Kinetic Analysis of Lactic Acid Release From Polylactic Acid (PLA) Films in Aqueous, Ethanolic, and Acidic Media

Abstract

This study investigated the migration kinetics of lactic acid from polylactic acid (PLA) films into three food simulants—10% ethanol, 3% acetic acid, and 95% ethanol—at 20, 40, and 60°C. Lactic acid was quantified using high-performance liquid chromatography (HPLC), and migration data were fitted using Fick’s second law to estimate diffusion and partition coefficients. At 20°C, 95% ethanol exhibited the highest migration, indicating greater release of lactic acid from the PLA matrix. At elevated temperatures (40–60°C), migration increased in 10% ethanol and 3% acetic acid, with hydrolytic degradation becoming more pronounced at 60°C, particularly in the acidic simulant. In contrast, 95% ethanol showed distinct migration behavior, likely due to the combined effects of ethyl lactate formation and changes in the thermal and crystalline properties of PLA. The diffusion model showed good agreement with experimental data, describing time-dependent migration and equilibrium behavior. However, deviations at elevated temperatures in aqueous and acidic media indicated non-Fickian behavior associated with PLA degradation. All migration levels remained well below the regulatory limit of 10 mg/dm². These findings highlight the importance of environmental conditions in PLA-based packaging and provide a predictive framework for assessing migration behavior in food contact applications.