Fabrication of super-toughened polypropylene-based nanocomposite with low elastomer content through tailoring the microscale damage mechanisms

Structural composites with high fracture toughness have wide applications in various fields. However, achieving high toughening efficiency at low fabricating cost is still challenging. Here, one-dimensional carbon nanofibers (CNFs) were incorporated into the ethylene-octene copolymer (POE)-toughened polypropylene (PP) blends. The fracture behaviors of the samples were systematically researched under different load conditions, such as impact load condition, three-point bending test and single-edge notched tensile (SENT) measurement, and then the toughening mechanisms were proposed. The results indicated that CNFs dramatically enhanced the fracture toughness of the PP/POE blends due to that CNFs prevented the initiation and propagation of crazes. Furthermore, through incorporating an additional annealing treatment, the fracture mechanism of composites changed from crazing fracture to shear yielding-crazing fracture, which endowed CNFs with more apparent toughening effect. For example, at POE and CNF contents of 25 wt% and 1 wt%, the annealed composite sample showed the impact strength of 69.4 kJ/m(2) and elongation at break of 395.3%, which were increased by 208.4% and 92.0% compared with the unannealed binary blend, respectively. This work gives a novel insight to understand the toughening effect of one-dimensional nanofillers in the plastics/elastomer blends, and the methods may be used to toughen the other blend composites.