Poly(lactic acid) and copper-modified montmorillonite nanocomposite films for antimicrobial food packaging

Abstract

Polymer-based nanocomposites loaded with metal nanoparticles are an interesting alternative for the development of antimicrobial food packaging. However, affinity and dispersion of metal nanoparticles could be improved using nanoclays. Therefore, nanocomposite films based on poly(lactic acid) (PLA) and copper modified-montmorillonite were developed by melt-extrusion technique. Copper-modified montmorillonite at different valence states (MtCu²⁺ and MtCu⁰) were prepared. The nanocomposites were evaluated by means of their structural, optical, thermal and antimicrobial properties. Results showed that both nanoclays were intercalated in PLA but MtCu²⁺ was better dispersed. Therefore, color change ΔE < 2, higher thermal stability and higher elongation at break was evidenced for MtCu²⁺/PLA in comparison to pure PLA. Contrary, MtCu⁰ showed the displacement of Cu⁰ nanoparticles to the polymer matrix. These free nanoparticles were agglomerated and they leaded on a ΔE > 9 for MtCu⁰/PLA nanocomposites compared with PLA. Moreover, Cu⁰ nanoparticles in the matrix accelerated the thermal degradation and decreased the ductility of nanocomposites. On the other hand, both nanocomposites were able to reduce over 2 log₁₀ of Escherichia coli growth and MtCu²⁺/PLA showed a higher antimicrobial activity against Listeria innocua. These results showed the potential of nanocomposite films based on PLA and copper-modified montmorillonite for antimicrobial food packaging applications.