Poly(Lactic Acid)/ZnO Bionanocomposite Films with Positively Charged ZnO as Potential Antimicrobial Food Packaging Materials

Abstract

A series of PLA/ZnO bionanocomposite films were prepared by introducing positively surface charged zinc oxide nanoparticles (ZnO NPs) into biodegradable poly(lactic acid) (PLA) by the solvent casting method, and their physical properties and antibacterial activities were evaluated. The physical properties and antibacterial efficiencies of the bionanocomposite films were strongly dependent on the ZnO NPs content. The bionanocomposite films with over 3% ZnO NPs exhibited a rough surface, poor dispersion, hard agglomerates, and voids, leading to a reduction in the crystallinity and morphological defects. With the increasing ZnO NPs content, the thermal stability and barrier properties of the PLA/ZnO bionanocomposite films were decreased while their hydrophobicity increased. The bionanocomposite films showed appreciable antimicrobial activity against Staphylococcus aureus and Escherichia coli. Especially, the films with over 3% of ZnO NPs exhibited a complete growth inhibition of E. coli. The strong interactions between the positively charged surface ZnO NPs and negatively charged surface of the bacterial membrane led to the production of reactive oxygen species (ROS) and eventually bacterial cell death. Consequently, these PLA/ZnO bionanocomposite films can potentially be used as a food packaging material with excellent UV protective and antibacterial properties.

Dielectric, Thermal and Mechanical Properties of l,d-Poly(Lactic Acid) Modified by 4′-Pentyl-4-Biphenylcarbonitrile and Single Walled Carbon Nanotube

“…However, among disadvantages of l , d -PLA the most important ones are low glass transition temperature, low thermal stability, high brittleness and low crystallization rate. Binary and ternary mixtures or blends were created to improved selected properties of l , d -PLA and examples of some components are listed:a low molecular weight plasticizer, for example, acetyl tributyl citrate [30,31];polymers such as: poly(butylene adipate-co-terephthalate) [32,33] poly(butylene succinate) [34,35], poly(hydroxy butyrate) [36,37], polyaniline with multiwalled carbon nanotubes as flexible free-standing electrode for supercapacitors [38];carbon nanotubes [39,40,41,42,43,44,45];graphene and graphene oxide [46,47,48];liquid crystalline poly [4,4′-bis(6-hydroxyhexyloxy) biphenyl phenylsuccinate] as functional chain to copolymerize with PLA, towards improve the flexibility of PLA and caused interactions with multiwalled carbon nanotubes via π–π interaction [49];magnesium as filament based 3D printing [50];TiO 2 for antibacterial packaging [51];ZnO as potential antimicrobial food packaging materials [52];high-density polyethylene/carbon black composites as electrically conductive composites with a low percolation threshold [53]. …”

Recent Advances in Zinc Oxide Nanostructures with Antimicrobial Activities

“…In a previous article, we have reviewed the cytotoxic effects of ZnO nanostructures on mammalian cells [67]. As mentioned, ZnO NPs are widely used in cosmetics, suncreams, UV-absorbing packaging films and fabrics for food and medical textile applications, as well as therapeutic agents for cancer treatment [42][43][44][45][46]67]. In addition, ZnO NPs have also been added to animal (e.g., chicken) feed to promote the growth performance of the animals [319].…”

https://researchopenworld.com/current-trends-in-the-field-of-bioplastics-and-nanotechnology-polylactide-zno-nanocomposites-designed-with-multifunctional-properties/#

“…ZnO is well-known environmentally friendly and multifunctional inorganic filler characterized by effective antibacterial function and intensive ultraviolet absorption [11,12]. Until now, ZnO as well as other zinc-related compounds have been successfully utilized as effective catalysts for lactide polymerization and in "unzipping" depolymerization of PLA that allows its chemical recycling.…”