Development of biobased multilayer films with improved compatibility between polylactic acid-chitosan as a function of transition coating of SiOx.

A SiOx coating prepared via plasma-enhanced chemical vapor deposition (PECVD) technique was used as a transition layer between polylactic acid (PLA) and chitosan (CS) to form a three-layer composite film of PLA/SiOx/CS. The effect of oxygen plasma irradiation time (0 s, 30s and 60s) on SiOx surface and PLA-CS interface was examined based on the contact angle, pull-off test and scanning electron microscope (SEM). The mechanical, barrier and antibacterial properties of PLA/SiOx/CS films were also investigated. The results showed that oxygen plasma irradiation improved the hydrophilicity of the SiOx surface and the adhesive strength between SiOx-CS of PLA/SiOx/CS films in a time-dependent manner. SEM examination revealed a gap between PLA/CS layers, but the interfacial separation among layers in PLA/SiOx/CS films disappeared as the transition layer of SiOx and oxygen plasma irradiation (60s) intensified. Notably, the oxygen barrier property and antibacterial activity of PLA/SiOx/CS films were dramatically enhanced. Additionally, moisture resistance was slightly decreased following the incorporation of the CS coating compared with the PLA film. The tensile strength of the composite film also increased with the number of layers, while elongation at break decreased. The prepared PLA/SiOx/CS films with multifunction are promising applied in food packaging as biobased materials.