Layer-by-Layer Self-Assembly Strategy for Surface Modification of Aramid Fibers to Enhance Interfacial Adhesion to Epoxy Resin

: In this work, the layer-by-layer self-assembly technology was used to modify aramid fibers (AFs) to improve the interfacial adhesion to epoxy matrix. By virtue of the facile layer-by-layer self-assembly technique, poly(l-3,4-Dihydroxyphenylalanine) (l-PDOPA) was successfully coated on the surface of AFs, leading to the formation of AFs with controllable layers (nL-AF). Then, a hydroxyl functionalized silane coupling agent (KH550) was grafted on the surface of l-PDOPA coated AFs. The properties such as microstructure and surface morphology of AFs before and after modification were characterized by FTIR, XPS and FE-SEM. The results confirmed that l-PDOPA and KH550 were successfully introduced into the surface of AFs by electrostatic adsorption. The interfacial properties of AFs reinforced epoxy resin composites before and after coating were characterized by interfacial shear strength (IFSS), interlaminar shear strength (ILSS) and FE-SEM, and the results show that the interfacial adhesion properties of the modified fiber/epoxy resin composites were greatly improved.