Self-healing Anticorrosive Coatings Research Articles

Renewable Polyurethane Microcapsules with Isosorbide Derivatives for Self-Healing Anticorrosion Coatings

Renewable polyurethane microcapsules containing isosorbide derivatives for self-repairing anticorrosion coatings were easily manufactured by interfacial polymerization of a dimer ester–diisocyanate (DE–TDI) prepolymer derived from waste vegetable oil and 1,4-butanediol (BD) as a chain extender using ultrasonication. Two kinds of corrosion inhibitors were also synthesized by the ring-opening reaction of succinic anhydride (SA) or maleic anhydride (MA). Microcapsules having 11–38 μm in diameter were obtained, and the typical core content of microcapsules was around 40–45 wt %. Salt spray tests used for evaluating self-healing anticorrosion coating systems showed significant rust retardancy, depending on the content of the isosorbide derivatives for corrosion control.

Salt spray and EIS studies on HDI microcapsule-based self-healing anticorrosive coatings

Anticorrosive property of hexamethylene diisocyanate microcapsule-based self-healing coatings was systematically investigated by salt spray and EIS measurements. The influences of microcapsule diameter, weight fraction and coating thickness on the anticorrosive performance of the scratched samples were studied under salt spray condition, which revealed the thicker coatings with larger microcapsules at 10wt.% demonstrated the best anticorrosion behavior. Additionally, the kinetics of self-healing process characterized by EIS measurement was parametrically analyzed in an equivalent circuit when the scratched coating was exposed to salt solution. A simplified model was established to explain the influences of these factors with consideration of scratch dimension.

Long-term performance of 1H, 1H′, 2H, 2H′-perfluorooctyl triethoxysilane (POTS) microcapsule-based self-healing anticorrosive coatings

Self-healing anticorrosive coatings were prepared based on the microencapsulation of 1H,1H′, 2H,2H′-perfluorooctyl triethoxysilane (POTS). Toluene played a critical role in the successful synthesis of POTS microcapsules although it was not contained in the resultant capsules. The excellent corrosion-resistant property of a POTS microcapsule-modified silicone elastomer coating was demonstrated by a long-term corrosion test, in which the prepared coating was unscratched and exposed to HCl solution for 1 month, and the metal substrate was inspected after peeling off the coating by scanning electron microscopy and energy dispersive X-ray spectroscopy. In addition, the self-healing behavior of a scribed POTS-based epoxy coating was characterized by an electrochemical impedance spectroscopy measurement when the prepared coating was exposed to NaCl solution. The simulated parametric study from electrochemical impedance spectroscopy equivalent circuit demonstrated the process of corrosion-healing kinetics. The anticorrosive mechanism was proposed based on the self-healing functionality of POTS microcapsules.

High-Resolution SEM with Coupled Transmission Mode and EDX for Quick Characterization of Micro- and Nanocapsules for self-Healing Anti-Corrosion Coatings

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Polyurethane Prepared from Neem Oil Polyesteramides for Self-Healing Anticorrosive Coatings

Polymeric researchers desire strongly to reduce dependency on fossil or petroleum feed stock by utilizing renewable source based polymeric resins in coating. The present research represents the attempt made to develop neem oil (a renewable source) two-pack self-healing anticorrosive polyurethane (PU) coatings cured at room temperature. The oil-based polyesteramide was prepared in two steps; viz., in the first step, oil fatty amide was synthesized, and in the second, it was directly converted to polyesteramide by condensing amide with phthalic anhydride. A spectral study of prepared resin was carried by FT-IR and NMR techniques. Polyesteramide further was utilized for preparation of self-healing PU coatings with incorporation of polyamidoamine based polyurea microcapsules containing natural self-healing agent. The obtained coatings were tested for thermal, physicochemical, and corrosion resistance tests. The coating properties, like gloss, impact resistance, adhesion, and flexibility, were also studied and...

Microcapsule-based self-healing anticorrosive coatings: Capsule size, coating formulation, and exposure testing

Self-healing coatings is a rapidly growing research area, where focus has mainly been on development of new approaches to the mechanism of self-healing. However, there is a growing need for investigation of practical issues related to formulation, application, and testing of true self-healing coatings. In this work, ways of reducing the size of poly(urea–formaldehyde) microcapsules, filled with linseed oil and intended for a microcapsule-based self-healing anticorrosive coating (above water exposure), are explored. The influence of microcapsules on epoxy coating performance is also studied. The actual self-healing effect was not part of this work. The synthesis parameters investigated are stirrer geometry, agitation rate, temperature, and stabilizer concentration. It was found that an increase in stirring rate, correct choice of temperature, and a high stabilizer concentration all caused a decrease in microcapsule size but were accompanied by excessive formation of nanoparticles. Thus, isolation of too large microcapsules has been performed by filtration utilizing a novel low-energy fluoropolymer-coated steel sieve. An estimation of the critical pigment (microcapsule) volume concentration (CPVC) was conducted using gloss measurements and a PVC ladder and found to be about 30vol%. Due to the rather large capsules used (relative to the coating thickness), the low CPVC value can probably be ascribed to a fairly low packing efficiency in the coating, but this needs to be confirmed. Coating performance was evaluated using salt spray exposure and impact testing. Results of the impact testing showed that addition of microcapsules to a binder matrix did not compromise resistance of the coating to mechanical damage and led to formation of fewer and shorter cracks compared to a filler-containing coating. Flaking of the coating was also reduced. Results of the salt spray testing (3 weeks exposure) showed that with an increase of microcapsule content, in the interval 30–50vol%, the extent of corrosion and potential coating delamination decreased and was identical to that of a full commercial anticorrosive coating.

