The barrier properties of flexible films play an important role in determining the shelf life of packed foodstuffs. Better knowledge of the factors governing transport properties is therefore required to improve comprehension of the phenomenon. The objective of this study is to present a 3D physically-inspired nanoscale network model for water and oxygen transport in polymeric films. The polymer, considered as a nanoporous media, is represented by a three-dimensional cubic network with randomly assigned nanopore segments and the model is solved using the Monte Carlo method (1), (2). The process is considered under isothermal conditions. As vapor flows into the polymeric film, water condensation occurs in the network nanopore walls. Liquid in the nanopore corners allows hydraulic connection throughout the network at all times and capillary pressure is determined by the augmented Young-Laplace equation. As water vapor transport occurs, water condenses by successive monolayers in the pore walls, capillary pressure decreases, and some pores are sealed for vapor transport. This phenomenon continues until the percolation threshold is reached and the film is unable to transport water vapor and oxygen. Vapor and oxygen diffusivity then decrease as vapor condensation progresses. We use experimental results for chitosan films obtained in specialized literature to validate the model. Pore throat radius is randomly assigned according to the Log-Normal pore size distribution function for chitosan film. We report nanopore-level distribution of liquid water, water vapor, and capillary pressure as transport phenomena takes place. Effective diffusivities of water vapor, liquid water, oxygen, as well as absolute permeability are calculated. Vapor and oxygen diffusivity and permeability decrease as vapor condensation occurs. On the other hand, hydraulic permeability increases as vapor condensation takes place.
Principal investigator: Prof. Luis A. Segura lsegura@ubiobio.cl
ACKNOWLEDGEMENTS
This study was financed by FONDECYT Grants 11060081and 1120347.
References:
- L.A. Segura, P.A. Mayorga, J.M. González & J.E. Paz, 2012, Latin American Applied Research, 42:185-192
- C. I. Bustos, & P.G. Toledo, 2003, Transport in Porous Media, 1773,1-35
