Development of an integrated one-pot process for the production and impregnation of starch aerogels in supercritical carbon dioxide
Maria Villegas, Alessandra L. Oliveira, Reinaldo C. Bazito, Pedro Vidinha
The aim of the present work was to develop a one-pot process for the fabrication and impregnation of starch aerogels with green coffee oil (GCO). To accomplish this, several modifications were made on the fabrication process in order to integrate gelatinisation, retrogradation and drying with the impregnation process. Therefore, a different drying approach based on supercritical extraction (SCE) was proposed, as well as the fabrication of starch aerogels in the presence of CO2. The obtained materials were initially used for the impregnation of GCO using supercritical CO2 (scCO2). The integration of the all the above steps led to the development of a one-pot concept that allowed the fabrication and the impregnation of starch aerogels.
The first step consisted of the development of a drying process that did not required any solvent-exchange process. The results show that by using a continuous flow of CO2/ethanol (200 bar, 40 °C, 2 mL/min CO2 with 11% ethanol) was possible to obtain starch aerogels exhibiting high surface area (almost 95 m2/g). This approach allowed not only an important reduction in drying time (6 h) when compared with literature (nearly 24 h) but also the elimination of the solvent exchange process. The next step comprised the formation of starch aerogels in the presence of CO2. Therefore, the impact of CO2, temperature and starch concentration was evaluated on the physicochemical properties of the obtained materials. The results show that is possible to obtain high-surface-area materials using this strategy and that CO2 has a positive impact on both gelatinisation and retrogradation steps. The best materials produced in the presence of CO2 exhibited a surface area of 185 m2/g, which agrees with the highest values reported in the literature. The final step consisted of the impregnation of the obtained materials with GCO. The results show that the best conditions for this impregnation were achieved at 300 bar and 40 °C for 12 h. The impregnation efficiency was 39%, which is in line with the literature values reported for this type of material.
Finally, the integration of gelatinization, retrogradation, drying and impregnation was achieved. All these steps took place in the same reaction vessel following a sequence of steps that allow the production of starch aerogels containing GCO. The results show that the one-pot strategy produces positive results, since it achieved an impregnation efficiency of 24%, which is an encouraging result and open new doorways for the application of this concept.