Tunable thermal, mechanical, and controlled-release properties of epoxy phenolic novolac resin microcapsules mediated by diamine crosslinkers

Diverse shell structures can endow microcapsules (MCs) with a variety of properties. In this study, four kinds of MCs encapsulated with epoxy phenolic novolac resin (EPN) were obtained using diamines as crosslinkers. The FTIR and CLSM confirmed that the EPN-shell was successfully synthesized. SEM results suggested that all four of the MCs possessed smooth and imporous surfaces, and they displayed uniform size distribution, with the average size ranging from 11.2 to 14.8 μm. Specifically, the MCs synthesized with the crosslinkers of hexamethylene diamine (HAD) and isophorone diamine (IPDA) were more stable and could maintain their spherical shapes in a dry environment, while those synthesized with ethylene diamine (EDA) and triethylene tetramine (TETA) exhibited poorer thermal stabilities and faster release profiles. Lipophilic diamines can form thicker shell thickness, and have smaller d-space values and higher Young's modulus values. Therefore, the lipophilicity of the diamine agents is the key factor that influences the specific properties of the MCs. The hybrid approach was validated as a flexible strategy to meet diverse requirements. The present study can provide a comprehensive understanding of diamine crosslinkers in the synthesis of EPN-MCs, and such MCs can be extended to a wide range of fields because of their broad tunable performance.