"Poly(lactic acid) (PLA) films were coated with chitosan and chitosan-graphene (chitGRH) layers. To prepare the coating layers, first, graphite was added directly into chitosan acid solution. After 30 min of ultrasonication, graphene layers in graphite were dispersed evenly in the solution due to the similar surface energies between chitosan and graphene. Chitosan acid solution was also ultrasonicated for 30 min. Before coating, PLA films were treated with oxygen plasma at 300 Watt for 10 min on both sides to enable evenly coating of chitosan solution distribution on PLA's surface. Then, a roll coating machine was used to apply 3 or 10 layers of chitosan or chitGRH solution on each side of the PLA films. Thicknesses of the coating layers were determined by a scanning electron microscope. Thermal gravimetric analysis and differential scanning calorimetry studies showed that the coating layers did not affect PLA's bulk properties (i.e., glass transition and melting temperatures, and crystallinity). Oxygen permeability (OP) tests were conducted at 23 °C and 0, 30, 60, and 90% relative humidity (RH). Oxygen plasma treatment did not affect the OP of the coated PLA films. The addition of both chitosan and chitGRH layers reduced the OP of PLA films by three order of magnitude at 0% RH. The effectiveness of chitosan on reducing the OP of the multilayer structure depended on the test RH due to chitosan hydrophilicity. ChitGRH was more effective to reduce OP at 60% RH. The development of PLA- chitGRH multilayer films open the possibility of producing compostable high oxygen barrier multilayer films."--Page ii.
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