Antibacterial LDPE-based nanocomposites with salicylic and rosmarinic acid-modified layered double hydroxides

Polymer nanocomposites, prepared by dispersing layered nanofillers bearing active and natural compounds in a polymer matrix, offer a tunable way to confer antibacterial activity to traditional polymers for packaging materials. Antibacterial host-guest systems were prepared by intercalation of mono-deprotonated rosmarinic and salicylic acid (RA and SA), with recognized antibacterial and antioxidant properties, into a nitrate-intercalated MgAl layered double hydroxide (LDH) via anion exchange reaction. The structural, morphological, and thermal properties of the modified LDHs (i.e., MgAl-RA and MgAl-SA), compared with those of a fully exchanged ZnAl-SA, indicated the successful immobilization of the functional molecules. Linear low-density polyethylene (LDPE)/antibacterial-LDH nanocomposites were prepared by a two-step melt compounding procedure. X-ray diffraction analysis and scanning electron microscopy showed that MgAl-RA was better dispersed than ZnAl-SA and MgAl-SA. LDPE nanocomposites containing the highest filler content showed increased thermo-oxidation stability, with a marked effect for LDPE/MgAl-RA due to the antioxidant power of RA. Furthermore, the antibacterial activity of LDPE/MgAl-RA was high and selective toward Staphylococcus aureus. Finally, the overall migration of RA and SA from films of polymer nanocomposites immersed in ethanol solution was followed by fluorescence spectroscopy evidencing a controlled release of the active compounds.

Automated summary

Polymer nanocomposites with active and natural compounds dispersed in the polymer matrix offer a tunable way to develop antibacterial packaging materials. By intercalating mono-deprotonated rosmarinic and salicylic acid into nitrate-intercalated MgAl layered double hydroxide, antibacterial host-guest systems were successfully prepared, showing selective antibacterial activity against Staphylococcus aureus. The controlled release of active compounds from the polymer nanocomposites was evidenced by fluorescence spectroscopy, indicating the potential for practical application in food packaging.