Two-phase molecular dynamics model to simulate the migration of additives from polypropylene material to food

Abstract

Migration of chemical additives from polypropylene material to food simulants (50% ethanol solution and isooctane) at the temperature of 293, 313 and 343 K are investigated by using molecular dynamics (MD) simulation technique based on the classical mechanics. A two-phase MD model is firstly established to simulate the migration dynamic process. The migration dynamic details are obtained, especially for the significant kinetic parameter of diffusion coefficient. The accuracy of MD simulation is assessed by comparing the diffusion coefficients obtained by MD simulations, experiments and Piringer model. It is indicated that the diffusion coefficients of additives obtained from two-phase MD model are generally within one order of magnitude of the corresponding experiments. The two-phase MD model of polypropylene – food simulant offers fairly good predictive ability, which means MD simulation technique is a powerful way to predict the migration process and level of additives from polypropylene material to food. In addition, different influencing factors for additive migration are examined including the additive molecular structure, interaction energy between additive molecule and polypropylene, food simulant and temperature. The movement trajectories of additives in polypropylene – food simulant cells at different simulation time suggest that the additive molecules vibrate rather than hopping for a long time, until they find the equal or larger transport channel to diffuse.