Effect of root-like mechanical-interlocking interface in polypropylene/aramid fiber composites from experimental to numerical study

Poor interfacial interaction of fiber-reinforced polymer composites is a crucial impediment to expand the practical application. Here, we reported a facile strategy to construct a mechanically-interlocking interface in polypropylene (PP)/aramid fiber (AF) composite by utilizing the interfacial diffusion and epitaxial growth of amide-based self-assembling compounds (NA) on the surface of the reinforcing fiber driven by the polarity differences between the three components. The results showed that when NA was introduced to PP/AF composite, NA preferred to aggregate and immobilize on the AF surface by directed diffusion and self-assembly due to strong hydrogen bonding and similar polarity between AF and NA. Subsequently, the NA assembly epitaxially crystallized into branched fibers, forming root-like reinforcing fibers anchored on the interface and then inducing the formation of transcrystalline layers of PP. The branched fibers and transcrystalline layers imposed the mechanically-interlocking effect on the PP/AF interface to greatly enhance the interfacial interaction, with a remarkable increase of 48.1% in interfacial shear strength compared to the conventional PP/AF composite featuring smooth interface. To verify the mechanical enhancement effect, tentative impact and tensile tests were adopted and results presented that impact strength of PP/AF/NA composite with finely designed interfaces was improved by 22.0% in comparison with conventional PP/AF materials. Finally, the load-transferring mechanism from polymer to reinforcing fiber and the strengthening effect of the mechanical-interlocking interface were revealed by numerical study using the finite element method to pave the way of production of high-performance filler-reinforced composites.