Self-healing microcapsules were synthesized by in situ polymerization with a melamine urea-formaldehyde resin shell and an epoxy resin adhesive. The effects of the key factors, i.e ., core–wall ratio, reaction temperature, pH and stirring rate, were investigated by characterizing microcapsule morphology, shell thickness, particle size distribution, mechanical properties and chemical nature. Microcapsule healing mechanisms in cement paste were evaluated based on recovery strength and healing microstructure. The results showed that the encapsulation ability, the elasticity modulus and hardness of the capsule increased with an increase of the proportion of shell material. Increased polymerization temperatures were beneficial to the higher degree of shell condensation polymerization, higher resin particles deposition on microcapsule surfaces and enhanced mechanical properties. For relatively low pH values, the less porous three-dimensional structure led to the increased elastic modulus of shell and the more stable chemical structure. Optimized microcapsules were produced at a temperature of 60 °C, a core-wall ratio of 1:1, at pH 2~3 and at a stirring rate of 300~400 r/min. The best strength restoration was observed in the cement paste pre-damaged by 30% f max and incorporating 4 wt % of capsules.
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机译：通过使用三聚氰胺脲醛树脂壳和环氧树脂粘合剂进行原位聚合来合成自修复微囊。通过表征微胶囊的形态，壳的厚度，粒径分布，机械性能和化学性质，研究了关键因素的影响，即芯壁比，反应温度，pH和搅拌速率。根据恢复强度和愈合微观结构评估水泥浆中的微胶囊愈合机理。结果表明，胶囊的包封能力，弹性模量和硬度随着壳材料比例的增加而增加。较高的聚合温度有利于较高的壳缩聚度，较高的树脂颗粒在微囊表面上的沉积以及增强的机械性能。对于相对较低的pH值，较少的多孔三维结构导致增加的壳弹性模量和更稳定的化学结构。优化的微胶囊是在温度60°C，核壁比1：1，pH 2〜3和搅拌速度300〜400 r / min的条件下生产的。在预损坏30％f max并掺入4 wt％胶囊的水泥浆中观察到最佳强度恢复。
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