Montmorillonite nanoclay based formulation for controlled and selective release of volatile essential oil compounds

In the current study, a green method that can be easily used in different industrial applications, based on the modification of sodium exchanged montmorillonite (Na+-Mt) with essential oils (EO) such as thyme oil, thymol and carvacrol was presented. The obtained results show the prepared clays-essential oils hybrids were promising nanomaterials to encapsulate the active compounds and to control their release selectively in the functional applications. X-ray diffraction (XRD) analysis was used to study the adsorption of EO, thymol and carvacrol molecules, in the interlayer space. To verify the adsorption of thyme EO, thymol and carvacrol into Na+-Mt layers and to determine the temperature range where the EO, thymol and carvacrol release took place, thermogravimetric analysis (TG) was used. Attenuated total reflecting-Fourier-transform infrared (ATR-FTIR) spectroscopy was used to verify and to study the adsorption mechanism. The obtained results show that the interlayer space of Na+-Mt was not affected by the adsorption of thyme EO, thymol or carvacrol molecules. The release of the adsorbed molecules of thyme EO, thymol or carvacrol from Na+-Mt surface was obtained above 180 °C. Combination of simulation with all obtained experimental results, confirm that the adsorption process of thyme EO, thymol, and carvacrol molecules on the Na+-Mt took place on the external surface i) by hydrogen bonds between the OH groups of thyme EO, thymol or carvacrol molecules and OH groups of Na+-Mt surface, and ii) by hydrogen bonds between these adsorbed molecules. The release study shows that the adsorption of EO like thyme, and its constituents such as thymol and carvacrol onto an inorganic porous material such as Na+-Mt provides extended controlled release of all adsorbed active molecules with their chemical stability due to the protection against environmental conditions. In addition, the release of thyme oil constituents (like thymol and carvacrol) occurs by a selective process in time.