Simultaneous enhancement of strength and toughness of polybutylene terephthalate composites via oriented shish-kebab crystals induced by oriented polytetrafluoroethylene nanofibres

Balancing strength and toughness remains a significant challenge in composite materials research. Here, we quantitatively analysed the effect of the content of oriented fibres and the crystal orientation degree on the mechanical properties of a composite to overcome this limitation. Polytetrafluoroethylene (PTFE) was fibrillated in situ and then oriented by the shear flow field within a Polybutylene terephthalate (PBT) matrix. The impact of the oriented PTFE fibres on the rheological properties, crystallisation behaviour, crystal morphology and mechanical performance of PBT was systematically examined. The introduction of PTFE nanofibres into the PBT matrix promoted the development of oriented shish-kebab structures in the composite and enhanced the crystallinity of PBT. When the oriented PTFE nanofibre content was less than 1.5 phr, it was positively correlated with the crystal orientation degree of PBT. The oriented shish-kebab structures formed by the addition of 1.5 phr oriented PTFE nanofibres (sample PBT (PTFE1.5)) yielded the optimal improvement in mechanical properties. Compared with the tensile and impact strengths of pure PBT (spherulite structure), those of PBT (PTFE1.5) increased by 37.15 % and 180.94 %, respectively. This research offers an innovative, feasible strategy enabling polymers to enhance the strength and toughness of PBT composites simultaneously, with potential applications in high-performance domains, such as automotive and precision instrumentation.