Self-healing nanocomposites comprised of poly(urea formaldehyde) nanocapsules in a thermosetting polyurea

Abstract

In this study, poly(urea formaldehyde) (PUF) nanocapsules with epoxy cores were blended into a polyurea matrix, formulated as poly[(phenyl isocyanate)–co-formaldehyde] (PMDI) (f = 3.4), and a diamine curing agent (VERSALINK 650) to form nanocomposites. The nanocomposites were then subjected to impact delamination tests at temperatures below −74 °C. Scanning electron microscopy was used to qualitatively inspect the nanocomposites before the impact (virgin), after the impact, and after self-healing. Dynamic mechanical analyzer measurements were carried out to characterize the mechanical properties of the nanocomposites. Specifically, their stiffness was characterized by the storage modulus, and damping by the loss modulus. The influence of the curing agent and the loading concentration of the PUF nanocapsules on the morphology and mechanical properties of the nanocomposites were investigated in order to optimize the cure rate, distribution, and loading concentration of the PUF nanocapsules in the polyurea matrix. It was found that when 1 wt% PUF-epoxy nanocapsules were loaded into the polyurea, the recovery of the storage modulus after impact, which was used to characterize self-healing, was found to be 32 ± 1% and 56 ± 1% after 3 and 30 days, respectively.