*2.3. Characterization*

## 2.3.1. Mechanical Property Measurements

The hot pressed 2 mm-thick plate-shaped samples were cut and polished into dumbbell-shaped samples in accordance with the international standard ISO 527-2. The CMT-4204 electric tensile tester (SANS, Shenzhen, Chian) was used to test the samples at a tensile speed of 5 mm/min to obtain the stress–strain curve, tensile strength, and elongation at break. The 4 mm-thick samples were cut into a standard spline in accordance with ISO 179-1, and the impact energy was measured through the

Charpy impact test (SJJ-50, Chengde, Chian) with a range of 0.5 J. The impact strength of the sample was obtained using data calculation. The data of the samples in every test were measured on at least five splines.

## 2.3.2. Rheological Behavior Analysis

A rotating plate rheometer (AR2000EX, TA, Shanghai, Chian) was used to obtain the linear rheological behavior of the mixture with plate–plate geometry. The sample is a 1 mm-thick disc with a diameter of 25 mm. The set temperature was 170 ◦C, the frequency range was 0.1–100 Hz, and the strain was 0.1%.

## 2.3.3. Di fferential Scanning Calorimeter (DSC)

A DSC (Perkin Elmer, DSC 8000, Kunming, Chian) was used for crystallization performance analysis of the PLA/PSt/PEG/CA blend. The sample was heated from 30 to 200 ◦C at a rate of 10 ◦C/min and maintained at 200 ◦C for 3 min to eliminate the previous thermal history and then cooled to 30 ◦C at a rate of 10 ◦C/min. The sample was heated again from 30 to 200 ◦C at the same increase rate. The second heating curve was recorded, and the crystallinity of PLA was calculated as [16]

$$X\_{\rm c} = \frac{\Delta H\_m - \Delta H\_{\rm c}}{\Delta H\_f \omega\_{\rm PLA}} \times 100\% \tag{1}$$

where *Xc* represents the crystallinity of PLA, Δ *Hm* and Δ *Hc* are the melting enthalpy and cold crystallization enthalpies of the sample, respectively, and Δ *Hf* and ω*PLA* are the melting enthalpy and PLA mass fraction of 100% crystallized PLA, respectively.

## 2.3.4. Scanning Electron Microscopy (SEM)

The morphology of the impact fracture surface was examined using a SEM (JSM-6390L V, JEOR, Tokyo, Japan) at an acceleration voltage of 10 kV. The 4 mm-thick sample was broken at room temperature, and the impact fracture surface was washed with ethanol.

## 2.3.5. X-Ray Di ffraction (XRD)

The XRD analyzer from Panalytical B.V. (Empyream, Almelo, NL, USA) was used to test the pretreated powder samples with the target of Cu, test conditions: voltage = 40 kV, current = 30 mA, start angle = 5◦, end angle = 40◦, and scan step width = 0.02◦.

## 2.3.6. Fourier-Transform Infrared (FTIR) Spectroscopy

The blend was dissolved in dichloromethane (CH2Cl2), washed with ethanol, and dried to obtain powder samples. The powders were mixed with potassium bromide at a weight ratio of 1:100 and subsequently compressed. Measurements were performed using an FTIR spectrometer (Iso10, Nicolet, Beijing, Chian) with a resolution of 4 cm<sup>−</sup><sup>1</sup> and scan number of 32.
