## 3 Results and Discussion
### Microsphere Morphological Characterization  
CMC-BTA microsphere morphology was examined by SEM and TEM. Figure 2 shows SEM micrographs of the spray-dried particles obtained using different experimental conditions, described in Table 1 (1 to 6). It is possible to observe that a spherical shape with a smooth surface was a predominant characteristic for all microparticles, regardless of the experimental parameters. The microspheres' surface smoothness, along with the absence of deposits or incrustations, suggests that the corrosion inhibitor is dispersed within the biopolymeric network.  
Such results are in agreement with the literature. Cellulose derivatives, such as carboxymethylcellulose, are common polymeric materials used in the pharmaceutical and food industries [23, 27]. The use of this class of biopolymers often results in spherically shaped particles with homogeneous surfaces [27]. Another feature that may have contributed to the formation of uniform particles, in this work, was the appropriate ratio between the encapsulated material and the encapsulating polymeric matrix (1.25:1), along with the use of poly (vinylalcohol) (PVA) as plasticizer. The addition of plasticizers is a widely used alternative to reduce fragility, and to increase the flexibility, toughness and impact resistance of polymeric films. Therefore, it is possible that PVA minimized the intermolecular interactions present in the CMC-Na network, thus increasing polymeric chain mobility and, consequently, improving the physical properties of the resulting particles [28, 29, 30, 31].  
The internal morphological structure of CMC-Na microparticles containing BTA was investigated by TEM. The results are shown in Figure 3. Conditions 1, 3 and 5 were selected to represent the three inlet temperatures tested (170, 180 and 190 \({}^{\circ}\)C) at a constant spray flow rate of 440 L/h.  
Similar to what was observed in SEM images, microcapsules with a well-defined spherical shape were found for all tested conditions. Additionally, no noticeable distinction between wall and core materials can be observed, which suggests the presence of a dense matrix-type structure (microsphere) formed by the CMC-Na polymeric network, with BTA molecules dispersed within the solid matrix. In general, particles, formed from homogeneous solutions, produced by spray drying are, according to the literature, of the matrix type [18; 32; 33]. The active material (i.e., benzotriazole) should be homogeneously distributed through the carrier polymeric matrix as previously reported by our group [16].  
Figure 3: TEM images of CMC-Na microcapsules containing BTA obtained by spray drying with different experimental conditions: (**a**) condition 1: 170 \({}^{\circ}\)C and 440 L/h; (**b**) condition 3: 180 \({}^{\circ}\)C and 440 L/h; and (**c**) condition 5: 190 \({}^{\circ}\)C and 440 L/h.  
Figure 2: SEM images of CMC.BTA microspheres obtained by spray drying with different experimental conditions (inlet temperature and spray flow rate): (**a**) 170 \({}^{\circ}\)C and 440 L/h; (**b**) 170 \({}^{\circ}\)C and 600 L/h; (**c**) 180 \({}^{\circ}\)C and 440 L/h; (**d**) 180 \({}^{\circ}\)C and 600 L/h; (**e**) 190 \({}^{\circ}\)C and 440 L/h; and (**f**) 190 \({}^{\circ}\)C and 600 L/h.