Synchronous Toughening, Strengthening, and Ultraviolet Resistance of Immiscible Polylactic Acid/polypropylene Carbonate Blends Compatibilized by a Low Threshold of Reactive Janus Nanosheets

Poor toughness limits the use of biobased and biodegradable polylactic acid (PLA). The conventional method of blending with flexible polymers toughens PLA with a significant loss of strength and incompatibility. In this work, carbon dioxide-based biodegradable polypropylene carbonate (PPC) was used as the flexibilizer, and PPC-TiO2-epoxy Janus nanosheets (JNs) synthesized by grafting PPC-diols and epoxy groups onto each side of titanium dioxide nanosheets respectively were used as compatibilizers. PLA/PPC/JNs blends were then prepared by melt processing. The in situ reaction between the epoxy groups on one side of the JNs and the carboxylic acid groups on the PLA occurs, forming a solid covalent bond. The grafted PPC chains on the other side of the JNs were tightly entangled with those of the PPC flexibilizer. Moreover, due to the Pickering effect of JNs, they can stably anchor at the interface, which reduces the interfacial tension and significantly enhances compatibility. Compared with PLA/PPC, the addition of as low as even 0.3 wt % JNs reduced the PPC domain size from 3.25 to 0.42 mu m, and consequently, the elongation at break increased by 250%. Moreover, the introduction of JNs significantly improved the UV shielding in both UV-A and UV-B regions and the UV aging resistance of the blends without reducing the transparency that much. Herein, this work provides a new method for improving the compatibility of PLA-based blends and preparing high-performance PLA materials.