Superior mechanical performance of in-situ nanofibrillar HDPE/PTFE composites with highly oriented and compacted nanohybrid shish-kebab structure

Abstract

Hierarchical structures dominate the mechanical performance of polymer materials. In this work, in-situ nanofibrillar high-density polyethylene/polytetrafluoroethylene (HDPE/PTFE) composites with highly ordered and compacted nanohybrid shish-kebab (NHSK) structure were successfully fabricated using a self-made loop oscillating push-pull molding (LOPPM) equipment. Through the synergistic effect of the oscillatory push-pull shear flow field and PTFE, in-situ nanofibrillar HDPE/PTFE composites with superior strength and toughness were obtained. With the addition of 5 wt% PTFE in HDPE, the tensile strength, Young's modulus and impact strength of in-situ nanofibrillar composites reached 133.4 MPa, 4388.1 MPa and 69.1 kJ/m2, which was about 6.0, 6.0 and 3.1 times higher than that of neat HDPE, respectively. These superior improvements in mechanical performance were attributed to the oriented and compacted NHSK structure. Additionally, two-dimensional small-angle X-ray scattering (2D-SAXS), two-dimensional wide-angle X-ray scattering (2D-WAXS) and differential scanning calorimetry (DSC) results confirmed the synergistic enhancement effect of the flow field and PTFE on the degree of orientation, lamellar thickness, average length of shish and crystallization properties. Overall, it is believed that this proposed strategy can be extended to a wide range for the preparation of polymer materials with superior mechanical properties.