Synthesis of double-shell microcapsule containing MOF as the curing agent of epoxy resin

Abstract

Microcapsule-type curing agents that have a single polymer shell encounter challenges due to the inadequate airtightness of the shell material, which affects the storage stability of the epoxy resin (EP) once it has been mixed. In this work, a microcapsule-type latent curing agent with an extended storage period was successfully prepared by introducing a metal-organic framework (MOF) as its second-layer shell. Imidazole (Im), as a curing agent, was initially encapsulated in polyurethane (PU) via the interfacial polymerization to form the single-shell microcapsule (Im@PU), in which different morphologies and core contents (IPM1-7) were obtained by adjusting the mass ratio of the core to shell. The optimal formulation, designated as IPM2, was determined due to its smooth surface and uniform size distribution. Subsequently, ZIF-8 was co-coordinated and grown on the surface of IPM2 to form a double-shell microcapsule-type curing agent (Im@PU@ZIF-8). The Im@PU@ZIF-8 exhibits delayed kinetic behaviors and enhanced storage stability. Notably, the Im@PU@ZIF-8 can be reliably stored for over 35 days at 40 °C. Meanwhile, the shell material ZIF-8 can be employed as a functional filler to enhance the mechanical properties of epoxy composites. This feasible strategy develops innovative ideas for the EP-latent curing agent systems and aims to establish a general method.