Surface modification of self-healing poly(urea-formaldehyde) microcapsules using silane-coupling agent

Poly(urea-formaldehyde) (PUF) microcapsules, which are used as self-healing component of fibre reinforced resin matrix composites, were prepared by in situ polymerization method. The surface of PUF microcapsules was modified by using 3-aminopropyltriethoxy silane-coupling agent (KH550), and the interfacial interactions between PUF microcapsules and KH550 was also studied. Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectra (XPS) analyses showed that the silane-coupling agent molecular binds strongly to PUF microcapsules surface. Chemical bond (Si–O–C) was formed by the reaction between Si–OH and the hydroxyl group of PUF microcapsules, also there have chemical adsorption effect in the interface simultaneously because of the existence of hydrogen bond between Si–OH and the hydroxyl group of PUF microcapsules. Scanning electronic microscopy (SEM) observation showed that a thin layer was formed on the surface of modified PUF microcapsules. Additionally, fractured surface were observed under SEM to investigate the interfacial adhesion effect between PUF microcapsules and epoxy matrix. The result indicted that the silane-coupling agent play an important role in improving the interfacial performance between microcapsules and resin matrix.