Synthesis and characterization of high durable linseed oil-urea formaldehyde micro/nanocapsules and their self-healing behaviour in epoxy coating

In this study, Urea-Formaldehyde (UF) capsules containing linseed oil were prepared via in-situ polymerization and then dispersed in epoxy coating with different capsule contents. An innovative method to maintain of capsules was proposed which enhance the durability and ease of dispersion in the coating. The capsules were synthesized with three different reactor mixing rates and its effects on the capsules morphology, thermal properties and size distribution, as well as on the state of dispersion in the epoxy coating and self-healing performance were surveyed. Synthesized capsules had trimodal distribution in the range of 3 nm to 238 μm and depending on the mixing rate; the average size of the capsules was changed. The core content of the capsules was between 59% and 96% which depends on stirrer speed. Fourirer transform infra-red (FTIR) spectra and thermal gravimetry analysis (TGA) thermograms confirmed that the linseed oil was successfully encapsulated in the UF shell. Capsules morphology, distribution and dispersion state of capsules in the self-healing coating were examined via scanning electron microscopy (SEM) and optical microscopy which verified that capsules have good dispersion and distribution in the epoxy coating. Healing of scratched coating was confirmed by optical microscope and salt spray test. The results of the salt-spray test revealed a proper corrosion resistance of self-healing coating compared to the coating without microcapsules.