Preparation And Properties Of Moisture Curing Type Self-healing Microcapsules

In recent years, self-healing materials, including coatings, become more attractive due to its self-healing capabilities. It can significantly cut down the expenses of maintenance and repairing. However, the researches of self-healing coatings mainly focused on the preparation processes of microcapsules, selection of microcapsules’ core and shell material. While the instability of core material, and mechanical properties of single microcapsule are still need to be resolved before the practical application. In this work, moisture curing type double layed self-healing microcapsules were conveninently prepared with higher core material stability, and adjustable mechanical properties of shell. And self-healing anticorrosion coating was prepared with embeding these microcapsules in epoxy resin. Self-healing property of the coating and mechanical properties of the microcapsules was investigated, the results expanding and deepen the theory of the mechanical properties in microscopic-macroscopic scale.In this paper, moisture curing type double layed self-healing microcapsules were prepared by interfacial and in situ polymerization technology with polyurea(PU) and melamine-formaldehyde(MF) as shell material and isophorone diisocyanate(IPDI) as core materials. The chemical structure, morphology, particle size distribution and thermal stability of the microcapsules were studied with Fourier transform infrared spectroscopy(FTIR) and X-ray photoelectron spectroscopy(XPS), optical microscopy(OM), scanning electron microscopy(OM), transmission electron microscopy(TEM), mastersizer 3000 and thermal gravimetric analysis(TGA) respectively. And, core fraction of the microcapsules was measured with Soxhlet extraction. The influence of the preparing conditions such as aging time, ice bath, prepolymer of melamine(P-MF), amine chain extender and emulsification agitation rate were investigated to uncover the principle of core fraction and morphology of microcapsules, and the optimum preparing conditions were summaried. The results showed that PU/MF double layed microcapsules containing IPDI core were successfully prepared with regular spherical shape, the microcapsule shell was divided into a smooth outer layer and a rough inner layer,and the two layers may not have explicit boundary. The microcapsule prepared under the condition of ice-bath, adding P-MF and polyetheramine(PEA) D230, 1500 rpm agitation rate and 2h aging time were of better size distribution, thermal property and the best core fraction and morphology.At the same time, the mechanical properties of a single microcapsule prepared with optimum conditions were characterized by micromanipulation system.Several operations, such as compression-holding and compression-release, were conducted on the microcapsule with a probe. The effects of aging time and chain extender on the mechanical properties of microcapsules were researched by compressing microcapsules to rupture. The Young’s modulus of the microcapsules was calculated by mathematical model fitting, and the preparaion conditions can be optimized with this strategy. Moisture curing type self-healing coatings were prepared by dispersing microcapsules obtained at optimum conditions in an epoxy resin substrate. Moisture curing self-healing mechanism of this system was discussed and the influence of excess amine curing agents on the moisture curing rate was investigated. Moreover, the self-healing effect of the coating was preliminary characterized. The results showed that the microcapsule showed plastic behavior under small deformation(≤8.66%) while visco-plastic behavior under big deformation( ≥ 12.67%). The parameters of the microcapsules’ mechanical properties can be regulated by controlling the particle size, shell wall thickness and molecular structure of the microcapsules. It can meet the requests of different resin substrate. Synergistic effect on the moisture curing reaction can be formed with remaining amine curing agent in the self-healing epoxy coatings. The cracks on the coatings can be completed from healing after immersion in wet conditions for 48 h.