2 - Mass transfer of gas and solute through packaging materials

Abstract

This chapter reviews mass transfer phenomena and defines the diffusivity, permeability, solubility, and partition coefficient of transferring molecules. Gases and solutes are considered separately. There are many applications in the area of food packaging that use mass transfer phenomena. Permeation, absorption, and diffusion are typical mass transfer phenomena occurring in food packaging systems. Permeation is the ability of permeants to penetrate and pass through an entire material in response to a difference in partial pressure—the gas and water vapor transmission rates of packaging materials give a good indication of permeation. Thus, the mass transfer coefficient for permeation is permeability. The mass transfer of a solute from a solution through a (polymeric) material is also a useful way to determine mass transfer coefficients experimentally, because it requires simple permeation apparatus (i.e., a permeation cell) consisting of the high and low concentration solution chambers divided by the test film material. Diffusion is the movement of a diflfusant in a medium caused by a concentration difference acting as a driving force. Diffusivity is a measure of how well the compound diffuses in the medium. Absorption and its counterpart desorption measures the affinity of a given substance for two media with which it comes into contact. The permeability, solubility, and diffusivity have characteristic values for a migrating component through a particular medium. These parameters are therefore essential in simulating the mass transfer profile.