Characterizing the migration of antioxidants from polypropylene into fatty food simulants.

The migration (diffusion and equilibrium) processes of antioxidants (AOs) from polypropylene (PP) films of different thicknesses into n-heptane and 95% ethanol as fatty food simulants were analysed at 20, 37 and 60 degrees C. Heptane fully extracted the AOs from the polymer while a partition equilibrium described the migration to ethanol. The kinetics of migration were also studied via the diffusion coeffcients. As expected, diffusion was found to be faster when the polymer was in contact with heptane, due to polymer swelling by the solvent. The kinetics of the process in ethanol was described by different theoretical expressions which are discussed. Equations disregarding partition equilibrium failed to describe the process and the diffusion coefficient values obtained through them were much smaller than the actual ones and dependent on film thickness. The results also showed the significance of food simulant selection in the analysis of food-packaging interactions and migration variability with thickness.

Global and specific migration of antioxidants from polypropylene films into food simulants.

Global migration and specific migration of antioxidants (AOs--Irgafos 168 [tris(2,4-di-tert-butylphenyl) phosphite], Irganox 1076 [octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl-propionate], and Hostanox SE2 (distery thiodipropionate)--from polypropylene (PP) films into food simulants (water, 3% acetic acid, 95% ethanol, olive oil, and heptane) were studied. Films (50, 100, and 200 microns thick) were exposed to simulants at temperature-time conditions simulating migration under retorting and long-term storage. Global migration into aqueous simulants was independent of film thickness and conditions of exposure, so it seems as if the migration process was limited to the dissolution of migrants on the contacting surface. Global migration to fatty food simulants was dependent on simulant, conditions of exposure, and in some cases film thickness. Specific AO migration was analyzed from dry residues obtained from global migration analysis. Migration of AOs into aqueous simulants was below the detection limit (0.01 mg/dm2). Migration into fatty food simulants was dependent on the simulant. The extractive power of simulants was similar to that observed in global migration studies. Specific migration into heptane was independent of the polymer mass, though dependent on the thickness. Migration into ethanol was dependent on both mass and thickness. A theoretical discussion about the controversial effect of thickness on migration results, based on the kinetics of the process, is presented.

Analysis of antioxidants extracted from polypropylene by supercritical fluid extraction.

Maximal potential migration of six antioxidants (AO) from five polypropylene (PP) formulations was determined by two supercritical fluid extraction (SFE) procedures, both of which contained static and dynamic steps. All analytical conditions affecting the extraction were studied and optimized using Irgafos 168 as standard. SFE was more efficient as temperature and fluid density increased. During the static step in which the samples were exposed to the fluid without flux, the introduction of hexane and methanol as fluid modifiers significantly improved the extraction. Hexane appears to facilitate polymer swelling while methanol solvates the antioxidants. In the dynamic step (in which the extraction actually occurs) time is the key parameter. Extraction for 90 min results in an efficiency of around 75%. The introduction of modifiers during this step (by an HPLC-SFE procedure) did not produce any significant improvement. When SFE was carried out on all samples, extraction efficiency was around 75% except for Irganox 1010 and Hostanox O3. The large molecular volume of these antioxidants may be responsible for the considerable reduction of extraction efficiency. Particle size and shape of polymer sample were also important. The greater the surface to volume ratio the greater the extraction efficiency.