 HB (blue), PHBSC20 (red), and PHBSC166 (black) specimens processed by USM.  
exhibited higher tensile strength (31.7 MPa vs. 25.9 MPa) and modulus (1560 MPa vs. 1390 MPa) compared to their microinjected counterparts, despite a slight reduction in strain at break. These improvements highlight the benefits of the USM technique, having shorter residence times and reduced thermal degradation, which preserves the structure and mechanical performance of polymers.  
The incorporation of Cloisite C20 nanoclays into P3 HB resulted in a consistent increase in modulus with rising clay content. As shown in Table 2, the modulus of USM-processed P3 HB/C20 nanocomposites increased from 1850 MPa for 3 wt% clay to 2140 MPa for 8 wt% clay. However, this increase in modulus was accompanied by a reduction in the strain at break, with values decreasing from 5% from neat P3 HB to 3.1% and 2.7% for 3 wt% and 8 wt% clay contents, respectively.  
Tensile strength showed a more complex trend, increasing slightly with clay content (from 27.9 MPa to 29.2 MPa for 3 wt% to 8 wt% clay) but remaining slightly lower than that of the neat polymer. These results highlighted a trade-off between improved modulus and reduced ductility, a common characteristic of nanocomposite materials. The uniform dispersion and exfoliation of Cloisite C20, as observed in TEM and SEM analysis, likely contributed to the enhancement in modulus and strength.  
Similar trends were observed for nanocomposites incorporating Cloisite C116, where the modulus increased steadily from 1840 MPa for 3 wt% clay to 2190 MPa for 8 wt%. The stiffer nature of the untreated C116 clay contributed to these improvements. However, both tensile strength and strain at break exhibited significant reductions as the clay content increased, with tensile strength dropping to values below 25 MPa at higher clay concentrations. This behavior can be attributed to the molecular degradation associated with the catalytic activity of unmodified C116 clay, as evidenced by GPC and XRD analysis. Furthermore, the lack of surface modification in C116 likely limits its interfacial bonding with the P3 HB matrix, resulting in weaker load transfer and lower mechanical performance compared to Cloisite C20.