Release of thymol from poly(lactic acid)-based antimicrobial films containing kenaf fibres as natural filler

- The migration of thymol from poly(lactic acid)/kenaf fiber composites into ethanol solutions was investigated.
- The release of thymol was described by first-order kinetics and diffusion models.
- The release was faster in higher ethanol content simulants.

The migration of thymol, a natural antimicrobial (AM) substance, from poly(lactic acid) (PLA) films containing 300 g/kg kenaf fibres into food simulants is reported. Neat PLA and PLA/kenaf films containing 100 g/kg thymol were prepared via melt blending and heat pressing and were placed in contact with 150 mL/L and 950 mL/L ethanol/water mixtures at different temperatures. First-order kinetics, diffusion modelling and Fick's law modelling were used to describe the release. The release rate of thymol into 950 mL/L ethanol/water at different temperatures displays Fickian behavior with diffusion coefficient values between 1 and 100 × 10−11 m2 s−1 with close to 100% of thymol being released. The release rate of thymol is temperature dependent and is affected by the percentage of ethanol in the simulant. In the case of neat PLA and PLA/kenaf films, a faster release occurred in 950 mL/L ethanol/water than in 150 mL/L ethanol/water with the composite film exhibiting a higher diffusion coefficient in each case.