Tung oil: An autonomous repairing agent for self-healing epoxy coatings

The capability of the encapsulated Tung oil was investigated as a scratch healing agent for self-healing coatings. Encapsulation of Tung oil with urea–formaldehyde shell was carried out by in situ polymerization. Before the mechanical agitation of microcapsules into epoxy resin, their characteristics were evaluated by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). Released Tung oil from ruptured microcapsules healed the artificial scratch in the coating matrix successfully. Corrosion resistance of healed area was evaluated by electrochemical impedance spectroscopy (EIS) and immersion test; and the results were compared with neat epoxy coating.     

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 30 vol%. 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 30–50 vol%, the extent of corrosion and potential coating delamination decreased and was identical to that of a full commercial anticorrosive coating.     

Self-lubricating epoxy composite coating with linseed oil microcapsule self-healing functionality

Cured epoxy resins have poor abrasion resistance, which shortens the service life of the material. This work aims to improve the tribological properties of epoxy resins by coupling self-lubrication and auto-healing. In this study, linseed oil microcapsules with an average particle size of 38.57 μm and good thermal stability were successfully prepared by in situ polymerization. The effects of microcapsule content on the tribological, mechanical, and self-healing properties of the composite coatings were studied. It was demonstrated that the composite coating has outstanding self-lubricating properties. The coefficient of friction reduced from 0.634 (pure epoxy resin) to 0.0459 (epoxy resin with 10 wt.% linseed oil microcapsules). Wear rate reduced from 7.16 × 10⁻⁴ mm³/(N m) to 1.74 × 10⁻⁵ mm³/(N m). The self-lubricating mechanism of the coating was investigated by SEM and EDS, which indicated that the formation of uniform and continuous lubricating film on the surface of the friction pairs was the key to improving the wear resistance of the material. In addition, the linseed oil released after the microcapsules rupture can repair the abrasion marks by reacting with oxygen during the friction process. The dual-functional effect of linseed oil microcapsules prolongs the life of epoxy resin coating and expands its application range.     

自修复微胶囊及其防护涂层应用研究进展

随着自修复技术的不断发展,微胶囊在防护涂层等领域日益表现出突出的应用优势。文中综述了单壁、双壁自修复微胶囊的配方设计与结构性能以及微胶囊的模拟仿真研究现状,综述了以异氰酸酯、环氧树脂、缓蚀-腐蚀抑制剂、植物油为修复剂的自修复微胶囊在防护涂层中的应用研究进展,总结了现有微胶囊自修复材料存在的问题,提出了将自修复微胶囊与分子动力学模拟相结合的研究方法,希望通过该方法建立微胶囊宏微观结构与性能的关联性规律,实现对微胶囊自修复机理的深入探索与研究。     

Self-healing ability and adhesion strength of capsule embedded coatings—Micro and nano sized capsules containing linseed oil

Urea–formaldehyde (UF) capsules were synthesized in micro and nano sizes, containing linseed oil (LO). The micro- and nanocapsules were incorporated through epoxy coatings and the coatings were applied on C-steel panels. Then the self-healing performance of the coatings was investigated. The corrosion resistance, adhesion strength and its retaining after immersion of nanocapsule incorporated coatings were compared with the optimum microcapsule incorporated ones.     

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 10 wt.% 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.     

Preparation of Tung Oil-Loaded PU/PANI Microcapsules and Synergetic Anti-Corrosion Properties of Self-Healing Epoxy Coatings

Tung oil is used as a catalyst-free repair agent. Tung oil-loaded polyurethane (PU) microcapsules are prepared by interfacial polymerization in a SiO₂-stabilized Pickering emulsion system, polyaniline (PANI) is deposited in situ on the PU microcapsule surface, and tung oil-loaded PU/PANI double-layer shell microcapsules are obtained. Synthesized PU/PANI microcapsules showed the characteristic dark-green color of conductive PANI. The average particle size is 31.1 ± 8.1 µm and the core content is 45.1 ± 4.3 wt%. The microcapsules have a good thermal stability, and the chemical structure of the PU/PANI wall and tung oil core is confirmed by Fourier transform infrared analysis. Self-healing anti-corrosion coatings are prepared by adding 10 wt% microcapsules into epoxy resin. The corrosion resistance properties of the self-healing coating are evaluated by immersing scratched coatings in 10 wt% NaCl solution for 15 days. The self-healing coating with 10 wt% tung oil-loaded PU/PANI microcapsules have the best anti-corrosion property, and slight corrosion do not occur until 15 days after immersion in salt solution. The self-healing and anti-corrosion mechanism are revealed. The tung oil core and the PANI wall of microcapsules contributed synergistically to the excellent self-healing and anti-corrosion properties of the coating through the formation of self-healing films and passivation layers.     

