## 3 Results and Discussion
### Ultrasound Micromolding of PLA/PEG Blends
Note that a relatively homogeneous specimen was obtained for a theoretical PEG content of 15 wt-%, which contrasts with the high heterogeneity detected for the sample containing 30 wt-%. \({}^{1}\)H RMN spectra gave more quantitative results about the specimen uniformity as shown in Figure 7 and Table 2 for representative specimens obtained from mixtures containing 15 wt-%, 30 wt-% and 50 wt-% of PEG. Again, spectra were taken from the P and D parts of each processed sample. Spectra were characterized by PLA peaks at 1.56 ppm (-CH\({}_{3}\), d) and 5.15 ppm (-CH-, q) and the PEG peak at 3.64 ppm (-CH\({}_{2}\)-, s). Table 2 shows the value of integrated area for a representative peak of each polymer and the deduced PEG content according to Equation (5):  
\[\text{PEG (wt-\%)}=100\times(A_{3.64}/4)\times 60/[(A_{3.64}/4)\times 60+(A_{1. 56}/3)\times 72\] \begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **1.56 ppm (-CH\({}_{3}\))** & **3.64 ppm (-CH\({}_{2}\)-)** & **PEG (wt-\%)** \\ \hline PLA: PEG 85\% P & 4.49 & 0.52 & 8.0 \\ PLA: PEG 85\% D & 5.03 & 0.45 & 7.2 \\ PLA: PEG 70\% P & 3.65 & 0.82 & 14.4 \\ PLA: PEG 70\% D & 4.92 & 0.77 & 10.5 \\ PLA: PEG 50\% P & 1.06 & 1.42 & 50.2 \\ PLA: PEG 50\% D & 1.20 & 1.22 & 43.3 \\ \hline \end{tabular}
\end{table} 
Table 2: Area of characteristic NMR peaks and calculated PEG content of micromolded PLA/PEG specimens with a theoretical PEG content of 15 wt-%, 30 wt-% and 50 wt-%. P and D in the specimen name are indicated the proximal and distal part, respectively. Figure 6: FTIR spectra of PLA, PEG, and selected PLA/PEG (30 and 15 wt-% of PEG) specimens. Spectra corresponding to distal and proximal parts are displayed for the blend specimens. where \(A\) refers to the area of the indicated (subscript) NMR peak, 60 and 72 are the molecular weight (g/mol) of ethylene glycol and lactoyl repeat units, respectively. Differences between D and P parts were again minimized when the PEG load was low (e.g., 8.0 wt-% and 7.2 wt-% were determined for a load of 15 wt-%), while a difference close to 10 wt-% was observed for a 50 wt-% load. Maximum percentages were always lower than the expected value since the sprue was enriched on the less flowing polymer (i.e., PEG). Figure 8 shows the calorimetric profiles of the first heating run of the neat PLA and PEG processed specimens, and micromolded blends with different PEG contents. The PEG profile was characterized by a sharp melting peak at 67 \({}^{\circ}\)C with a high melting enthalpy that pointed out the high crystallinity that could be attained (i.e., 89.6% considering the reported value for a 100% crystalline sample, 196.8 J/g [48]). PLA profile shows a glass transition temperature with a relaxation peak at 62 \({}^{\circ}\)C and a wide cold crystallization peak over a temperature range between 95 \({}^{\circ}\)C and 140 \({}^{\circ}\)C. The enthalpy difference between the melting and cold crystallization peaks was only 0.3 J/g, indicating that PLA was practically amorphous after the micromolding processing. Features of PEG and PLA were distinguishable in the heating traces of the different blends, being possible to indicate the following points: (a) The PEG phase was crystalline being detected minimum changes in the corresponding temperature and enthalpy when the real PEG content was considered. Note that the melting peak appeared overlapped with the relaxation peak of PLA, being measurements more problematic for high PLA contents. (b) The temperature of the cold crystallization peak of PLA decreased with respect to that detected for neat PLA (i.e., from 114 \({}^{\circ}\)C to 96-98 \({}^{\circ}\)C), suggesting a nucleating effect of the PEG crystals. (c) The final melting enthalpy of PLA was lower than observed for the neat polymer even when the real PLA content in the processed samples was taken into account. This feature suggests that the presence of PEG crystals hindered the growth of PLA crystals and that a limited crystallinity could be achieved.