Impregnation of cellulose acetate with natural bioactive compounds using supercritical carbon dioxide

Abstract

Porous acetate cellulose (CA) beads were tested as carriers for thymol, eugenol and carvacrol, natural compounds well known for their biological activity. For this purpose, selected compounds were impregnated into CA using the environmentally friendly medium, supercritical carbon dioxide (scCO2). Firstly, impregnation of CA with thymol was tested in the pressure range of 10, 15, and 20 MPa for 2 and 24 h at a temperature of 50 °C. The pressure increase resulted in only slight increase in thymol loading. On the other hand, an increase in operating time at 10 MPa resulted in increase in thymol loading from 4.6 to 66.2%. Following the obtained results, subsequent experiments of CA beads impregnation with eugenol and carvacrol were performed at 10 MPa during 2 h, achieving amounts of loaded eugenol and carvacrol of 1.33 and 4.6%, respectively. The presence of thymol, eugenol and carvacrol on/in CA beads as well as its interaction with polymer was confirmed by the FTIR analysis. SEM images revealed that the porous structure of CA beads remained unchanged after its exposure to neat scCO2. However, loading of CA with thymol, eugenol and carvacrol at selected conditions led to the slight change in material texture and morphology. This observation was further examined using mercury intrusion porosimetry. While neat CA had an average pore diameter of 286 nm and porosity of 58%, loaded CA beds expressed an overall reduction in these values. The results were in line with the amounts of loaded active compounds. Namely, for the higher amount of loaded active substance, the higher decrease of specific surface area was observed. These results gave the guidelines for an effective functionalization of neat CA with compounds that have pronounced antimicrobial and antioxidant activity.