*2.1. Materials*

The PLA (2003D; density and melting temperature were 1.24 g/cm<sup>3</sup> and 160 ◦C, respectively) was purchased from NatureWorks LLC (Minnetonka, MI, USA). The corn starch (St) was provided by Wuhan Huali Environmental Protection Technology Co., Ltd (Wuhan, Chian). The citric acid (CA) monohydrate and PEG 1000 (analytical purity) were purchased from Sinopharm Chemical Reagent Co., Ltd (Wuhan, Chian). The vegetable oil polyol (VOP) was provided by Dongguan Aoda Environmental New Materials Co., Ltd (Dongguan, Chian).

## *2.2. Preparation of the PLA*/*PSt*/*PEG*/*CA Sample*

PLA and starch were placed in a 60 ◦C vacuum drying oven and dried for 24 h to reduce the moisture content of the latter to approximately 3%. The PSt was prepared by mixing dry starch with VOP for 15 min at a mass ratio of 7:3. The mixtures of PLA, PSt, PEG, and CA were melt-blended at 170 ◦C with a rotation speed of 60 rpm for 10 min. A blend of different components was obtained, and the corresponding formulations are presented in Table 1. The mixtures were then pressed into plates with thicknesses of 1, 2, and 4 mm by using a plate vulcanizer. These plates were cut and polished into standard splines for testing. The samples were completely dissolved in dichloromethane, centrifuged three times, washed with ethanol to separate the precipitate, and then dried in a vacuum oven at 60 ◦C for 48 h.


**Table 1.** Material formulations.
