Synthesis and characterization of amine hardener filled microcapsules for self-healing composite applications

Materials experience microcracks during service conditions and thus might not fulfil their functionality. Hence there is a necessity to develop a method which enhances the functionality of the material without affecting its inherent properties. Self-healing of materials through microencapsulation repairs microcracks and extends the service life of material. In this work, amine hardener encapsulated polymethyl methacrylate (PMMA) microcapsules were synthesized using oil-in-water solvent evaporation technique. Various process parameters such as surfactant concentration, operating temperature, agitation speed and core to shell ratio were investigated to get the desired morphology and healing agent content. The challenges faced during the synthesis of microcapsules were reported. It was observed that solvent evaporation rate, stirring duration, surfactant type and concentration have an impact on the agglomeration of capsules. The molecular architecture, thermal stability and surface morphology of the microcapsules were characterized by Fourier-transform Infrared spectroscopy (FT-IR), Thermogravimetric analysis (TGA) and Scanning Electron Microscope (SEM) respectively. Core content of the capsules was evaluated by solvent extraction method and the capsules average size and size distribution were reported. The effect of different surfactants and their combinations such as Polyvinyl Alcohol (PVA), Tween 80 and (Tween 80 + PVA) on the microcapsules synthesis were reported. This study also reported the influence of surfactant concentration on the microcapsule shell thickness, which is a critical parameter in evaluating structural healing efficiency. Developed microcapsules ability to release core content and repair micro cracks was verified qualitatively with 3D optical microscope.