Estimation of allowable styrene concentration in polymer

Given the acceptable threshold concentration for styrene in a given product, one can calculate a maximum acceptable initial concentration of residual styrene in the food contact material (QMcaic). Cp, is replaced with the threshold concentration (TC) in Eq. (14-4) to yield Eq. (14-8) or cf oc is replaced with TC in Eq. (14-3) to yield Eq. (14-9). 

As long as the initial concentration, cpo, of styrene in the material is not larger than the largest QMcalc value calculated from Eq. (14-8) or (14-9) the taste threshold in the product will not be exceeded. 

Example 14-5 Calculate the maximum allowable amount of styrene monomer (Mr = 104.2) that can be allowed in a PS thermoformed portion pack with foil lid (7.5 g product) for condensed milk (see Example 14-1). Assume that based on experience a concentration above 300 pg/kg in the product will produce an off-flavor and lead to consumer complaints. The package surface area to food mass ratio ( ) is jf = 1.5 cm2 g . The product is shelf stable and has an intended shelf life of 6 months. 

4) Compare this with the mass balance result using Eq. (14-9) (in a high fat product one can 

Diffusion controlled migration results in step 3 compared to the results in step 4 assuming a mass balance, show that the diffusion of the styrene in the polymer acts to slow down mass transfer into the product. These calculations also show that the relationship in Eq. (14-1) is still valid (mass balance calculations represent the maximum possible amount of migration). 

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