Increasing the physical and antimicrobial properties of polylactic acid by using additives

The aim of this study is to prepare low-cost new packaging materials with improved physical properties and strong antimicrobial properties that prevent the growth of microorganisms and extend the shelf life of food. In this study, new films with antibacterial properties were prepared by solvent casting method. Spruce resin, essential oil mixture, and silver nanoparticles (AgNP) were used to add antimicrobial properties to the polylactic acid (PLA) films. AgNPs were synthesized by polyphenol reduction provided from spruce resin dissolved in methylene chloride. The prepared films were subjected to physical tests. While spruce resin decreased the physical property of the films, other components increased most of the physical properties. Only spruce resin (SR) addition decreased the water vapor permeation (WVP) of the films, and only essential oils (EOs) addition increased this property due to their higher polarity. The physical properties of the prepared films, such as tensile stress (TS), elongation at break (EB), and elastic modulus (EM) were also measured. SEM, UV-Vis, FTIR, and thermal properties of the prepared films were also investigated. The antimicrobial properties of the prepared films were measured using Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria, and the agar disc well method was used to measure the antimicrobial properties. It has been observed that SR, AgNPs, EOs used in film preparation have antimicrobial properties. EOs, especially clove oil, have a positive effect on all properties of the prepared films except WVP. It has been concluded that additives can improve the physical properties of PLA to a certain extent.