Hybrid shell microcapsules containing isophorone diisocyanate with high thermal and chemical stability for autonomous self-healing of epoxy coatings

Silica-polyurea/polyuretane hybrid shell microcapsules (MCs) loaded with isophorone diisocyanate (IPDI) with long shelf-life and high thermal and chemical stability are prepared via emulsification followed by interfacial polymerization at the surface of oil droplets of the oil-in-water emulsion. The resultant MCs are aimed at self-healing performance in epoxy coatings. A commercially available, highly reactive polyisocyanate named tris(p-isocyanatophenyl) thiophosphate is successfully employed as shell forming agent, while triethoxyoctylsilane and hexadecyltrimethoxysilane (HDMS) are tested as “latent” active hydrogen sources. The resulting MCs display core–shell morphology, spherical shape with diameter of 5–20 μm, shell thickness ca. 1–2 μm, and an IPDI core fraction of 69 and 65 wt %, when HDMS and triethoxyoctylsilane are employed, respectively. MCs exhibit an increased thermal stability, comparing with pure IPDI, which makes them robust enough to resist the thermal cycles involved in the coating's preparation. Stability of MCs inside specific solvents and chemicals, their chemical composition and shelf-life as well as effect of MCs on the epoxy curing are evaluated by Fourier transformed infrared spectroscopy. MCs, remarkably, show excellent environment stability and a long shelf-life of more than 3.5 months. Their addition to an epoxy formulation is found to heal damaged zones in the epoxy coating, as shown by scanning electron microscopy and electrochemical impedance spectroscopy. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48751.     

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.     

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.     

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.     

基于六官能度异氰酸酯用于自修复防腐涂料的微胶囊的制备与表征

微胶囊自修复技术是将自修复微胶囊埋植于基体,在破坏后实现自我修复。IPDI作为低官能度异氰酸酯在湿气中固化修复能力有限,本文设计基于六官能度异氰酸酯DiPE-IPDI/DiPE-TDI合成用于自修复防腐涂料的新型微胶囊,着重对六官能度异氰酸酯DiPE-IPDI合成过程中溶剂、温度进行反应条件优化,通过傅里叶红外光谱、核磁等对产物结构进行表征。同时对微胶囊制备过程中粒径结构进行可控组装, 通过TGA/DSC表征该自修复微胶囊热力学性能。制备负载微胶囊的自修复环氧树脂基防腐涂料,盐雾试验结果显示其具有优异的自修复性能。     

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.     

Fabrication of Core–Shell Novel Polyurea Microcapsules Using Isophorone Diisocyanate (IPDI) Trimer for Release System

Isophorone diisocyanate (IPDI) trimer based novel polyurea core shell structures were developed by interfacial polymerization. Different operating conditions have been used to fabricate shell to encapsulate core. Characterizations of prepared microcapsules were done by Fourier transform infrared spectroscopy, thermogravimetric analysis, and particle size analyzer. The surface morphology of microcapsules was examined by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The release rate of core from microcapsules was estimated by UV and gas chromatography. The results revealed that tailor made release can be adjusted by varying operational protocol for shell and fabricated shell can be extended to other applications such as self-healing coatings and drug delivery.     

Optimization of microencapsulation of polyaspartic acid ester into UV curable epoxy-acrylate resin using Taguchi method of experimental design

Due to fast reaction with isocyanates, polyaspartic acid esters (PAAE) can be used for the development of microcapsules for self-healing coatings. Microcapsules with encapsulated PAAE into shell formed by UV-cured commercial epoxy-acrylate resin were produced through oil-in-water emulsion polymerization triggered by UV light. The obtained microcapsules were characterized by FTIR, TGA, optical microscopy, and SEM. Various encapsulation parameters, including core to shell ratio, agitation speed, emulsifier type and concentration, solvent type and its concentration in the oil phase, have been selected at four different levels. Microencapsulation was optimized using Taguchi L16 parameter design approach for determination of desired outcome as larger is better (maximal core content) and nominal is better (microcapsule diameter of 50 μm). It was determined that conditions to prepare microcapsules with the highest core content and the microcapsule size close to 50 μm are rather similar requiring core-to-shell ratio at about 4:1, low agitation speed of 500–1000 rpm, and the use of two polymeric emulsifiers poly(vinyl alcohol) and Gum Arabic at concentration of about 2%. Primary benefits of UV-induced shell formation during microencapsulation of active compounds are remarkably shorter time of the process and possibilities to reach high core content and prepare microcapsules of desirable size.     

