Effect of processing conditions on the microencapsulation of 1-methylimidazole curing agent using solid epoxy resins

Abstract

Among various methods for preparation of the non-reactive or latent curing agents for epoxy resins, encapsulation offers a promising and cost-effective method. This system has been used in one-part thermosetting adhesives or prepregs for developing advanced composite materials. In this study, 1-methylimidazole (1-MI) was microencapsulated using solid epoxy resins via solvent evaporation method. The effect of various types of shell materials or solid epoxy resins, different core-to-shell ratios of 30/70, 50/50, and 70/30, and a variety of mixing rates (500, 1000, and 1500 rpm) on the preparation of microcapsules were evaluated. The 1-MI content and microencapsulation efficiency were calculated using thermal gravimetric analysis (TGA). The shape and surface morphology of the prepared microcapsules were evaluated using scanning electron microscopy (SEM) technique. Gel time of the microcapsules mixed with liquid epoxy resin was also investigated. Results showed that by decreasing the core-to-shell ratio at different stirring rates, the encapsulation efficiency increased. The microencapsulation efficiency of 34.8% was obtained at shell-to-core (1-MI) ratio of 70/30 at stirring rate of 500 rpm. The results also showed that at higher mixing rates, 1-MI content in microcapsules was controlled by high shearing force. It has been found that the gel time of the epoxy resin/microcapsule samples was proportional to the imidazole content and it was in agreement with the data obtained by TGA analysis, as well.