Micromeritic properties of sulfamethoxazole microcapsules prepared by gelatin–acacia coacervation

Micronized sulfamethoxazole particles were microencapsulated using the gelatin–acacia complex coacervation method. The effects of the coacervation pH and the amount of formaldehyde used on the micromeritic parameters of the microcapsules were investigated. The particle-size and the wall thickness distributions were log-normal forms. As the pH was increased, the particle size decreased (8.5–28.5 μm). The porosity of various pH-adjusted microcapsules was between 0.158 and 0.277. The particle size of formalized microcapsules was larger than that of the unformalized microcapsules because formalization prevents shrinking of microcapsules during the dehydration and drying process. A smooth surface appeared on the unformalized microcapsule, but a net-like wrinkled structure was observed upon scanning the formalized one. Moreover, folding and invaginating structures were found on the spray-dried microcapsules. The optimum coacervation pH value was 3.5, at which the highest core content was obtained (77.5% w/w). Approximately 6.73 μg of formaldehyde remained in 1 g of the microcapsules formalized with 50 ml of formaldehyde. The crystalline sulfamethoxazole in the microcapsules prepared by spray drying the coacervate slurries was changed into the amorphous form, while the microcapsules dried in the conventional manner showed the same sulfamethoxazole form as the starting substance.