MIGRATION OF ACRYLONITRILE FROM STYRENE ACRYLONITRILE COPOLYMERS INTO FOOD-SIMULATING LIQUIDS

Correlating residual polymer concentration in polymers to the monomer migration into food simulants has been of interest for many years. Most repeated-use food-contacting articles go through multistage temperature exposures during their lifetime; therefore, the effect of varying temperature of the polymer on the migration of the monomer is of great importance in estimating the exposure of consumers to the monomer via food in contact with the polymer, in addition to the knowledge of the migration at a single temperature as has been the focus of previous studies on other polymer/monomer combinations. Studies on the migration of acrylonitrile (AN) from two styrene/acrylonitrile copolymers (SAN), one with a high melt flow which is sold into repeated use food-contact applications and one with an extremely low melt flow, show that a linear relationship exists between the amount of AN migrating from the SAN polymers into water and the square root of the time of exposure for both polymers. No difference (within estimated experimental error) was observed when the apparent diffusion coefficients obtained for the two polymers at a given temperature were compared. The data also show that a linear relationship exists between the logarithm of the AN diffusion coefficients calculated from experimental data using a simple Fickian diffusion model and the inverse of the absolute temperature of exposure. Data obtained for a two-stage temperature exposure agreed with the results obtained from an analytical solution which had previously been developed to predict the amount of monomer migrating during a multistage temperature exposure.