Enhancing flame-retardant properties of epoxy resin using micro-encapsulated boric acid and zinc borate in a urea–melamine–formaldehyde shell.

This work studies the development of multifunctional epoxy coatings that are enhanced with zinc borate and micro-encapsulated boric acid to simultaneously improve their anticorrosive and flame-retardant properties. Microcapsules were developed by encapsulating different concentrations of boric acid and zinc borate in a urea–melamine–formaldehyde (UMF) shell and then incorporating them into an epoxy matrix. The encapsulation allowed for a controlled release mechanism that activated in response to mechanical damage or environmental stimuli. Among the five formulations evaluated, Batch 4 (1.5 g boric acid and 0.5 g zinc borate) performed the best overall. Flame retardancy testing revealed higher UL-94 ratings and limiting oxygen index (LOI) values, with Batch 4 earning a V-0 rating and LOI of 28.5%, compared to V-2 and 23.0% for the plain epoxy. In corrosion testing, Batch 4 showed the best protection, delaying rust formation for more than 500 h in a 3.5-wt% NaCl environment. The UMF microcapsules enabled controlled release of active compounds in response to thermal or mechanical stimuli, ensuring long-term protection. These findings focus on the combined functional benefits of boric acid and zinc borate microcapsules in epoxy coatings, making them strong candidates for advanced protective applications.