Self-healing coatings for steel

The efficacy of a “self-healing” corrosion protection coating system for use on steel enclosures for outdoor equipment has been investigated using urea formaldehyde microcapsules (50–150 μm in diameter) containing several types of film forming compounds (healants) and corrosion inhibitors mixed into commercially available coatings systems. Five different types of inhibitors/film formers were tested, and three different techniques for application of the coatings with microcapsules were evaluated. Laboratory tests showed that when the coating system was damaged by abrasion, the microcapsules released the film forming and corrosion inhibiting compounds. Steel substrates coated with these self-healing systems were scribed and laboratory tested according to ASTM D 5894. Undercutting at the scribe (ASTM D 1654) was reduced by using microcapsules containing self-healing compounds. Growth of coating damage at the scribe was arrested in self-healing coatings with all microcapsule formulations compared to control samples. The performance of some microcapsules evaluated in this study was found to be dependent on the method of application.     

Synthesis and characterization of phenol–formaldehyde microcapsules containing linseed oil and its use in epoxy for self‐healing and anticorrosive coating

Phenol–formaldehyde microcapsules with linseed oil as an active agent were produced by applying in situ polymerization method. The anticorrosion and self‐healing efficiency of the synthesized materials were studied. Characteristics of these synthesized capsules were studied by Fourier transform infrared spectroscopy, and surface morphology was analyzed by using scanning electron microscope. Controllable particle size was estimated at different rpm of stirrer and particle size was checked under microscope and also by using particle size analyzer. The anticorrosion performance of encapsulated microcapsules coated with epoxy resin was carried out in 5% NaCl aqueous solution. The effectiveness of linseed oil filled microcapsules was investigated for healing the cracks generated in paint films or coatings. It was found that the cracks were successfully healed when linseed oil was released from ruptured microcapsules. Further, linseed oil‐healed area was found to prevent effectively the corrosion of the substrate in immersion studies. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Development of self-healing coatings based on urea-formaldehyde/polyurethane microcapsules containing epoxy resin

In this study, the synthesis of urea-formaldehyde/polyurethane (UF/PU) microcapsules containing epoxy resin for self-healing and anti-corrosion coatings with good stability has been reported. Spherical microcapsules were prepared with a diameter of about 50–720 μm and a shell thickness of 0.6–0.7 μm via in situ polymerization in an oil-in-water emulsion using 2,4-toluene diisocyanate-based pre-polymer along with the urea-formaldehyde. Scanning electron microscopy (SEM) and optical microscopy (OM) were employed to evaluate the shape and morphology of the microcapsules. Fourier transform infrared (FTIR) spectroscopy showed the absence of free isocyanate groups within the microcapsule shell confirming the completion of shell formation reactions. OM illustrated that the microcapsules were stable over a period of 30-days in toluene and xylene. Increasing microcapsule loading improved crack repairing and anti-corrosion performance of the coating layer. Low-carbon steel coupons coated with an epoxy resin containing 10 wt% microcapsules and scribed using a scalpel blade showed no visible sign of corrosion after up to 5 weeks of exposure in a standard salt spray test chamber.     

自修复聚脲甲醛微胶囊的制备及成囊机理研究

采用原位聚合法制备了自修复聚脲甲醛包覆环氧树脂微胶囊。考察了原料用量、反应温度、酸化值和固化时间等对微胶囊粒径分布和表面形态的影响,确定了微胶囊的最佳制备工艺。借助显微镜实时监测微胶囊化过程,探讨了微胶囊的成囊机理,并将微胶囊填充到脲醛树脂中。结果表明:采用最佳制备工艺制得的微胶囊包覆率较高、结构紧密、粒度均匀,室温下保存一周后没有出现团聚和破裂;将9%微胶囊添加到脲醛树脂中,微胶囊分散均匀,脲醛树脂复合材料的韧性得到提高。     

Self-healing epoxy coatings loaded with inhibitor-containing polyelectrolyte nanocapsules

