Bionanocomposite films developed from corn starch and natural and modified nano-clays with or without added blueberry extract

Edible and bionanocomposite films were developed by extrusion followed by thermo molding. Corn starch (Zea mays), glycerol, and several nano-clays were used as the carbohydrate polymer, plasticizer and nano-fillers, respectively. Pure blueberry (Vaccinium corymbosum) extract (BE, 100% anthocyanin), as well as natural and modified montmorillonites (Mnt) with or without BE nano-packaged within their layers were incorporated into the thermoplastic starch (TPS) matrix. Previous studies by our research group have shown that BE, and BE nano-packaged within natural and modified Mnt, are pH-sensitive. With this in mind, we set out to develop edible and intelligent (pH-sensitive) bionanocomposite films with improved properties. Unfortunately however, none of the films formulated were pH-sensitive. All the films showed X-ray diffractograms typical of semicrystalline, albeit largely amorphous, materials coinciding with the morphological observations made under scanning electron microscopy. The results confirmed that total starch gelatinization occurred under the selected extrusion conditions. Films prepared from corn starch containing BE showed a plasticizing effect, giving materials with lower thermal resistance and surface moisture values, which were also more opaque, denser, and rougher. All the nano-fillers tested were completely exfoliated within the TPS matrix, except for the natural Mnt that was partly exfoliated and partly intercalated in the matrix. In general, materials containing nano-fillers with a greater degree of interlayer spacing (more exfoliated) showed higher thermal resistance and Young's modulus, but lower strain at break values.