6 - Biodegradable food packaging nanocomposites based on ZnO-reinforced polyhydroxyalkanoates

Abstract

Polyhydroxyalkanoates (PHAs) are a family of water insoluble, biodegradable, and biocompatible polyesters produced as reserve materials by a large number of bacteria under nutrient growth limiting conditions that have lately gained a lot of interest as food packaging materials. Among them, poly(3-hydroxybutyrate) (PHB) and its copolymer with valerate (PHBV) are the most representative because of good permselectivity, thermal, and mechanical properties. However, they suffer from low barrier to gases and water vapor, lack of transparency, brittleness, low melt stability, and narrow processing window. To overwhelm these shortcomings with the intention to extend their applications, novel strategies are required, such as, filling with nanofillers. In this regard, PHB- and PHBV-based bionanocomposites incorporating different amounts of zinc oxide (ZnO) nanoparticles were synthesized using a solution casting method, and their morphology, thermal, mechanical, barrier, migration, and antibacterial properties were analyzed. The nanoparticles increased the crystallinity, thermal stability, Young’s modulus, tensile and impact strength of the biopolymers, and enhanced the vapor barrier properties. Further, they provided antibacterial activity against Gram-positive and Gram-negative bacteria. In nonpolar and polar simulants, the migration levels of the composites were considerably below the limits of existing legislation for food packaging materials. These bionanocomposites are an interesting alternative to petroleum-based plastics for the storage of food and beverages.