## 3 Results and Discussion
### BTA Release Studies from Carboxymethyl Cellulose Microspheres
#### 3.5.2 Release Studies  
Release studies were performed in an aqueous medium, since water is present in most of the environments where coated metallic structures are exposed. It is worth mentioning that water contact with a metallic substrate will only occur if there is a failure in the protection barrier system (organic coating). Moreover, water is also involved in the most common mechanisms of metallic corrosion, i.e., corrosion in aqueous media. Typically, when exposed to service life conditions, a coated metallic structure will be subjected to different weather conditions, such as temperature gradients, electromagnetic radiation, water, salts and other contaminants, as well as mechanical actions (e.g., scratch induced chipping). Overall, this will contribute to coating degradation, creating pathways that will allow water, O\({}_{2}\) and ions to reach the metal substrate and initiate the corrosion processes. Therefore, since water inlet is one of the first steps associated with onset of corrosion, the incorporation of materials in coatings that will respond to the presence of water and readily release corrosion inhibitors can be important to provide long-term protection when coatings start to fail. One example of such a material is CMC-Na microparticles. In this system, water molecules are absorbed by the hydrophilic biopolymeric network, and the encapsulated material swells, forming a gel that allows the release of the encapsulated material from the CMC-Na matrix [41]. The cumulative amount (%) of BTA released from CMC.BTA microspheres as a function of time is displayed in Figure 4.  
In general, all of the release profiles show similar behavior for all of the microparticles tested. (UV-Vis measurements of empty CMC-MS for every spray drying condition, were performed, and no absorbance was observed; therefore, CMC-MS does not interfere with BTA release data.) A high burst release of BTA was observed after 5 min of immersion with values ranging from 40 to 90% of the total loading content. Although this behavior can be associated with the hydrophilic nature of the biopolymeric matrix, which allows the permeation of water and consequent release of the encapsulated material, it is possible to observe an undoubtable influence of the spray drying parameters on the release profiles. There is an accentuated increase in the amount of BTA released in the burst phase as the inlet temperatures increase. Moreover, an increase in the spray flow rate, for the same inlet temperature, leads to an increase of 22 and 9% in the burst release for 170 \({}^{\circ}\)C and 180 \({}^{\circ}\)C, respectively, and a smaller, less noticeable 3% increase for a 190 \({}^{\circ}\)C inlet temperature. In what concerns the experiments conducted at 170 \({}^{\circ}\)C (conditions 1 and 2), after the initial burst release, there is a gradual and more controlled release of the remaining BTA up  
Figure 4: BTA release behavior from CMC.BTA microspheres, obtained by spray drying at: (**a**) 170 \({}^{\circ}\)C; (**b**) 180 \({}^{\circ}\)C and 440 L/h; and (**c**) 190 \({}^{\circ}\)C. Spray flow rates 440 L/h (closed) and 600 L/h (open). to 72 h, where a plateau is reached, assumed as the total release of the encapsulated inhibitor. Similar behavior was observed for particles produced at 180 \({}^{\circ}\)C (conditions 3 and 4), although a pronounced increase in release after 1 h leads to a complete release by 4 h of immersion, instead of the 72 h previously identified. A drastically different release profile was obtained for conditions 5 and 6 (190 \({}^{\circ}\)C) where the burst release phase leads to an almost complete release (89-92%) of the encapsulated BTA in the first 5 min of immersion. Similar release profiles have been described in the literature. [PERSON] et al.