The self-healing polymer coatings containing organic corrosion inhibitors are intensively investigated as an alternative for highly toxic Cr(VI)-based systems. Protective self-healing coatings are realized by embedding “smart” containers, able to release a corrosion inhibitor under some specific conditions occurring when the corrosion process starts (e.g. on pH change) or upon a mechanical damage. In this study a system with the corrosion inhibitors (2-methylbenzothiazole (BT) and 2-mercaptobenzothiazole (MBT)) encapsulated inside the polyelectrolyte nanocapsules embedded in the water-based epoxy coatings is tested for its self-healing performance. The nanocontainers were prepared by the electrostatic adsorption of polyelectrolytes directly on the oil phase drops containing the inhibiting agent. The results for BT emulsion droplets and the mixture of BT and MBT encapsulated by docusate sodium salt/poly(diallyldimethylammonium chloride) (AOT/PDADMAC) and docusate sodium salt/poly(diallyldimethylammonium chloride)/poly(styrene sulfonate) (AOT/PDADMAC/PSS) surface complexes are presented.The X-ray Photoelectron Spectroscopy (XPS) was used to confirm the release of the inhibitor from the scratched coating. The influence of the nanocapsules on the barrier properties and self-healing performance of the epoxy coatings were tested by electrochemical impedance spectroscopy (EIS) in NaCl solution, the salt spray test (SST) according to ISO9227 and filiform corrosion test (FFT) according to EN ISO 3665. Potential blistering was rated according to EN ISO 4628-2.     

Self-healing and anticorrosive properties of Ce(III)/Ce(IV) in nanoclay–epoxy coatings

The self-healing and anticorrosion effects of cerium nitrate in epoxy–clay nanocomposite coatings systems were studied. Different amounts of cerium (III) were added to epoxy–montmorillonite clay composites and the nanocomposite coatings were prepared and applied on cold rolled steel panels. Ultrasonication was applied to disperse the nanoclay into the epoxy cerium nitrate composition. Electrochemical impedance spectroscopy (EIS) was used to study the self-healing and anticorrosion behaviors of the coatings. The structure of the dry coating and the protective mechanism of the pigments in the coating were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) analysis and field emission electron microscopy (FESEM). Transmission electron microscopy (TEM) illustrated the separation of clay layers which interacted with the epoxy resin. Electrochemical impedance data indicated that the epoxy cerium (III)–montmorillonite nanocomposite coatings were superior to the epoxy coatings in corrosion protection properties. The self-healing behavior of such coatings was due to the presence of cerium nitrate that could be released at the defects within the coating and hindered the corrosion reactions at the defective sites. It was shown that the best corrosion protection was achieved with nanocomposite coatings containing 4 wt% clay and 2 wt% cerium nitrate.     

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.     

Corrosion study of hybrid sol–gel coatings containing boehmite nanoparticles loaded with cerium nitrate corrosion inhibitor

To improve the corrosion protection of sol–gel derived hybrid silica/epoxy coatings containing boehmite nanoparticles, inorganic corrosion inhibitor was introduced into the coating via encapsulation in the nanoparticles. The morphology and chemical structure of the deposited films were studied by Scanning Electron Microscopy (SEM) and Fourier Transformed Infra-red Spectroscopy (FT-IR). The anticorrosion and self-healing properties of the coatings were evaluated by Electrochemical Impedance Spectroscopy (EIS). The high corrosion resistance performance of such coatings is due to the presence of encapsulated cerium nitrate corrosion inhibitor that can be released at the defects within the coating, hindering the corrosion reactions at defective sites.     

High-performance self-healing anticorrosion epoxy coating based on microencapsulated epoxy-amine chemistry

Attributed to the merits of excellent material compatibility, healing performance, and long-term stability, the self-healing system based on microencapsulated epoxy-amine chemistry is a potentially practical self-healing system for both structural and functional materials. Herein, based on the microencapsulated epoxy-amine chemistry, a self-healing anticorrosion coating was successfully developed. This self-healing coating system was modeled theoretically to explore the factors that influence the crack filling and the self-healing anticorrosion function. The established quantitative relationship shows that the filling depth of the crack in the coating is proportional to the microcapsule parameters and coating thickness, but inversely proportional to the crack width. Based on the above theoretical model, the effects of various parameters on the anticorrosion performance were experimentally studied. The actual filling of small in-situ cracks (<100 μm) generated by impact damage was semi-quantitatively characterized using scanning electron microscopy (SEM). The filling behavior is consistent with the theoretical modeling. After being healed at room temperature for 2 days upon impact damage, the formulated self-healing coatings were subjected to accelerated corrosion tests in 10 wt% sodium chloride (NaCl) solution for 2 days to observe their anticorrosion behavior. Compared to the neat epoxy coating, all the formulated self-healing epoxy coatings show evident anticorrosion function. Good self-healing anticorrosion performance was achieved by adding 10.0 wt% microcapsules with a size of 100–150 μm to the coating with a thickness of 300 μm. The results of this investigation laid a theoretical and technical foundation for the further development of both the self-healing chemistry and the self-healing anticorrosion coating.     

