Assessment of kinetic release of thymol from LDPE nanocomposites obtained by supercritical impregnation: Effect of depressurization rate and nanoclay content

LDPE nanocomposites prepared with different concentrations of an organo-modified montmorillonite (OM-MMT) (2.5 and 5.0% (w/w)) were impregnated with thymol using supercritical carbon dioxide, with the aim of obtaining an antimicrobial packaging. Impregnation assays were carried out at 12 MPa, 1 h, 313 K and two depressurization rates, 10.0 and 1.0 MPa min(-1), with impregnation yields in the range of 0.36-1.19% (w/w). The highest incorporation percentages of thymol were obtained employing the lowest depressurization rate. Moreover, thymol incorporation was favored with the presence of nanoclays. XRD results indicated the improvement of nanocomposites intercalation impregnated with thymol. Simultaneously, a phenomenological mass transfer model has been used to describe the release of thymol from the nanocomposite in ethanol 95% (v/v) solution. From the model, the effective diffusion coefficient of thymol through the nanocomposite seem to be independent of the depressurization rate employed. These values were ranged from 2.7 to 3.5 x 10(-13) m(2) s(-1) and are significantly lower than the values obtained for free nanoclay LDPE films, which shows values ranged from 1.0 to 1.3 x 10(-12) m(2) s(-1). This result could be explained by the formation of a polymer-nanoclay intercalated structure that slows down the thymol transfer.