Direct Formation of Nanohybrid Shish-Kebab in the Injection Molded Bar of Polyethylene/Multiwalled Carbon Nanotubes Composite

Abstract

The formation of a nanohybrid shish-kebab (NHSK) superstructure, in which fibrillous carbon nanotubes (CNTs) act as shish while polymer lamellae act as kebab, is a novel way to bond the polymer and CNTs together and was first observed in the solution crystallization of polyethylene in the presence of CNTs. In this work, a direct formation of nanohybrid shish-kebab in the injection molded bar of high-density polyethylene (HDPE)/multiwalled carbon nanotubes (MWCNTs) composite, has been achieved, via a so-called dynamic packing injection molding technology (DPIM), in which oscillatory shear field was imposed on the gradually cooled melt during the packing solidification stage. Interestingly, whatever the long axis of CNTs is perpendicular to or parallel to the shear flow direction, the lamellae of PE is always perpendicular to long axis of CNTs. The three-step mechanism, including (1) the disentanglement and orientation of both PE and CNTs, (2) PE folded-chain lamellae directly nucleated on CNTs surface and/or first formation of PE extended-chain shish directly on CNTs surface then followed by nucleation of folded-chain lamellae, and (3) the crystallization of PE kebabs on the PE decorated CNTs fibrils, was proposed to understand the formation of NHSK under effect of shear. Importantly, the NHSK structure can bring significant mechanical reinforcement in the HDPE/MWCNTs composite. For the oriented composites containing 5% MWCNTs, its tensile strength is increased by 150% and 270%, compared to the oriented pure HDPE and the isotropic composites containing 5% CNTs, respectively; meanwhile, its Young’s modulus is enhanced by 130% and 180%, compared to the oriented pure HDPE and the isotropic composites containing 5% CNTs, respectively. This work is the first to enlarge the theoretical value and application potential of NHSK structure in the crystallizable polymer/CNTs composite.