Self healing coatings containing dual active agent loaded urea formaldehyde (UF) microcapsules

Urea formaldehyde (UF) microcapsules loaded with linseed oil and mercaptobenzothiazole (MBT) as core materials have been synthesized by in situ emulsion polymerization. The capsules were characterized by FTIR. Surface morphology of microcapsules was analyzed using scanning electron microscope. The thermal stability of the microcapsules is in the temperature range around 600 °C as confirmed by TG analysis. The open circuit potential measurements have shown that the coatings with microcapsules maintain the potential in the noble range (≈−0.390 V vs. SCE) while the coating without microcapsules exhibit potentials in the active range. EIS studies at the artificial defect area have shown that the coating containing microcapsules is able to protect steel in neutral media since the impedance values remained at 10⁷ Ω cm² even after 15 days exposure where as the coatings without microcapsules have lost their protection ability. The self healing ability of the coating containing microcapsules was studied by SVET.     

Corrosion study of hybrid sol–gel coatings containing boehmite nanoparticles loaded with cerium nitrate corrosion inhibitor

To improve the corrosion protection of sol–gel derived hybrid silica/epoxy coatings containing boehmite nanoparticles, inorganic corrosion inhibitor was introduced into the coating via encapsulation in the nanoparticles. The morphology and chemical structure of the deposited films were studied by Scanning Electron Microscopy (SEM) and Fourier Transformed Infra-red Spectroscopy (FT-IR). The anticorrosion and self-healing properties of the coatings were evaluated by Electrochemical Impedance Spectroscopy (EIS). The high corrosion resistance performance of such coatings is due to the presence of encapsulated cerium nitrate corrosion inhibitor that can be released at the defects within the coating, hindering the corrosion reactions at defective sites.     

The study on the mechanical properties of PU/MF double shell selfhealing microcapsules

The self-healing microcapsules can be buried in the coating to improve the anticorrosive ability. In this paper,self-healing microcapsules of polyurea(PU)/melamine resin(MF) double shell were prepared by in-situ polymerization and interfacial polymerization with isocyanate as the core material. Scanning electron microscope was used to observe the microcapsule morphology. The structures of microcapsules prepared with different chain extenders were characterized by Fourier transform infrared spectroscopy. The micromanipulation system was used to loading–holding, loading–unloading and loading to rupture individual microcapsules, so as to explore the mechanical properties of microcapsules. The Young's modulus corresponding to microcapsules was calculated by mathematical model fitting. The self-healing properties of microcapsule coating were characterized by optical microscope. The experimental results showed that the microcapsule shell prepared under optimized conditions had a complete morphology and good mechanical properties. The microcapsule was in the elastic deformation stage under small deformation, and the plastic deformation stage under large deformation. The Young's modulus range of microcapsules was 9.29–14.51 MPa, and the corresponding Young's modulus could be prepared by adjusting the process. The surface crack of the coating containing microcapsule could heal itself after48 h in a humid environment.     

Antibacterial self-healing anticorrosion coatings from single capsule system

It is highly desirable to develop self-healing anticorrosion coatings with enhanced antibacterial function to prevent the scratched area to be fouled or corroded in harsh environments. Herein, we report antibacterial self-healing anticorrosion coatings via the simple incorporation of the easily synthesized single polymer microcapsule system. Well-defined polymer microcapsules containing isophorone diisocyanate (IPDI) as a healing agent and 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) as antibacterial molecules were synthesized by one-pot polymerization. The diameter and core fraction were around 30 μm and 90%, respectively. The active DCOIT content in the core material could be precisely controlled by adjusting the DCOIT/IPDI feeding ratio. The DCOIT/IPDI microcapsules-embedded protective coating exhibits an adaptive self-healing anticorrosion property, as shown by electrochemical test under the condition of the salt-water immersion. Furthermore, the self-healing coating showed efficient antibacterial function against Escherichia coli and Pseudomonas aeruginosa, which is due to the released active biocide molecules on the damaged surfaces. In contrast to other systems, this single capsule system without any catalyst is perspective for extending the service time of the antibacterial self-healing materials in harsh environment.