Mechanical properties of melamine formaldehyde microcapsules for self-healing materials

Microcapsules containing a self-healing agent may be incorporated into functional materials to maintain their mechanical strength after a crack is generated. Such microcapsules should have optimum mechanical strength. In this work, microcapsules were formulated by encapsulating dicyclopentadiene (DCPD) with a shell of melamine formaldehyde (MF). The morphology of the microcapsules was characterised using optical microscopy and environmental scanning electron microscopy (ESEM). The shell thickness of the microcapsules was measured using transmission electron microscopy (TEM). Their size distribution was quantified using Malvern particle sizing. Furthermore, their mechanical properties were determined using a micromanipulation technique. Results showed that DCPD was successfully encapsulated by melamine formaldehyde. The mean diameter of the microcapsules varied from 10.7 to 16.0 μm, depending on agitation speed which was used in generation of DCPD (oil)/MF precondenstate (aqueous) emulsion. The mechanical strength parameters including rupture force and nominal rupture stress were found to vary with their size and the reaction time of in situ polymerisation of MF.