Supercritical CO2 Impregnation of Clove Extract in Polycarbonate: Effects of Operational Conditions on the Loading and Composition

The development of active packaging for food storage containers is possible through impregnation of natural extracts by supercritical CO2-assisted impregnation processes. The challenge of scCO2-impregnation of natural extracts is to control the total loading and to ensure that the composition of the loaded extract may preserve the properties of the crude extract. This study aimed at investigating the scCO2-impregnation of clove extract (CE) in polycarbonate (PC) to develop antibacterial packaging. A design of experiments was applied to evaluate the influences of temperature (35–60 °C) and pressure (10–30 MPa) on the clove loading (CL%) and on the composition of the loaded extract. The CL% ranged from 6.8 to 18.5%, and the highest CL% was reached at 60 °C and 10 MPa. The composition of the impregnated extract was dependent on the impregnation conditions, and it differed from the crude extract, being richer in eugenol (81.31–86.28% compared to 70.06 in the crude extract). Differential scanning calorimetry showed a high plasticizing effect of CE on PC, and high CL% led to the cracking of the PC surface. Due to the high loading of eugenol, which is responsible for the antibacterial properties of the CE, the impregnated PC is promising for producing antibacterial food containers.

Determination of CO2 solubility in semi-crystalline polylactic acid with consideration of rigid amorphous fraction

Due to phase heterogeneity in semi-crystalline polymers, accurate determination of gas solubility has been a challenge. In this regard, PLA/CO₂ was used as a case study to investigate the parameters governing formation of the rigid amorphous fraction (RAF) and its effect on the gas sorption behavior of the polymer. Six samples with different degrees of RAF were prepared through varying PLA tacticity and thermal history. Then, a gravimetric method involving a magnetic suspension balance and an in-house PVT visualization system was employed to experimentally determine the CO₂ solubility at 70 °C under a pressure of 4.5 MPa. Furthermore, a theoretical CO₂ solubility was calculated based on the Simha-Somcynski equation of state and was used in conjunction with the two-phase and three-phase models to describe the phase dependency of the gas solubility. The conventional two-phase model that considered the bulk amorphous phase consistently over-approximated the CO₂ solubility compared to the measured data. On the other hand, the three-phase model that distinguished the rigid and the mobile amorphous phases well represented the experimental result. The analysis yielded CO₂ solubility coefficients of 0.0375 g_gas/g_poly for the RAF and 0.0817 g_gas/g_poly for the mobile counterpart.