Enhanced interfacial strength of aramid fiber reinforced composites through adsorbed aramid nanofiber coatings

Aramid fibers are well-known for their excellent tensile properties and low density but are limited in composite applications due to their inert surface which leads to poor interfacial properties. One method that has shown promise in recent years is the application of nanoscale reinforcements to the surface of the fibers to improve mechanical interaction with the matrix. With aramid fibers, it is ideal to perform an interfacial reinforcement utilizing the dense hydrogen bonding which is responsible for the fibers strength. Here, it is demonstrated that recently developed aramid nanofibers (ANFs) can adsorb onto the surface of macroscale aramid fibers to enhance the interfacial properties through mechanical interlocking with the matrix. A simple and rapid dip-coating process is used to deposit the ANFs on the aramid fiber surface. These ANFs bond with the fiber through physisorption and hydrogen bonding, yielding a 70.27% increase in interfacial shear strength and a 25.6% increase in short beam shear strength in composites prepared by dip-coating unidirectional tape into a solution of ANFs. Notably, the interfacial gains are made while fully preserving the strength of the aramid fiber following the treatment, therefore ensuring in-plane properties of the composite are maintained. This work shows that the introduction of an ANF interphase may present a novel and convenient method to improve the interfacial strength of aramid reinforced composites, enabling cost-effective and simplified production of stronger structural materials.