Synthesis of epoxy-loaded poly(melamine-formaldehyde) microcapsules: Effect of pH regulation method and emulsifier selection

Abstract

In this work, epoxy-loaded microcapsules were successfully synthesized by in situ polymerization in oil-in-water emulsion with poly(melamine-formaldehyde) as shell material and diglycidyl ether of bisphenol F resin as liquid core substance. Two synthesis methods were deeply studied and optimized. For each method, different reaction conditions were analyzed by changing the following parameters: emulsifier type (single or binary) and concentration, emulsification conditions and pH adjustment during the polymerization reaction. The morphology, chemical structure, composition and thermal properties were characterized by Scanning Electron Microscopy and Optical Microscopy, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis and Differential Scanning Calorimetry. It was found that the quality, size and surface morphology of the microcapsules depended strongly on the pH adjustment during the in situ polymerization. Moreover, the optimal type and concentration of emulsifier depended on the stage in which the acid pH was adjusted. Spherical microcapsules with different sizes and distributions, improved thermal stability and high core content were obtained by the optimization of reaction parameters and remained stable under more than one year at ambient laboratory conditions. Results indicate that the microcapsules are suitable for the development of self-healing composite materials.