Surface-modified poly(methyl methacrylate) microcapsules containing linseed oil for application in self-healing epoxy-based coatings

Abstract

In this study, poly(methyl methacrylate) (PMMA) microcapsules filled with linseed oil (LO) as healing agent were prepared by solvent evaporation method. The effect of mechanical mixing rate in the range of 300–1000 rpm on mean size and morphology of PMMA microcapsules was investigated. Optical microscopy (OM) and scanning electron microscopy (SEM) images indicated that spherical microcapsules were formed with the mean size in the range of 2.6–11.6 μm. In order to enhance the interfacial interaction between microcapsule shell and epoxy matrix of coating, the surface of PMMA microcapsules was modified by hexamethylene diamine (HDMA). The chemical structure of amine functionalized-PMMA microcapsules was characterized by Fourier-transform infrared (FTIR). The surface modification results indicated that the roughness parameters (Rq and Ra) were higher for modified microcapsule compared to unmodified ones as proved by atomic force microscopy (AFM). Self-healing performance of epoxy coatings containing 10 wt. % (modified and unmodified) PMMA/LO microcapsules was evaluated in 3.5 wt.% NaCl aqueous solution using electrochemical impedance spectroscopy (EIS). The results indicated that the chemical surface modification of PMMA/LO microcapsules improves the healing performance of epoxy coatings as compared with the epoxy coatings filled with unmodified microcapsules. This can be due to the higher interfacial adhesion between the HMDA on the microcapsule surface and the epoxy matrix.