Self-sterilized EVOH-TiO2 nanocomposites:: Interface effects on biocidal properties

Nanocomposite materials obtained by TiO2 incorporation into ethylene-vinyl alcohol copolymers, extensively used in food packaging, are prepared via a straightforward melting process. The structural characteristics of the nanocomposites are examined using wide and small angle X-ray scattering (WAXS/SAXS), and vibrational infrared and Raman spectroscopies. A microscopy (SEM/TEM) study shows that the materials obtained are highly homogeneous at the nanometric scale, exhibiting an intimate contact between both the organic and inorganic components. TiO2 incorporation into this polymer matrix renders self-sterilized nanocomposite materials upon light excitation, which are tested against nine micro-organisms (gram-positive and gram-negative bacteria, cocci, and yeasts) typically involved in food contamination and/or degradation. Overall, the nanocomposites display an impressive performance in the killing of all micro-organisms with a maximum for an oxide content between 2-5 wt %. The measurement of the physico-chemical properties together with the structural characterization of the materials provide conclusive evidence that the nanocomposites biocidal capability born of the nanometric organo-morganic interface and rationalize the existence of a maximum as a function of the TiO2 content.