Mechanical Properties And Impact Fracture Behavior Of Long-Polyimide-Fiber-Reinforced Poly(Butylene Terephthalate) Composites

The present study has been focused on the mechanical properties, impact behaviors and morphology of a new long-fiber-reinforced composite system based on poly(butylene terephthalate) (PBT) and (PI) polyimide fiber. A series of PBT composites with different weight fractions of PI fiber were prepared through melt pultrusion. The mechanical characterization revealed that the obtained composites achieved significant improvements not only in tensile and flexural strength but also in impact toughness. It is highlight that the Izod impact strength was improved by a factor of five when 12 wt% PI fiber was incorporated into the matrix. The scanning electronic micrograph observation indicated that the fiber pullout is the dominant mechanism for tensile failure, whereas the enhancement of impact toughness is attributed to the energy dissipation by both the fiber pullout and fiber strain. In this case, a simple fiber strain energy model can be used to predict the impact strength of this composite system. The theoretical results show a good fit with the experimental data of impact energy, implicating that the fiber strain energy absorption is involved in the major dissipation of impact energy when the fibers are debonded out of the matrix. In addition, the incorporation of PI fiber cannot only enhance the crystallinity of PBT due to the heterogeneous nucleating effect but also improves the thermal stability of composites by promoting the carbonization of the matrix. As a result of this study, the high performance composites based on a thermoplastic matrix and an organic reinforcing fiber were created for engineering and structural applications.