*2.3. Characterization*

The fracture surfaces of the PBAT/Ti3C2TX nanocomposite were characterized by scanning electron microscopy (SEM, Quanta 250, FEI, Hillsboro, OR, USA). The samples were fractured in liquid nitrogen for 30 min. They were observed at an accelerating voltage of 5 kV. Prior to the observation, all the samples were coated with a layer of gold.

Thermogravimetric analysis (TGA) of all PBAT/Ti3C2TX nanocomposites was conducted on a TG-209F1 thermal analyzer (Netzsch, Selb, Germany) to measure the thermal stability under air atmosphere. The samples of about 10 mg were heated from room temperature to 600 ◦C at a heating rate of 10 ◦C/min.

The crystallization and melting behaviors of PBAT/Ti3C2TX nanocomposites were conducted on a DSC-204F1 (Netzsch, Selb, Germany). The samples of approximately 5 mg were first heated to 180 ◦C at a heating rate of 10 ◦C/min to establish the thermal history, then cooled to 20 ◦C at a cooling rate of 10 ◦C/min and followed by a second heating

rate of 10 ◦C/min to 180 ◦C. The peak crystallization temperature (*T*cp), the peak melting temperature (*Tm*p), the crystallization enthalpy (Δ*H*c), and the melting enthalpy (Δ*H*m) of these samples were summarized. The degree of crystallinity of PBAT (*χ*c) was calculated by the following equation:

$$\chi\_{\varepsilon} = \frac{\Delta H\_m}{\Delta H\_0 (1 - q\_{\varepsilon})} \tag{1}$$

where Δ*H*<sup>0</sup> is the 100% melting enthalpy of PBAT (114 J/g) [36], and *ϕ*<sup>c</sup> presents the weight ratio of Ti3C2TX in the nanocomposites.

The tensile test was performed on an Instron 5566 universal electron tensile machine. The specimens were cut into rectangle shape with a dimension of 1 cm × 8 cm × 100 μm. The tensile speed was fixed at 10 mm/min. The reported results were the average values of at least five successful specimens.

The dynamical mechanical analysis was conducted on a Netzsch DMA 242E (Netzsch, Selb, Germany) analyzer. Tensile measurements were taken on specimens with dimensions of 30 mm at a fixed frequency of 1 Hz and from 90 ◦C to 70 ◦C at a ramping rate of 3 ◦C/min.

The 2D, wide-angle, X-ray scattering (2D-WAXS) measurements were carried out on an X-ray diffractometer (Rigaku UltimaIV, The Woodlands, TX, USA). The data were collected in the scanning range of 10–60◦ with a step of 0.02◦.

The oxygen transmission rate (OTR) of the oriented films was measured with a MO-CON OX-TRAN (Ametek Mocon, Brooklyn Park, MN, USA) 2/21 at 23 ◦C, 1 atm, and 85% RH. The water vapor transmission rate (WVTR) was determined according to ASTM E96-80 at MOCON PERMATRAN-W 3/33 (Ametek Mocon, Brooklyn Park, MN, USA). The reported values were the average results of three successful samples.
