Title : Production and characterization of gellan aerogel macrospheres using supercritical CO2 drying
Aerogels are a class of new materials, which have high porosity and surface area, and low density. Polysaccharides based aerogels have potential application in food, biomedical, and pharmaceutical applications due to them biodegradability, loading capacity of target compounds and controlled release. Based on that, the purpose of this work was to produce and characterize gellan aerogel macrospheres using supercritical CO2 drying. Solutions of gellan were prepared at 0.5, 0.75 and 1% (w/w) and heated for 30 min at 900C. CaCl2 solutions were used as crosslinking agent ranging the ionic strength (0.03, 0.06 and 0.09 M). Then, the polymeric solution was pumped (1 mL/min) and dripped through a nozzle (0.58 mm) into the crosslinking solution. Once gelled the macrospheres were collected and subjected to solvent exchange, in which they were progressively immersed into ethanol/water mixtures (10, 30, 50, 70, 90 and 100%, v/v) for one day, except the last step that was repeated three times. Finally, the macrospheres were dried with a continuous supercritical CO2 flow at 40±1 °C and 12±0.5 MPa. The surface and shape of the hydrogel, alcogel and aerogel particles were examined by electron microscopy, and the data were processed by ImageJ image software. The reduction of the particle size between the processes was calculated and expressed as relative shrinkage. The hydrogel macrospheres presented drop shape, and the circularity was 0.81±0.04. The increase of gellan concentration increased de hydrogel macrospheres size, which ranged from 2.30±0.03 to 2.90±0.03 mm. The overall shrinkage (0.69-0.79) decreased as the gellan content increased. The aerogel macrospheres size ranged from 1.15±0.02 to 1.519±0.10 mm. Supercritical drying is considered the best option for obtaining aerogel. Nevertheless, the shrinkage was larger than the observed in aerogels from other polymers. So, the study of techniques to reduce the gellan aerogel shrinkage is considered perspective for further works.