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。     

Facile and efficient isocyanate microencapsulation via SDBS/PVP synergetic emulsion

A binary emulsion system via combination of sodium dodecylbenzenesulfonate (SDBS) and polyvinyl pyrrolidone (PVP) was employed to prepare microcapsules containing isophorone diisocyanate. The effect of different concentrations of SDBS and PVP on the size and distribution of capsules was investigated. The results showed that uniform and size-controllable capsules were synthesized by synergistic function of SDBS and PVP. Characteristics of capsule were studied by optical microscopy, Fourier transform infrared spectrometry, scanning electron microscopy, thermal gravimetric analysis, and ¹H NMR. The results revealed that the core content and yield of the spherical capsules were approximately 65.7 and 79 wt %, respectively, at the capsule diameter of ~115 μm. The residue core content of microcapsules was approximately 44.7 wt % after immersion in water for 10 days. And its self-healing epoxy coatings showed excellent corrosion resistance performance after accelerated corrosion tests. These results exhibited the feasibility and great application prospect of the multiemulsifiers system in the microcapsule synthesis process. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48045.     

醇酸树脂微胶囊的制备及环氧涂层自修复性能

采用三聚氰胺-脲醛树脂（MUF）为壁材、合成的花椒籽油醇酸树脂为芯材，原位聚合法制备自修复微胶囊，探讨了微胶囊的制备工艺。并采用扫描电子显微镜（SEM）、红外光谱仪（FTIR）、热重分析仪（TGA）和粒径分析仪对微胶囊的表面形貌、化学结构、热稳定性及其粒径分布进行了测试表征。将醇酸树脂微胶囊分散到环氧基体中，研究了环氧涂层的力学性能和自修复性能。实验结果表明，当乳化剂浓度为2.0g/L、芯壁比为2∶1、终点pH为3.5时，微胶囊呈球形结构，无明显的缺陷和损伤，平均粒径为97.44μm，热稳定性良好。当添加质量分数5%的微胶囊时，与未添加微胶囊的自修复涂层相比，其弯曲强度、拉伸强度、黏结强度及其冲击强度分别提高了50.4%、50.0%、40.0%及25.2%，且涂层的自修复性能良好。     

Preparation and characterization of microencapsulated polythiol

Microcapsules containing curing agent for epoxy were successfully prepared by in situ polymerization with poly(melamine–formaldehyde) (PMF) as the shell material and high-activity polythiol (pentaerythritol tetrakis (3-mercaptopropionate), PETMP) as the core substance. Having been encapsulated, the core material PETMP had the same activity as its raw version. The synthesis approach was so improved that the consumption of polythiol was reduced to a low level. By carefully analyzing the influencing factors including catalyst concentration, reaction time, reaction temperature, feeding weight ratio of core/shell monomers, dispersion rate and emulsifier content, the optimum synthetic conditions were found out. The results indicated that not only core content and size of the microcapsules but also thickness and strength of the shell wall can be readily adjusted by the proposed technical route. The relatively thin shell wall (0.2 μm) assured sufficient core content even if the microcapsules were very small (1–10 μm). The polythiol-loaded microcapsules proved to be qualified for acting as the mate of epoxy in making two-part microencapsulated healing agent of self-healing composites.     

