Self-healing Properties Of Magnetic Targeting UV-polymerization Microcapsule/epoxy Resin Insulation Composite

Epoxy resin,as an important basic insulating material,is widely used in electric power equipment,electronic devices and other fields.Under long-term operating conditions,it inevitably bears the effects of mechanical,electric field and thermal stress,and produces tiny cracks and electrical tree damage,which seriously affects the service life of equipment and devices,and even leads to premature failure.It is a challenging but significant task to quickly inhibit and repair the mechanical damage and electrical tree damage of epoxy resin insulation materials.To solve this problem,this paper bypassed the traditional technical route of nano-modification of insulating materials to inhibit electrical tree,and based on microcapsule self-healing system,magnetic targeting UV-polymerization microcapsules were prepared by solvothermal method,St（?）ber method and interfacial polymerization method.The microcapsule/epoxy resin composite insulating material was constructed by high temperature curing method,and the performance parameters,electrical characteristics and self-repairing characteristics of the prepared materials were investigated by experiments and the mechanism of self-healing was analyzed.The main research work of this paper is as follows,（1）The core-shell Fe₃O₄@SiO₂ magnetic targeting nanoparticles were prepared by solvothermal method and St（?）ber method.The magnetic targeting UV-polymerization microcapsules were formed by interfacial polymerization of cationic photosensitive epoxy core material and modified polyurethane shell material.The microstructures and basic physical properties of the prepared samples were analyzed and characterized.It was found that the core-shell Fe₃O₄@Si O₂ nanoparticles had a uniform particle size distribution（average particle size of 182.64 nm）and good dispersibility.The execllent magnetic properties（magnetic saturation strength of 52.86 emu/g）were maintained while the good insulating properties（volume resistivity increased by seven orders of magnitude）were exhibited.The prepared microcapsules had uniform size（average particle size 99.19μm）,good coating effect,and high core material content（75 wt%）.The polyurethane（PU）based shell composed of Ti O₂ and Fe₃O₄@Si O₂ nanoparticles exhibited good UV shielding performance.At the same time,the release of harmful substances from the microcapsules was extremely low,far below the relevant environmental protection standards.（2）The magnetic targeting UV-polymerization microcapsule/epoxy composite insulation material was synthesized through high temperature curing.We tested the mechanical,dielectric and insulating properties of the composites,and then analyzed their corresponding influence mechanisms.From the experimental results,it can be demonstrated that microcapsule doping can enchance the mechanical characteristic of the matrix.And at low doping concentration（<5 wt%）,the synergistic effect of the interpenetrating network structure and the charge trap makes up for the effect brought by the microcapsule introduction,and the composite material still maintains good dielectric performance（the dielectric constant is less than 4.1748 at the measurement frequency of 50 Hz）and excellent insulation breakdown performance（the effect of the microcapsule introduction on the matrix breakdown performance can be basically ignored,and the side effect is less than 3%）.（3）Based on the electrical treeing test platform,the development of electrical tree in epoxy resin composites was observed,and the repair effect of mechanical/electrical tree damage in composites was characterized,and its self-healing mechanism was revealed.The results show that,for physical damages,composite samples with targeted distribution of microcapsules have higher repair efficiency and lower material cost than composite materials without targeting.Moreover,due to the good fluidity of core repair agents,scratch damage channels can be filled in a short time,which can meet the needs of timeliness.For electrical tree damage,the introduction of microcapsule will not cause the change of electrical tree initiation voltage of composite materials,and maintain the excellent electrical tree resistance of epoxy substrate;When the electrical tree breaks the microcapsules,the capsule core repairing agent entering the damaged channel has a good repair effect on the electrical tree damage under the action of in-situ electroluminescence,and the insulation performance of the composite sample can be restored to 97.8%of that without damage.