Barrier functionality of SiO x layers and their effect on mechanical properties of SiO x /PLA composite films

Silicon oxide (SiOx) films are widely used as barrier layers in different types of commodity packaging and have caught the interest of manufacturers and researchers alike owing to their high barrier functionality, good acid and alkali resistance, ability to withstand high-temperature and microwave treatments, and good transparency. In this study, we first synthesized polylactic acid (PLA) films by extrusion calendaring and then deposited a SiOx layer on the PLA films by plasma-enhanced chemical vapor deposition to prepare SiOx/PLA composite films. We then evaluated the barrier functionality of the SiOx layer and elucidated its underlying mechanism. We also analyzed its effect on the mechanical properties of the composite films by comparing the oxygen and water vapor transmission rates, soil degradation performances, and surface morphologies of the two types of synthesized films (uncoated and coated with SiOx). The results showed that, because of the SiOx layer, the barrier properties and mechanical properties of the SiOx/PLA composite films were better than those of the uncoated films. In particular, the oxygen and water vapor transmission rates of the composite films were approximately 8–10 and 6–8 times lower, respectively, than those of the uncoated PLA films. In addition, the SiOx layer lowered the rate of soil degradation of the composite films, owing to which the weight-loss rates of the composite films were also lower than those of the uncoated films. Further, the tensile strengths and elongations at break of the composite films were higher because of the SiOx layer.Graphical Abstract