## 3 Results and Discussion
### Thermal Analysis
#### 3.3.2 Thermogravimetric Analysis  
Figure 6 displays thermogravimetric mass loss and derivative mass loss (DTG) curves of neat PLA, neat poly(S-_co_-MMA), and PLA\({}_{\text{x}}\)/poly(S-_co_-MMA)\({}_{\text{y}}\) blends. Furthermore, a particular behavior was observed in all blends presenting at least two degradation stages regarding a mass loss. For example, the PLA\({}_{\text{50}}\)/poly(S-_co_-MMA)\({}_{\text{50}}\), in Figure 6a, presented a first mass loss stage of 96.8% between 321.4 and 420.8 \({}^{\circ}\)C, and a second step losing 3.0% over 420.8 until 490 \({}^{\circ}\)C. Correspondingly, there are three peaks in the DTG curve; one is located at 351 \({}^{\circ}\)C, followed by a second one maximum degradation temperature (T\({}_{\text{max}}\)) = 358.6 \({}^{\circ}\)C, and lastly, a small peak at 488 \({}^{\circ}\)C. Similarly, the PLA\({}_{\text{75}}\)/poly(S-_co_-MMA)\({}_{\text{25}}\) blend in Figure 6b displayed a peak with T\({}_{\text{max}}\) = 325.1 \({}^{\circ}\)C, and two shoulders placed next to the central peak with a mass loss of 16.4% from 343.6 to 400.1 \({}^{\circ}\)C, according to DTG and mass loss, respectively. The mass loss in the first event was about 80.8% between 255 and 343.6 \({}^{\circ}\)C. A third stage was also observed over 400.1 \({}^{\circ}\)C, with a mass loss of 1.8%. Concerning the DTG curve of the PLA\({}_{\text{90}}\)/poly(S-_co_-MMA)\({}_{\text{10}}\) blend, Figure 6c shows one peak with T\({}_{\text{max}}\) at 334.3 \({}^{\circ}\)C and another at 368.5 \({}^{\circ}\)C. In addition, the first mass loss was observed from 250.1 to 345.6 \({}^{\circ}\)C, losing about 87.8%. The next stage of mass loss was of 9.4% between 345.6 and 388.6 \({}^{\circ}\)C. The last stage was presented at over 388.6 \({}^{\circ}\)C, with a mass loss of 2.0%. Additionally, the degradation stages of the PLA\({}_{\text{x}}\)/poly(S-_co_-MMA)\({}_{\text{y}}\) blends can be attributed to PLA degradation by hydrolysis during the process [65; 66]. In addition, the chemical structure of poly(S-_co_-MMA) can decrease the thermal stability due to the presence of double carbon bonds and aromatic rings, according to [PERSON] et al. [67]. Furthermore, the poly(S-_co_-MMA) had a thermal decomposition stage from 260 to 460 \({}^{\circ}\)C and a T\({}_{\rm max}\) around 378 \({}^{\circ}\)C (Figure 6d). Figure 6e displays a single degradation step for PLA with a T\({}_{\rm max}\) at 352.9 \({}^{\circ}\)C [50]. On the other hand, these results agreed with other publications that studied blends or composites of PLA, poly(S-_co_-MMA), PS, or PMMA. For instance, [PERSON] et al. [68] reported an initial decomposition temperature for poly(S-_co_-MMA) at 260 \({}^{\circ}\)C. In addition, [PERSON] et al. [69] reported three thermal decomposition stages from 360 to 474 \({}^{\circ}\)C for poly(S-_co_-MMA), owing to individual functional group decomposition. Likewise, it was observed that PLA/PS blends two different stages attributed to the semi-crystalline and amorphous structures for PLA and PS, respectively [70]. Similarly, [PERSON] et al. [71] studied the thermal decomposition of PLA/PMMA blends with or without flame retardant, finding a displacement in PMMA T\({}_{\rm max}\) from 379 \({}^{\circ}\)C to 430 \({}^{\circ}\)C when the mixture contained flame retardant. However, [PERSON] et al. [72] decreased the PLA T\({}_{\rm max}\) from 362 to 315 \({}^{\circ}\)C when incorporating phosphorus as flame retardant (5 wt.%) into PLA/PMMA blends. Finally, [PERSON] et al. [73] added poly(styrene-_co_-glycidyll methacrylate) P(S-_co_-GMA) to a PLA\({}_{80}\)/PMMA\({}_{20}\) blend improving thermal stability with the copolymer at 3 ppb. Moreover, the blends' thermogravimetric curves established the conditions of thermal stability during the process of filament extrusion and 3D printing. The mass loss percentage at 195 \({}^{\circ}\)C for PLA\({}_{50}\)/poly(S-_co_-MMA)\({}_{50}\), PLA\({}_{75}\)/poly(S-_co_-MMA)\({}_{25}\), and PLA\({}_{90}\)/poly(S-_co_-MMA)\({}_{10}\) were 0.03, 0.10, and 0.19%, respectively.