Interfacially located nanoparticles: Barren nanorods versus polymer grafted nanorods

Polymer blend nanocomposites with the nanoparticles exclusively located at the interface have attracted significant attention while the compatibilization functions of such nanoparticles in the blends are still controversial. Herein, the pristine boehmite nanorods (p-BNRs) and epoxide group modified boehmite nanorods (m-BNRs) have been synthesized and incorporated in the immiscible Poly(L-lactide)/Poly(1,4-butylene succinate) (PLLA/PBSU) blends. It is found that both p-BNRs and m-BNRs are thermodynamically located at the interface and the phase morphologies of the two nanocomposites are very similar at the same nanofiller loadings. However, the two nanocomposites exhibit different mechanical properties. The PLLA/PBSU blend nanocomposites with m-BNRs show increased elongation at break, enhanced notched impact strength and improved yield strength, as compared with the binary PLLA/PBSU blends. In contrast, p-BNRs lead to drastically deteriorating mechanical properties of the PLLA/PBSU blends even with all p-BNRs located at the interface. The investigation indicates that p-BNRs at the interface have barren surface and are lack of specific interactions with the polymers in the neighboring phases. In contrast, the epoxide groups on m-BNRs reacted with the end carboxylic acid groups of both PLLA and PBSU and the polymer chains were chemically bonded onto the surface of nanorods. The chemically bonded polymer chains on the nanorods at the interface can entangle with the molecular chains of the two polymers to enhance the interfacial adhesion. This paper demonstrates the significance of molecular chain entanglements of the compatibilizing nanoparticles and paves a new possibility to fabricate new materials with simultaneously enhanced strength and toughness.