Supercritical CO2 sorption and diffusion in polylactic acid films: experimental study and modeling

GOÑI, MARÍA L.; SCILIPOTI, JOSÉ A.; GAÑAN, NICOLÁS A.

Los Cocos

Congreso; VI Iberoamerican Conference on Supercritical Fluids (PROSCIBA 2023); 2023

IPQA-UNC-CONICET; PLAPIQUI-UNS-CONICET

Polylactic acid (PLA) appears as a biodegradable and biocompatible alternative to petroleum based polymeric materials with several applications in food, pharmaceutical, and biomedical industries. In this sense, the incorporation of active ingredients such as drugs or natural compounds using supercritical CO2 (scCO2)-assisted impregnation technology results in an interesting strategy for developing sustainable active materials. Nevertheless, the design and modeling of impregnation processing require a deep investigation of the interaction of the different components (solute-polymer-scCO2).In the framework of a project concerning the development of PLA-based active materials, this contribution presents an experimental study of scCO2 sorption into PLA and the subsequent desorption in ambient conditions, aiming to obtain relevant equilibrium and kinetics data. For this purpose, commercial PLA films (Converflex, Argentina) and extra dry CO2 (Linde, Argentina) were used. The sorption experiments were performed in a 50 ml high-pressure vessel in batch mode [1] at different pressure (5 – 15 MPa) and temperature (45 – 60 °C) conditions. Immediately after depressurization, the desorption kinetics of CO2 from the films at ambient conditions was assessed by registering the weight loss of the CO2-swollen films using a precision digital balance (± 0.0001 g). Desorption curves were extrapolated in order to obtain equilibrium sorption data.PLA showed a high scCO2 sorption capacity, obtaining values up to 17 wt% when low temperature and high-pressure conditions were used (45°C and 15 MPa), which indicates that sorption is extremely related to scCO2 density. Experimental sorption equilibrium data were modeled with the Sanchez-Lacombe equation of state (SL-EOS) [2], using characteristic properties for PLA and CO2 taken from the literature after a comparative analysis of reported values, and fitting the binary interaction parameter kij to minimize the CO2 chemical potential difference in both phases.A Fickian mass transfer model for non-steady diffusion in thin slabs was fitted to the experimental desorption kinetics data, in order to estimate scCO2 apparent diffusivity on PLA (Da) at ambient conditions. A good correlation with the initial amount of CO2 in the polymer was obtained, observing an exponential dependency of Da with the sorption values.The high scCO2 sorption capacity of PLA suggests an important swelling degree of this polymer, which was also observed and reported by other authors [3]. In a ternary system, swelling allows a faster solute diffusion through the polymer matrix which favors the impregnation process. In this sense, PLA can be considered an attractive material for this kind of process. Finally, the SL-EOS model was successfully fitted for the [scCO2-PLA] binary system, as a previous step for the predictive modeling of different [solute-PLA-scCO2] ternary systems.