Single microcapsules containing epoxy healing agent used for development in the fabrication of cost efficient self-healing epoxy coating

In this study, to reduce the size significantly, a number of microcapsules were prepared to apply in situ encapsulation method with poly(urea-formaldehyde) (PUF) as the shell material and epoxy resin (EPL 1012R) as the core substance. Upon that, a systematic investigation was done on the properties of microcapsules affected by the synthesis procedure. In their optimum state, the synthesis parameters were concluded to exhibit the following properties: viscosity of oil phase of 15-25 (mPa.s), initial pH = 4, emulsifier of sodium dodecyl benzene sulfonate (SDBS) and 0.5 (wt.%) content for the emulsifier. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA) were applied to study morphology, chemical structure, mean size, size distribution and thermal properties of the resulting microcapsules. The morphological study showed the microcapsules prepared by SDBS (0.5 wt.%) are of spherical nature with few adhesions and the average diameter 2.13 (μm) for encapsulation of epoxy resin. The yield and core content for those microcapsules were determined 50 (wt.%) and 54 (wt.%), respectively. Investigating the microcapsules' chemical structure revealed successful encapsulation of the epoxy resin in PUF shell and the results were confirmed by thermal analysis. Self-healing performance of the coatings containing epoxy-microcapsule was evaluated by salt fog corrosion test by ASTM B117 and eventually showed excellent corrosion resistance in scratched coatings confirming self-healing properties. Furthermore, electrochemical tests were employed for quantitative investigations of self-healing performance of the coating which confirmed the salt fog corrosion results.