Water tree damage self-healing properties of plasma modified tri-layer shell-nucleated microcapsules/cross-linked polyethylene composites

This paper proposes a self-repairing material for cross-linked polyethylene (XLPE) based on a microcapsule system to solve the problem of insulation degradation caused by water tree aging. The microcapsules are extrinsic self-healing systems, which not only have good stability and high repair rates but also have little impact on the performance of the matrix. Plasma-modified tri-layer shell-nucleated microcapsules/XLPE composites were prepared by room temperature air radio frequency plasma discharge, and their insulation properties were tested to analyze the effect of microcapsule doping content on material properties. The accelerated water tree aging experiment was carried out by water needle electrode method, and the repair capability of microcapsules to water tree damage area before and after plasma modification was analyzed. The results show that compared with pure XLPE samples, when the content of microcapsules is 1.0 wt. %, the AC breakdown field strength and DC conductivity of the composites change little, and the dielectric properties of composites are improved. When the water tree breaks the microcapsule wall, due to the capillary effect, repair solution and catalyst flow into the water tree branch damage channel and react with water to repair the water tree damage. The average water tree length of plasma-modified microcapsules/XLPE specimens after water tree aging was reduced by 24.86% compared to non-plasma-modified microcapsules/XLPE specimens. The outermost layer of plasma modified microcapsules is nano-SiO2 modified by plasma hydroxylation, which can graft more silane coupling agents, so that the distribution of microcapsules in XLPE matrix is more uniform, the agglomeration of microcapsules is reduced, and the water tree repair ability of composite materials is improved.