Synthesis of robust polyaniline microcapsules via UV-initiated emulsion polymerization for self-healing and anti-corrosion coating

A novel kind of robust PANI microcapsules were prepared via a one-pot photopolymerization and interfacial aniline polymerization. In our strategy, lignosulfonate was employed as emulsifier to stabilize oil-in-water emulsion, in which the oil phase was composed of self-healing agent (tung oil), photo-crosslinkable acrylic monomer and crosslinker. Under UV light, the acrylic monomer and crosslinker were photo-polymerized and formed a cross-linked polyacrylic shell, endowing sufficient robustness to the microcapsules. Aniline was subsequently added to the water phase and polymerized at the oil-water interface, which converted to a second shell and endowed anticorrosion property. FTIR, TGA and SEM tests proved the successful preparation of PANI microcapsules, and the loading of tung oil in the microcapsules reached 55.1 wt%. These microcapsules could keep integrity and be uniformly dispersed in water-based epoxy coating. The incorporation of PANI microcapsules in the coating not only imparted self-healing properties to the coatings, but also greatly enhanced its anticorrosion performance. The scratch test indicated that the coatings containing only 5 wt% microcapsules could autonomously heal a scratch with 50 μm in width. In addition, the healed coatings with the microcapsules showed almost no corrosion products after 500 h salt spray test (SST), while for the scratched neat epoxy coating, a large area of coating peeled from the substrate after only 200 h SST. The remarkably enhanced corrosion protection capability was owing to the closure of the scratch by the self-healing effect and the inhibition efficiency of PANI.