Experimental and Theoretical Study on Specific Migration in Plastic Films: Effect of the Thickness and the Antioxidant Concentration

摘要

This work presents a theoretical and experimental study on the specific migration process, describingthe mass transfer of a model migrant Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox1076). Film samples (LDPE), with initial concentration of Irganox between 1000 and 6000 (mg/kg), thicknessof 50-190 mm, were placed in contact with fatty (ethanol 95%) and aqueous (ethanol 10%) food simulants at40℃ for 20 days, gathering samples of simulant at different times in order to obtain the concentration evolutionin the food simulant which was measured by HPLC. A phenomenological model based on a resistancesin-series approach was developed considering the diffusion through the polymer film, natural convection inthe food simulant and the thermodynamic equilibrium between the polymer and the liquid simulant phase.The value of the partition coefficient is introduced in a Matlab program that solves the mass transfer model bymeans of the iterative Regula Falsi method. For the thickest films, the diffusion coefficient values was estimatedvarying between 1.95×10-13 (m2 s-1) and 2.0×10-13 (m2 s-1) at 40 ?C. On the contrary, the thinnest oneshows a significant decreasing of the diffusion coefficient value, which was evaluated in 1.0×10-14 (m2 s-1).This modification can be explained by means of a crystal distribution and size in the thinnest polymer filmprepared by CAST extrusion.