A combined redox-competition and negative-feedback SECM study of self-healing anticorrosive coatings

In this paper, the long-term anticorrosive efficiency of a damaged self-healing coating is studied for the first time using scanning electrochemical microscopy (SECM). In the study an epoxy-coating with embedded-capsules containing a silyl-ester is employed. The properties of the silyl-ester as a healing-agent for the protection of AA2024-T3 were evaluated by complementary SECM experiments operating in negative-feedback and redox-competition modes. The experimental approach here presented allowed for monitoring the early-stages of corrosion activity and subsequent healing mechanisms offered by the release of silyl-ester into a relatively large coating defect. This result was observed by detecting the transition of the oxygen reduction response from a redox-competition mode to a negative-feedback behavior. These measurements demonstrated that the silyl-ester is released efficiently after capsules break upon coating damage, covering relatively large areas and gradually healing the damaged-site hindering the corrosion processes and providing an effective protection for at least one month of immersion in chloride solution.

Self-healing anticorrosive organic coating based on an encapsulated water reactive silyl ester: Synthesis and proof of concept

In this paper a self-healing anticorrosive organic coating based on an encapsulated water reactive organic agent is presented. A reactive silyl ester is proposed as a new organic reactive healing agent and its synthesis, performance, incorporation into an organic coating and evaluation of self-healing capabilities is described. Such silyl esters are good candidates to be used in self-healing anticorrosive organic coating systems since they present the capability to react with water/humidity and metallic substrates, removing thus the need of presence of a crosslinker or catalyst in the system unlike traditional encapsulated approaches. In order to prove the self-healing ability and reactivity of the presented silyl ester encapsulated system, Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET) were used, showing the high capability of these techniques to be used in the development and evaluation of self-healing anticorrosive organic coatings and the good results in corrosion protection offered by the proposed silyl ester healing agent.

Facile microencapsulation of HDI for self-healing anticorrosion coatings

Polyurethane (PU) microcapsules containing hexamethylene diisocyanate (HDI) as core materials are facilely manufactured via interfacial polymerization reaction of commercial methylene diphenyl diisocyanate (MDI) prepolymer and 1,4-butanediol in an oil-in-water emulsion. The resultant capsules have diameters of 5–350 μm and shell thickness of 1–15 μm, both linearly related to the agitation rate in the double logarithm coordinates. The typical core fraction of microcapsules and the yield of synthesis are around 60 wt% and 70 wt%, respectively, while varying with reaction conditions. The effects of parameters including reaction duration and temperature, surfactant concentration, agitation rate, and environmental factors on the formation of microcapsules were systematically investigated and optimized. Quality assessments of each batch of microcapsules were performed using thermogravimetric analysis and scanning electron microscopy. Anticorrosion coatings mixed with synthesized microcapsules were prepared on a steel substrate. Preliminary results indicated significant corrosion retardancy happened in the self-healing coatings under an accelerated corrosion process, showing the great potential of this facile microencapsulation technique in development of catalyst-free, one-part self-healing coatings for corrosion control.

Synthesis of durable microcapsules for self-healing anticorrosive coatings: A comparison of selected methods

Self-healing materials have the ability to ‘repair’ themselves upon exposure to an external stimulus. In the field of coatings, extensive laboratory research has been conducted on these so-called smart materials in the last decade. In the present work, a self-healing concept for epoxy-based anticorrosive coatings, based on incorporation of microcapsules, filled with reactive agents, into the coating matrix, is investigated. Upon small damages to the coating, the reagents are released from the capsules and react, thereby forming a cross-linked network, which heals the crack. However, for the concept to work, microcapsules have to be strong enough to remain intact during storage and coating formulation and application. Furthermore, the capsules must remain stable for many years in the dry coating. Laboratory experiments, using four out of several encapsulation methods available in the literature, have been conducted to investigate the challenges associated with the synthesis of stable microcapsules. It was found that the nature of the core material strongly affects the microcapsule stability and performance. Furthermore, it was evident that experimental procedures developed for certain core materials were not suitable for encapsulation of other compounds without modifications. This is a severe limitation as not many of the encapsulation procedures have been developed for industrially relevant core materials such as epoxy resin. Results of experiments, aiming at finding optimal conditions for robust microcapsule production, are discussed.

Polyelectrolyte complexes as a “smart” depot for self-healing anticorrosion coatings

Various types of “intelligent” self-healing anticorrosion coatings using stimuli-responsive behaviour of polyelectrolyte/inhibitor complexes are presented. Flat nanocomposite multilayers as well as colloidally-templated micro- and nanocarriers with incorporated inhibitor are employed as main building blocks for the formation of novel protective materials. The corrosion inhibitor is incorporated as a structural element (organic molecule), as an inorganic precipitate or in a porous inorganic particle. Being induced by local pH changes during corrosion development, polyelectrolyte/inhibitor complexes afford the unique ability of active feedback and sustained release of inhibitor exactly at the corrosion-damaged sites. Elimination of the corrosive attack returns the complex layer back into the sealed state, providing effective storage and consumption of inhibitor. Insertion of complex-based elements into the coating matrix not only allows the combination of passive and active corrosion protection but also imparts the self-healing properties.

Self-Healing Anticorrosion Coatings Based on pH-Sensitive Polyelectrolyte/Inhibitor Sandwichlike Nanostructures.

An anticorrosion layer of a smart polymer coating is developed. The nature and properties of the coating simultaneously provide three mechanisms of corrosion protection: passivation of the metal degradation by controlled release of an inhibitor, buffering of pH changes at the corrosive area by polyelectrolyte layers, and self-curing of the film defects due to the mobility of the polyelectrolyte constituents in the layer-by-layer assembly.