Effect of mixing mode and emulsifying agents on micro/nanoencapsulation of low viscosity self-healing agents in polymethyl methacrylate shell

In this study, epoxy prepolymer (EC 157) and pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) as hardener were encapsulated separately in polymethyl methacrylate (PMMA) shells through an internal phase separation method. Chemical structures, morphologies, and thermal properties of healing agent micro/nanocapsules were characterized by Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), and thermal gravimetric analysis (TGA) respectively. The effects of encapsulation processing conditions such as mechanical mixing rate, ultrasonication, emulsifier type, and co-emulsifier concentration on encapsulation yield, capsule mean diameter and core content were studied using the Taguchi experimental design approach. The results indicated that the main significant factors affecting the yield of encapsulation are emulsifier type and ultrasonication. The most important factors which affect the mean diameter of capsules are emulsifier type and mechanical mixing rate. The core content was influenced by ultrasonication and mechanical mixing rate. The relative optimum condition of encapsulation was also determined using overall evaluation criteria.