Modelling dynamic changes in headspace gas composition

Headspace gas composition changes dynamically due to several factors. Gas exchange with the enviromnent occurs over the packaging film if the partial pressure of a gas differs on the two sides of the film. The amount of gas that permeates the film can be calculated from equation 9.1 (Robertson, 1993)  

Ap = the difference in gas partial pressure on the two sides of the film (atm) t = the storage time (24h) 

Different gases have different permeability through the same film. For conventional films, the permeability of CO2 is generally 4-6 times larger than 

Permeability is also influenced by storage temperature and relative humidity. Pfeiffer et al. (1999) found that the empirical equation 9.2 fitted well with published data for oxygen permeability. 

Gas exchange over the packaging film is of particular importance when the film needs to maintain a narrowly defined gas concentration, as shown in the example in Section 9.5, where the permeability of even small amounts of O2 into a package containing a cured meat product is considered a critical packaging parameter. 

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