## 3 Results and Discussion
### Optimization of USM Processing Parameters
#### 3.2.3 Chemical Structure: NMR and FTIR Results  
The comparison of \({}^{13}\)C-NMR and \({}^{1}\)H-NMR spectra for P3 HB before and after processing with both conventional microinjection and USM technology under optimized conditions revealed no significant differences in chemical structure. This indicates there was no appreciable degradation across both processing techniques. The observed peaks are consistent with those reported in various literature sources [27; 28; 29; 30].  
In the \({}^{1}\)H-NMR spectra (Figure 4a), three distinct types of peaks were noted: a doublet at \(\delta\) 1.26-1.28 ppm, which corresponded to the protons in the methyl side chain; a multiplet at \(\delta\) 5.22-5.30 ppm, associated with the protons on the CH group near the oxygen atom; and a complex peak at \(\delta\) 2.44-2.63 ppm, which represented a doublet of a quadruplet from the methylene group (-CH\({}_{2}\)-). The presence of the quadruplet confirmed the proximity of the methyl side chain to the methylene group, reflecting the compact molecular structure of P3 HB. These peaks showed no shifts or intensity changes across different processing methods, highlighting the absence of chemical degradation.  
Figure 3: SEM micrographs showing different low magnification images of microinjected (**a**) and USM P3 HB specimens (**b**). Outer (top) and cross-section (bottom) images are provided; (**c**) SEM micrograph showing a cross-section of a USM micromolded P3 HB specimen where spherulitic aggregates with radial lamellae can be envisaged (white dashed ellipsoid).  
In the \({}^{13}\)C-NMR spectra (Figure 4b), four major peaks were identified: at \(\delta\) 169 ppm for the carbonyl carbon, \(\delta\) 67 ppm for carbon linked to oxygen, \(\delta\) 41 ppm for the methylene group -CH\({}_{2}\)-, and \(\delta\) 20 ppm for the carbon in the methyl side chain. Like the \({}^{1}\)H-NMR results, the \({}^{13}\)C-NMR spectra exhibited no significant variations in peak positions or intensities, reinforcing the structural stability of P3 HB. Although GPC analysis indicated a molecular weight reduction of approximately 17,000 g/mol in conventional microinjection-processed samples, no corresponding minor peaks for terminal groups were detected near \(\delta\) 170 ppm in the \({}^{13}\)C-NMR spectra. This suggests that although molecular weight reduction occurred, its ratio was too low to be detected.  
The FTIR spectra of the P3 HB raw material (extruded pellets) were analyzed and compared to those obtained from samples produced through conventional microinjec  
Figure 4: (**a**) \({}^{1}\)H NMR and (**b**) \({}^{13}\)C NMR spectra and magnified peaks for raw P3 HB (blue), conventional micromolded (red), and USM samples (black) processed under optimized conditions.  
tion and ultrasonic micromodling (USM) under both optimal and non-optimal conditions. Figure 5 illustrates the characteristic P3 HB bands present in all samples, including CH\({}_{2}\) at 2974 cm\({}^{-1}\) and 2933 cm\({}^{-1}\), C=O at 1719 cm\({}^{-1}\), and -C-O at 1277 cm\({}^{-1}\) and 1054 cm\({}^{-1}\). These spectra were largely consistent across different samples, except for those produced under non-optimal USM parameters. These samples exhibited signs of degradation, as evidenced by the splitting of the C=O band and variations in the intensity of bands around 1200 cm\({}^{-1}\) (highlighted by a black ellipsoid in Figure 5). These changes suggest polymer chain scission and possible oxidation under non-optimal ultrasonic parameters, emphasizing the importance of precise control over USM settings to prevent thermal and mechanical degradation.