Prediction of partition coefficients of plastic additives between packaging materials and food simulants
Résumé
Partition coefficients, K(i,F/P), between liquids or food simulants, F, and amorphous regions of polymers, P, are important quantities to predict the sorption or desorption kinetics in various areas and in particular to predict the contamination of food by substances originating from food contact materials. This work extends an atomistic Flory-Huggins approach previously developed by us (Ind. Eng. Chem. Res 2009, 48, 5285-5301) to predict K(i,F/P) values for large solutes such as antioxidants, light stabilizers, and surface agents. Two extensions were particularly considered. The first extension aims at determining by isobaric molecular dynamics (MD) simulation the contribution of translational entropy in liquids with increasing polarity (isopropanol, ethanol, methanol, ethyl acetate, water) for large and flexible solutes representative of plastics additives. It was found to be higher than the partial molar volume of such solutes, independent of the considered alcohol and satisfactory estimated by the volume accessible to a hydrogen probe. The validity of the coarse-graining approximation for large flexible solutes (octadecane and octacosane) was tested by computing the radial distribution function from MD simulations. A simple correction was proposed to account for the partial overlapping at the coarse-grained level between F molecules and large flexible segments of solutes. The second major improvement extends the whole methodology to water and water ethanol mixtures. Intrinsic limitations of the Flory-Huggins approximation to handle hydrogen bond cooperativity were overcame by reweighting contact energies in water and by introducing tabulated nonideal properties of water ethanol mixtures. All predictions agreed well with previously published partitioning data as well as those generated by this study. From experimental values and theoretical considerations, the possibility to predict the contamination of food emulsions with water ethanol mixtures is finally discussed.