Self-Protecting Epoxy Coatings with Anticorrosion Microcapsules

Abstract

The corrosion of steel substrates causes damage that is costly to repair or replace. Current protective coatings predominately rely on environmentally harmful anticorrosive agents and toxic solvents to protect the underlying substrate. The use of lawsone (2-hydroxy-1,4-napthoquinone) together with a water-based epoxy coating provides an environmentally friendly alternative for common protective coatings. Microencapsulated lawsone embedded in an epoxy coating allows the anticorrosive agent to remain dormant until released by damage and delivered directly onto the steel substrate. UV–vis analysis confirms successful encapsulation of lawsone in a polyurethane shell wall and reveals up to 8 wt % lawsone in the capsule cores. Uniform dry film thickness and inflicted damaged are verified with ultrasound and optical microscopy. Visual and electrochemical analysis demonstrates that this self-protective scheme leads to a 70% corrosion inhibition efficiency in a neutral salt water solution.

Acid‐Responsive Anticorrosion Microcapsules for Self‐Protecting Coatings

“…EC tests were performed according to the procedure reported by Odarczenko et al [8] The coated steel substrate was damaged and then immediately submerged in an electrolyte chamber (5 wt% NaCl (≥ 99.5%) solution with pH 1, 2, or 4). The electrolyte chamber was clamped to the coated steel substrate, with the steel substrate acting as the working electrode, a platinum wire as the counter electrode (BASi MW-1032), and a silver/silver chloride electrode as the reference (BASi MF-2052).…”

“…The microcapsules have an average diameter of 14 μm (shell thickness of ≈1 μm, [33,40] measured from SEM images of capsule-embedded coating cross-sections), which is a suitable size for many industrial coating applications. [8,42] The core content of the microcapsules, determined by 1 H NMR, was ≈82 wt% (42 ± 0.8 wt% anticorrosive active, 40 ± 1 wt% CTG, Figures S5-S9, Supporting Information). As the initial concentration of liquid cores was 50 vol% each, a high encapsulation efficiency of 90 ± 2% was obtained.…”

“…Electrochemical Corrosion (EC) analysis was performed on the coatings using potentiodynamic linear polarization experiments to characterize the anticorrosion performance of microcapsule-based coatings. [8,40] In this test, uniformly scribed coatings were subjected to 5 wt% NaCl solution of pH 1, 2, and 4. Characterization of the scribe dimensions is detailed in the Supporting Information (Figures S19 and S20 and Table S1, Supporting Information).…”

“…Tafel extrapolation was used to determine the steady-state corrosion current. [8] Steady-state corrosion currents obtained for control (no capsules) and self-protecting (with 5 or 10 wt% capsules) coatings were used to determine the inhibition efficiency (IE) according to Equation 1 where I o and I i are the corrosion currents for the control and self-protecting samples, respectively. The IE is indicative of the anticorrosion performance of the selfprotecting coating through the reduction in corrosion current.…”

“…Coatings embedded with various types of anticorrosive microcapsules have been reported. Some examples include microencapsulation of alkoxysilanes [7] and lawsone [8] in a polyurethane shell wall, cerium ions released from cerium oxide (CeO 2 ) nanoparticles [9] or natural silica microparticles, [10] methyl benzothiazole released from microgel particles, [11] and calcium nitrate released from cellulose nanofibers. [12] However, these capsules require mechanical damage to trigger their release.…”