Study On Self-healing Material With Epoxy-containing Microcapsules And Imidazoline Derivatives Curing Agent

Local damage and microcrack will inevitably generate within polymercomposites during the usage, leading to the decrease of the material's mechanicalproperties. Therefore, a timely healing on the microcrack is critical for the polymercomposites. Currently, research on the self-healing of microcapsules emphasizes onnormal temperature cured composites. At a relatively high temperature, maintainingthe activity of healing agent in the microcapsule core is an important issue. In thisarticle, appropriate latent curing agent is selected to address this problem. Polymercomposites doped with self-healing microcapsules show great developing potentialand application prospect in the area of aeronautics and astronautics.In this article, a dual self-healing system is studied, which contains epoxycontainingmicrocapsules and imidazole derivatives (2MZ-Azine) as the latentcuring agent. The microcapsules and 2MZ-Azine are evenly doped into the resinmatrix. When the microcapsules are ruptured during the propagation of microcrackthrough the material, the epoxy resin in the core of microcapsules will be releasedand exposed to 2MZ-Azine in the matrix. After heated to a certain degree, catalyticpolymerization reaction will be triggered and the self-healing of crack surface isachieved simultaneously. Since the material coherence between healing agent andcomposite matrix, the adhesive interface of crack will match well.The research in this article is based on the synthesis of epoxy resinmicrocapsules. By applying in- situ polymerization reaction, the microcapsules areprepared with urea-formaldehyde resin as wall material, epoxy resin E-51 andreactive diluent Trimethylolpropane Triglycidyl Ether (TMPEG) as core material.Based on the exploratory experiments, orthogonal tests are designed to optimize thesynthesis process and investigate the influence of different synthesizing variableson the properties of microcapsules. It is concluded that the optimized synthesizingmethod has a material ratio (core to wall in weight) of 1.4:1, agitating rate of 250r·min-1, acidification time of 3h and DBS as the emulsifier. In order to demonstratethe morphologies and properties of microcapsules, infrared spectroscopy (IR)analysis, optical microscopy (OM) and scanning electron microscopy (SEM) arealso applied in the experiments. The results show that the microcapsules surfacesare dense and less cluster of urea-formaldehyde is observed. Additionally, thecontent of core (61%), production rate (80%), size distribution (80~430μm),average particle size (255μm), wall thickness (6-10μm) are also worked out. The controlled release ability, and wettability between the microcapsule core and wall are suitable for the usage.After analyzing the curing mechanism of E-51 and 2MZ-Azine, the healing efficiency of the self-healing system is tested in a pure epoxy resin matrix. It is found that with particular microcapsules size and core content, the content of microcapsules and curing agent has great influence on the healing efficiency. On the other hand, when the content of latent curing agency exceed the minimum concentration to trigger the polymerization of anion, the distribution of microcapsules and curing agent will greatly influent the healing efficiency, while the curing agent content shows no influence. The maximum healing efficiency (86%) will be realized when the microcapsules content is 15% and curing agent content is 2%. The self-healing of microcrack is experimentally proved by observing the cross section of the healed composite after secondary fracture.