## 3 Results and Discussion
### Dispersion of Functionalized Silica Micro- and Nanoparticles by Ultrasound Micro-Moding Technology  
PE99 samples could be processed under relatively mild conditions, as previously established [15]. Thus, a minimum irradiation time of 1.2 s, low amplitude of 24 \(\upmu\)m, and a moderate molding force of 300 N were sufficient to guarantee a 100% molding efficiency. Experimental conditions could be maintained for processing mixtures with functionalized micro- and nanospheres up to the maximum test load of 6 wt. %. Molecular weights of raw PE99 and specimens processed under the above optimized conditions are summarized in Table 1, whereas Figure 6 compares the GPC traces of PE99, PE99-N 3, and PE99-M 6 specimens. Figure 5: TGA (**a**) and DTGA (**b**) curves of silica nanospheres, functionalized silica nanospheres, and micro-molded PE99, PE99-N 3, and PE99-M 6 specimens. No statistically significant differences were found between samples before and after processing or upon addition of functionalized nanospheres. Only a not highly significant decrease was detected for samples loaded with the maximum percentage (6 wt. %) of microspheres. The new technology appears fully adequate to obtain micropieces with negligible degradation of composites constituted by PE99 and functionalized silica micro/nanoparticles. Figure 7a,b show optical and SEM images of a representative silica loaded specimen for which a regular texture is detected in the longitudinal section micrographs. All specimens were highly homogeneous, without the presence of cavities that could affect the final properties of the material. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & _Mn_ **(g/mol)** & _Mw_ **(g/mol)** & _Mw/Mn_ \\ \hline PE99 (raw) & 13,300 & 35,900 & 2.7 \\ PE99 & 14,700 & 37,200 & 2.5 \\ PE99-M 3 & 14,800 & 36,800 & 2.5 \\ PE99-M 6 & 12,600 & 33,800 & 2.7 \\ PE99-N 3 & 15,800 & 39,200 & 2.5 \\ PE99-N 6 & 14,200 & 37,900 & 2.7 \\ \hline \end{tabular}  
* Micro-molding conditions: Time (s), amplitude (\(\mu\)m) and force (N): 1.2, 10 and 300.  
\end{table} 
Table 1: Molecular weights of processed PE 99 and their mixtures with functionalized micro- and nanoparticles \({}^{\mathrm{a}}\). Figure 6: GPC molecular weight distribution curves determined for micro-molded PE99, PE-N 3, and PE99-M 6 specimens. FTIR spectra were also useful to verify the uniform incorporation of silica particles into micro-molded specimens and to discard concentration in the sprue. Thus, the typical Si-O stretching band at 1075 cm\({}^{-1}\) was observed in every part of all loaded specimens. Hence, the spectra of specimen zones close to (proximal part) and distant from (distal part) the feeding channel showed a similar ratio between the intensity of the band associated with the C=O stretching band of the polyester and the band associated with the silica particles (see Figure 8 for representative samples containing micro- and nanoparticles). Analysis of particle dispersion in the processed composites was also carried out by transmission electron microscopy observation of ultrathin sections of micro-molded specimens. Flawless ultrasonics could be obtained, as can be seen in the images for representative samples in Figure 9. These micrographs show the distribution of micro- and nanoparticles in the specimen, which is not completely homogeneous since density appears to be locally variable when observed at this scale. Figure 8: FTIR spectra of the characteristic C=O and Si–O stretching bands of micro-molded PE-N 3 (**a**) and PE-M 3 (**b**) specimens. Blue and red lines correspond to the proximal and distal parts of the specimens, respectively. Figure 7: Image of a processed PE99 specimen (**a**); SEM micrograph of details of a micro-molded PE99-M 3 specimen (**b**). Microparticles can be observed in the inset. Thermogravimetric analysis also gave information about the percentage of silica particles incorporated into the polymer matrix and their effect on thermal stability.