Cellulose acetate/AgNPs-organoclay and/or thymol nano-biocomposite films with combined antimicrobial/antioxidant properties for active food packaging use

Abstract

Nano-biocomposite films based on plasticized cellulose acetate/triethyl citrate (CA/TEC) were prepared with silver nanoparticles (AgNPs)/gelatin-modified montmorillonite nanofiller (AgM) and thymol (Th). AgNPs were biosynthesized in situ the clay using Curcuma longa (C. longa) tuber extract. Full characterization of clay and the formulated films was conducted including morphological, physical and functional properties. From the results, the AgNPs showed spherical shape, face centred cubic crystalline structure, and small average size with narrow distribution. Intercalated structure of films was achieved with some exfoliated platelets and clay aggregates. The glass transition temperature (Tg) of CA increased slightly by the added clay but decreased by Th due to its plasticizing effect. Also, the thermal stability of CA was enhanced only by the added clay. Increasing contents of both additives into films declined the optical clarity but enhanced greatly the UV barrier ability. The clay improved the tensile and oxygen barrier properties, while the Th initiated an antagonist effect. Besides, the radical 2,2‑diphenyl‑1‑picrylhydrazyl (DPPH) tests highlighted antioxidant activities of Th-included films. The films showed antimicrobial activities against bacteria and fungi, where Escherichia coli (E. coli) was the most sensitive, with an efficient growth inhibition in vapour-phase method. These materials with antimicrobial/antioxidant properties are promising active packaging.

Keywords: Active food packaging; Antimicrobial and antioxidant activities; Cellulose acetate; Curcuma longa extract; Montmorillonite; Silver nanoparticles; Thymol.