Poly(lactic acid)-based bionanocomposites: effects of ZnO nanoparticles and essential oils on physicochemical properties

Abstract

The main shortcoming of polylactic acid (PLA) for packaging applications is its brittleness. Thus, there is a pronounced interest in the potential use of PLA/zinc oxide nanoparticle (ZnO NP) systems as active food packaging. In this study, ZnO NPs and two types of essential oils (EOs) including Zataria multiflora L. (ZEO) and Mentha piperita L. (MEO) at different concentrations (0.5%, 1%, 1.5% w/w) were used for the production of active PLA-based bionanocomposites for packaging applications. The presence of ZnO NPs and EOs led to increased film thickness and improved contact angle properties. ZnO NPs boosted the PLA-based films’ WVP, whereas the EOs had the opposite effect. The increase in the ZEO and MEO content reduced the ultimate tensile strength and Young’s modulus and increased the elongation at break. The X-ray diffraction and Fourier transform infrared spectroscopy results confirmed that the improvements are related to the ZnO NPs exfoliation and good interaction between PLA and ZnO NPs in the presence of EOs. Differential scanning calorimetry analysis showed that the incorporation of ZnO NPs increased the glass transition temperature (Tg), but did not change the melting temperature (Tm), though the addition of the EOs lowered the values of both parameters. Morphology analysis by scanning electron microscopy and atomic force microscopy showed that the presence of ZEO/MEO led to increased pinholes, pores, and roughness in the microstructure of the films. These results revealed that ZnO-PLA films containing EOs may be used as controlled release antimicrobial food active packaging.