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Dr. Seyed Mirabedini

Eastern Michigan University

Synthesis of Microcapsules Containing Epoxy and Vinyl Ester Resins and Their Possible Applications in Self-Healing Coatings and Thread Locking Adhesives

Abstract

In this study, gelatin-gum Arabic/polyurea-formaldehyde microcapsules containing vinyl ester resin (VER) and benzoyl peroxide initiator (BPO), as well as dual-layer urea-formaldehyde/polyurethane based microcapsules polyurethane/urea- microcapsules comprising active epoxy resin were synthesized. Either VER or BPO filled microcapsules were prepared in two steps using complex coacervation followed by in-situ polymerization routes, respectively, at 500 and 700 rpm mixing speeds. Dual-layer microcapsules containing epoxy resin were synthesised via in-situ polymerization method in an oil-in-water emulsion at 500 and 700 rpm mixing speeds. Optical microscopy, scanning electron microscopy (SEM), thermogravimetry analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the synthesized microcapsules. Corrosion resistance and healing property of microcapsules (either VER/BPO or active epoxy resin) embedded epoxy-based coatings were studied by utilizing the healing performance of scribed areas and the natural salt spray corrosion test, respectively.

Thread locking adhesive (TLA) samples containing two different types of microcapsule systems were prepared and well-dispersed in a thermoplastic media. A thermoplastic resin component also consisted of a mixture of solvents, additives, fillers and, the hardener of microencapsulated resin (amine compounds for epoxy-based systems). At the time of application, the screw surface was pre-coated with microcapsule embedded thread locking compounds and set after microcapsule breakage during fixing nuts.

The regular spherical microcapsules were successfully prepared with a diameter of 50-350 µm and shell thickness of 0.5-1.8 µm. Optical microscopy showed that the synthesized microcapsules have proper stability over time in the solvent. FTIR spectroscopy revealed the absence of free isocyanate groups in the microcapsule’s shell. The FTIR spectroscopy, SEM and optical microscopic confirmed the successful synthesis of microcapsules. The results confirmed improving healing properties and corrosion resistance of microcapsule embedded epoxy-based coating. The strength of the capsular adhesive at 50-60 wt% of microcapsule loading revealed about 15-18 N.m. The Results revealed the novel microcapsules synthesized in this study present an attractive outlook for applications in self-healing coatings as well as in thread locking adhesives.

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