A Dual-Functional Surfactant Strategy for High-Yield Synthesis of Epoxy-Loaded Melamine Formaldehyde Microcapsules

Articles in Press

Document Type : Original Article

Authors

1 Institute for Color Science and Technology

2 Faculty of Surface Coatings and Novel Technologies Department of Resins and additives, Institute for Color Science and Technology,

Abstract

The encapsulation of various healing agents can be achieved using amino resins as the shell material. For optimal encapsulation efficiency, pH adjustment is a critical parameter. In this study, epoxy resin was encapsulated via in-situ interfacial polymerization in an oil-in-water emulsion. A dual-functional surfactant featuring a quaternary ammonium moiety serving as the hydrophilic head group, combined with precise pH control, was employed. In addition to catalyzing amino resin formation at the interface, this surfactant significantly suppresses the formation of unwanted nanoparticles. Furthermore, citric acid, used for pH adjustment, also acts as a surfactant due to its structural properties, preferentially localizing at the epoxy/water interface. As a result, a high encapsulation efficiency of 92% is achieved, which displays an improvement of about 25% over conventional ammonium chloride-catalyzed methods. The core-to-wall ratio was systematically optimized, with a 1:2 ratio yielding the highest encapsulation efficiency (92%), while a 1:3 ratio led to a 15% efficiency drop. Furthermore, stirring rate modulation enabled size control, producing capsules ranging from 1 μm (at 1100 rpm) to 2 μm (at 500 rpm). Surfactant concentration critically influenced unwanted nano particle formation and encapsulation efficiency where, using 1 wt% of surfactant, a 92% encapsulation efficiency was achieved, while concentrations at 10 wt% caused a 28% efficiency decline due to excessive aqueous-phase polymerization and capsule aggregation. This work establishes a comprehensive framework for microcapsule synthesis, enabling the design of tailored microcapsule for high-performance self-healing applications.

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Main Subjects

Progress in Color, Colorants and Coatings

Articles in Press, Accepted Manuscript
Available Online from 27 October 2025

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