**4. Conclusions**

In this study, the compatibilization between PLA and starch was improved through reactive blending, and the toughness of the PLA/PSt/PEG/CA blend was improved to a certain extent. The elongation at break of the blend with a PSt content of 30 wt% reached a maximum value of 140.51%, and the impact strength increased to 3.56 kJ/m2. The addition of a small amount of CA did not change the crystal form of starch, but CA participated in the esterification reaction during the blending process. The generated crosslinked/branched polyester adhered to the surface of the starch granules and improved the surface activity of starch and the compatibility between starch and PLA. The particle size and shape of the starch in the blend did not significantly change, which indicated that the esterification reaction only occurred in the amorphous region of starch. The decrease in the hydrophilicity and the increase in the tensile toughness of the PLA/PSt/PEG/CA blend compared with that of PLA/PSt/CA suggested that PEG may also participate in the esterification reaction during melt blending.

The findings sugges<sup>t</sup> that PEG, which acts as a plasticizer for PLA and starch, can lubricate the system. Moreover, when PEG is dispersed in the PLA and starch, the branched/crosslinked polyester containing PEG chains, which is formed by the esterification reaction, is easily embedded in the interface between PLA and starch. This polyester enhances the interaction between PLA and starch. These results indicate that PEG can form a highly stable crosslinked/branched polyester on the starch surface after participating in the esterification reaction to further improve the compatibility between PLA and starch. Furthermore, the decrease in the water absorption can help enhance the stability of the blend material in a natural environment.

**Author Contributions:** Conceptualization, H.H. and X.Z.; Data curation, H.H.; Investigation, A.X. and D.Z.; Project administration, S.P.; Resources, W.Z.; Writing—original draft, H.H.; Writing—review & editing, H.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** The work is funded by National Natural Science Foundation of China (51273060), the Open Fund of Hubei Provincial Key Laboratory of Green Materials for Light Industry.

**Acknowledgments:** The work is funded by National Natural Science Foundation of China (51273060), the Open Fund of Hubei Provincial Key Laboratory of Green Materials for Light Industry.

**Conflicts of Interest:** The authors declare no conflict of interest.
