**Scheme 1.** Schematic diagram of preparation of PBAT/Ti3C2TX nanocomposite biaxial stretching films.

The PBAT/Ti3C2TX nanocomposite biaxial stretching films were prepared by two steps. Prior to the experiment, the PBAT pellets were dried in a vacuum oven at 80 ◦C for 12 h. Firstly, the PBAT/Ti3C2TX nanocomposite casting film was prepared by extrusion casting (FDHU-35, Potpo, Guangzhou, China) so that the Ti3C2TX could have a better dispersion in the PBAT matrix. The temperatures from the hopper to the nozzle were set at 130-150-170-170-170-150 ◦C. The screw speed was set at 60 rpm. The thickness of the obtained PBAT/Ti3C2TX nanocomposite casting films was approximately 100 μm. The code of the samples was abbreviated as PBAT-X, where X represents the weight ratio of Ti3C2TX in the PBAT/Ti3C2TX nanocomposites.

The extruded PBAT nanocomposite casting films containing 1 wt% Ti3C2TX nanosheets were cut into squares (80 mm side length) for biaxial stretching. The biaxially oriented films were then prepared at different stretching ratios on a KARO 5.0 (Brückner MaschinenbauGmbH & Co., Siegsdorf, Germany) equipped with mechanically driven clamps. The stretched films were thermally annealed at a temperature of 110 ◦C for 60 s. Finally, the biaxially oriented nanocomposite films were obtained to characterize the crystal orientation and the gas barrier properties.
