Research On Synthesis And Application Of Epoxy Resin Microcapsules As Self-healing Materials

At present, anticorrosion coatings cannot really realize the function of multiple self healing cycles. This project of this paper is to design a new self-healing anticorrosion coating by controlling the interface energy of components in the system and the structure and surface energy of active cells. The microcapsules were given the property of migrating to surface which was similar to that of fluorine and silicon. At the same time, the responses of the distribution combined with structure and properties of microcapsules to the stress of crack were simulated and optimized. The results of this research will be used to guide the design of self-healing coating.Poly(urea-formaldehyde) microcapsules was prepared using urea formaldehyde resin as shell material and epoxy resin(E-51) as core material by interfacial polymerization, sonication technique and in situ polymerization. Effects of different preparation methods on properties of microcapsules for self-healing materials were investigated. Optical microscope(OM), scanning electron microscope(SEM) and Fourier transform infrared spectroscopy(FTIR) results the microcapsules the best preparation method for the in situ polymerization. When the core/shell mass ratio was 2:1, mass concentration of gum arabic(used as emulsifier) was 0.8 % and stirring speed was 400 r/min, the w(core) was 79.8 %, the mean diameter was 820 nm, showed good sphericity,narrow diameter distribution and rough surface. The analysis of thermal stability, mechanical properties and osmosis performance evaluation indicated nanocapsules prepared by in situ polymerization showed higher decomposition temperature, higher tensile property, lower elastic property and osmosed slowly, which were helpful for storage and usage in self healing materials.A new type of poly(urea-formaldehyde) microcapsules was prepared using urea formaldehyde resin as shell material and modified amine 1618 as core material by interfacial polymerization process. The effects of core/shell mass ratio, the type of emulsifier, mass concentration of emulsifier and stirring speed on w(core), the particle size and distribution of microcapsules were investigated by orthogonal experiment. The particle size, distribution and surface topography of microcapsules were characterized using Nano-2s and scanning electron microscopy. The compositions of microcapsules were characterized using TG-DTA and Fourier transform infrared spectroscopy. Results showed that mold-curing agent of modified amine was encapsulated in the microcapsule and the decomposition temperature of the microcapsules was about 197 ℃. When the core/shell mass ratio was 0.7:1, mass concentration of gum arabic(used as emulsifier) was 1.5 % and stirring speed was 800 r/min, the w(core) was 79.8 %, the mean diameter was 207.5 nm and the microcapsules exhibited uniform round and compact surface.Organic fluorine silane coupling agent were used respectively to modified the microcapsules and the properties of microcapsules were characterized. The results showed microcapsules modified by fluoride silane coupling agent KBM7803 showed good dispersion, organic fluorine and silicon could be grafted to the shell of microcapsule successfully and the thermal stability temperature was improved. When the content of microcapsules modified in epoxy resin matrix was 10 %, the mechanical property of matrix was greatly improved. XPS results indicated that with the increasing of etching depth, the concentrations of organic fluorine reduced gradually, forming a gradient distribution.A fracture-based protocol is established for characterizing healing efficiency of the self-healing epoxy. The fracture load of this composite is measured using a dumbbell-shaped specimen. The addition amount of the fluorine silane coupling agent affect the healing efficiency. When the coupling agent WKBM7803 % = 2 %, the surface of substrate scratch after self-healing was very smooth. The first self-healing efficiency reached 58.9 % and secondary self-healing efficiency reached 53.6 %. Compared with the first self-healing, mechanical properties of epoxy matrix were not decreased obviously after the second self-healing, which could realize repeatedly self-healing. The results of simulation and optimization of active cell distribution and response to migration of crack stress obtained by finite element method showed that in order to achieve the self-healing function, the optimal shell thickness should be between 50-110 nm. The success of this project can provide a simple and possible approach to realize the self-healing function for multiple healing cycles as well as the based data and theory for designing the self-healing anticorrosion coating.