Abstract
In this work, poly (urea-formaldehyde-melamine) (PUFM) microcapsules containing a commercial epoxy ester resin were synthetized by in-situ polymerization technique. The microcapsules size distribution was analyzed by laser diffraction and the obtained microcapsules were evaluated by the Fourier-transform infrared spectroscopy (FTIR), in order to prove the ester epoxy resin microencapsulation. The filled microcapsules were incorporated in an epoxy three layer coating system, varying the microcapsules concentration (10 % and 15 %) and the microcapsules incorporation on the different layers - first, second or both. The coatings electrochemical behaviors were evaluated by electrochemical impedance spectroscopy (EIS) technique and localized scanning vibrating electrode technique (SVET). Pull-off adhesion tests were performed in the coatings systems, in order to verify if the microcapsules presence did affect the adhesion and/or cohesion coating properties. The EIS results showed that microcapsules change the coating electrochemical response, but the samples visual aspect suggests that the microcapsules improve the barrier properties of the microcapsules systems. The coating system containing the microcapsules showed a significant self-healing effect when stressed by a mechanical defect and the higher concentration (15 wt. %) of microcapsules provided a better self-healing protection, with better anticorrosive performance. Additionally, the microcapsules did not disturb the adhesion/cohesion properties of the coating system.
Highlights
The use of coatings is the most popular corrosion protection method, to protect metallic surfaces against aggressive species
The electrochemical impedance spectroscopy (EIS) diagrams show that the presence of the self-healing particles in the coating system affected the anticorrosive barrier properties
The traditional coating—without microcapsules—presented values around 1.88 × 109 ohm·cm2, whereas the self-repairing coatings presented values in the range 8.63 × 107–1.99 × 108 ohm·cm2, after 6 h of immersion. This perturbation of the microcapsules in the coating systems is probably related to the presence of microcapsules larger than 20 μm that normally causes a decrease in the barrier properties of any coating creating some preferential pathways for the electrolyte inside the coating
Summary
The use of coatings is the most popular corrosion protection method, to protect metallic surfaces against aggressive species. The damaged samples were exposed to room air for 48 h after the defect was made to permit there was time to cure and reticulate the epoxy ester resin released from the core of the microcapsule by contact with the oxygen in the air. The samples were allowed to stay in the laboratory atmosphere for 48 h before the SVET measurements have been performed This time is sufficient to promote the polymerization by air O2 in order to obtain a protective film in the defect region. For SVET measurements only one layer of 200 μm thickness were applied because for a complete system of about 600 μm thick, it would be impossible to detect ionic currents coming from such long distance in defect area In such terms, only three conditions have been evaluated: (1) without microcapsules; (2) with 10 wt.
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