## 3 Results and Discussion
### Thermal Analysis
#### 3.3.3 Filament Extrusion and 3D Printing  
The aim of blending poly(S-_co_-MMA) with amorphous PLA was to evaluate the material under processing conditions for filament production and additive manufacture (see Figure 7). Additionally, the methodology was developed specifically for the amorphous PLA, obtaining blends with improved properties. In general, these blends present similar \(E\) to the poly(S-_co_-MMA); however, a decrease in the elongation at break and tensile strength were observed. However, the best polymer blend was PLA\({}_{90}\)/poly(S-_co_-MMA)\({}_{10}\) concerning the \(E\).  
Moreover, the three filaments of PLA\({}_{\rm x}\)/poly(S-_co_-MMA)\({}_{\rm y}\) blends were produced via extrusion. The extruder at the prototype level was designed with two heating zones, as follows: The first zone was a pre-heating of the feed polymer blend until 150 \({}^{\circ}\)C, and the second had a thermal resistance in the extrusion die at 195 \({}^{\circ}\)C to avoid thermal degradation of the blends. The screw speed was established between 20-40 rpm as a limit for obtaining 1.75 mm filament diameter, according to the experimental values reported by [PERSON] et al. [8]. The filament diameter was 1.75+/-0.03 mm of standard deviation.  
The PLA\({}_{90}\)/poly(S-_co_-MMA)\({}_{10}\) blend was selected to show the 3D printing process in the present research. A uniform 1.75 mm diameter was reached; this size was reported by other authors [24; 76]. Nevertheless, another 1.6 mm diameter was reported for PLA-hydroxyapatite filaments [21]. The printing temperature is typically set between 180-240 \({}^{\circ}\)C for blends and composites having PLA as the matrix. For example, in a few investigations, 210 \({}^{\circ}\)C were used when printing PLA [21; 77], but also, a 190 \({}^{\circ}\)C lower temperature was set in another analysis [76].  
The proper filament was charged to a CTC 3D printer. Parameters were set (Table 2), such as temperature and feed rate printing, a cube 1 cm \(\times\) 1 cm \(\times\) 1 cm for probes. The temperature variable was analyzed from 195 to 210 \({}^{\circ}\)C, where at 210 \({}^{\circ}\)C, the 3D printing piece presented melted layers with a 35 mm/s feed rate. The behavior at 200 \({}^{\circ}\)C was improved in the printing piece. Finally, an optimal piece was obtained at 195 \({}^{\circ}\)C, and at a 40 mm/s feed rate. A small 2 cm cube was used as a model (see Figure 8d). In addition, the parts manufactured for mechanical analysis through compression molding, polymeric filament via extrusion, and 3D printing by means of FDM do not undergo changes color whenever compared. Therefore, although there is slight thermal degradation in the blends, the parts do not have yellowing in the final product.  
Figure 8: Filament extrusion and its 3D printing of PLA\({}_{\text{w}}\)/poly(S-\(\alpha\)-MMA)\({}_{\text{y}}\) blends. (**a**) Filament extrusion level prototype. (**b**) Scheme of filament extrusion. (**c**) 3D-printing. (**d**) Some parts manufactured through compression molding (probes), filament extrusion, and 3D printing, comparing their color.  
Figure 7: Scheme of the filament extrusion and 3D printing process. (**a**) Screw, barrel, and housing manufacture. (**b**) 3D printing.