Development of long-term antimicrobial poly (ε-caprolactone)/silver exchanged montmorillonite nanocomposite films with silver ion release property for active packaging use

Poly (epsilon-caprolactone)/silver exchanged montmorillonite (PCL/Ag-MMT) nanocomposites with a strong antibacterial activity and a slow release property were successfully prepared via solvent casting method, for active packaging use. The PCL/Ag-MMT nanocomposites containing different Ag-MMT loadings were characterized by several techniques. X-Ray Diffraction (XRD), UV-visible Spectroscopy and Transmission Electron Microscopy (TEM) results revealed that the MMT layers were exfoliated and spherical Ag nanoparticles were randomly distributed in the polymer matrix. Differential scanning calorimetry (DSC) showed that glass transition and melting temperatures of PCL/Ag-MMT nanocomposites were unaffected by clay contents compared to neat PCL. Nevertheless, the crystallization temperatures were increased due to the incorporation of effective nucleation agent Ag-MMT and its satisfactory dispersion into the PCL matrix. The positive effect of the Ag-MMT addition on the PCL barrier properties was confirmed by the reduction in the water permeability (WVP). Tensile results also displayed an improvement of mechanical properties for the PCL/Ag-MMT nanocomposites due to the insertion of clay particles into the PCL matrix. The potential of the silver ion release from the PCL/Ag-MMT films to a slightly acidified water medium was measured by atomic absorption spectroscopy. The results exhibited a gradual increase of the amount of silver ions released up to 30 days of immersion. The kinetic study of the ions release showed that the release's mechanism is governed by the diffusion process. The apparent diffusivity coefficient values calculated using the diffusion model were in the range of 3.8 x 10(-10) to 5.8 x 10(-10) cm(2)/s. Furthermore, the PCL/Ag-MMT films exhibited a strong antibacterial efficiency against S. aureus, E. coli, salmonella and P. aeruginosa due to the presence of the long-lasting biocidal silver nanoparticles.