Application of EIS and EN techniques to investigate the self-healing ability of coatings based on microcapsules filled with linseed oil and CeO2 nanoparticles

Microcapsules with urea–formaldehyde as the shell and linseed oil as the healing agent were synthesized by a previously reported procedure. Two kinds of synthesized microcapsules, without and with CeO₂ nanoparticles, were separately added to the epoxy resin coatings. The epoxy coatings containing microcapsules were applied on carbon steel, and their self-healing effect was investigated in 0.5 M HCl solution. The amount of the released healing agent that filled up the scratch was estimated by scratch filling efficiency (SFE). The SFE values are only the theoretical estimates of the self-healing performance. The scratch sealing efficiency (SSE), which is a measure of corrosion protection performance of the damaged coating, can be measured by electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) techniques. For sake of an optimum self-healing system, two series of coatings, with and without nanoparticles, were prepared by using different microcapsule concentrations: 5, 10, 15 and 20 wt%. For comparison, a coating without microcapsules was also prepared. The coated samples with 5% microcapsule concentration, due to the low amount of released linseed oil, could not properly repair the artificial scratch. In contrast, when the microcapsule concentration was equal to or higher than 10% the volume of the released linseed oil was enough to seal the scratch. However, the coating sample containing 15% nanoparticle-loaded microcapsules was the optimum self-healing coating because it showed comparable SSE values to those of samples containing 20% microcapsule concentration in spite of its lower microcapsule concentration. The EN method was employed as a complementary quantitative technique to study the self-healing behavior of coatings. The calculation of the amount of noise charges using the standard deviation of partial signal (SDPS) plots arising from wavelet analysis made it possible to obtain the SSE values of the coatings. The good agreement between EIS and EN results indicates that the EN technique, as well as the EIS method, can be used successfully for the self-healing evaluation.     

Preparation and properties of bisphenol A epoxy resin microcapsules coated with melamine–formaldehyde resin

Microcapsules containing epoxy resins have potential applications, such as in adhesive, electronic packaging, and self-healing polymeric composites. A series of microcapsules were prepared by in situ polymerization with poly(melamine–formaldehyde) as the shell materials and a mixture of diglycidyl ether of bisphenol A and epoxy diluent as the core substances. Morphology, chemical structure, mean particle size, and thermal properties of the microcapsules were studied by means of optical microscope, Fourier transform infrared spectroscopy, laser particle size analyzer, and microcomputer differential thermal balance, respectively. Effects of kind of epoxy diluent, surfactant type, emulsifier concentration, and emulsifying rate on the physical properties of microcapsules were investigated. Results indicate that the formation of microcapsules is affected by the epoxy diluent type and surfactant type. The highest core content of the resultant microcapsules is about 88 wt% and average diameters of the capsules range from 67 to 201 μm, which can be adjusted by changing the emulsifier concentration and emulsifying rate. Thermo gravimetric analysis indicated that the prepared microcapsules experienced excellent stability up to 235 °C.     

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.     

异氰酸酯胶囊型自修复高分子材料研究进展

回顾了微胶囊型自修复高分子材料中双环戊二烯-Grubbs催化剂、聚二甲基硅氧烷-锡(铂)催化剂、环氧树脂-固化剂和异氰酸酯等自修复体系的研究现状,重点介绍了异氰酸酯胶囊型自修复材料的修复机理和研究新进展。异氰酸酯胶囊型自修复是通过异氰酸酯修复剂(主要是异佛尔酮二异氰酸酯、六亚甲基二异氰酸酯及其三聚体等)潮固化来实现,并简要探讨了影响微胶囊自修复高分子材料自修复效果的主要因素(微胶囊的芯材、力学性能以及微胶囊与基材的相容性)。最后指出了微胶囊型自修复高分子材料今后的研究方向(建立自修复过程的模型,将微胶囊应用到存在一些如晶界、气孔等微结构的材料中)及其应用前景(提高航空航天和民用高铁等高速高风险项目的可靠性,开发自修复涂料、胶黏剂等)。     

Hybrid organosiloxane coatings containing epoxide precursors for protecting mild steel against corrosion in a saline medium

Hybrid organic–inorganic materials made from sol–gel precursors can be used as anticorrosion barriers on metal substrates. The modification of epoxy resins with silicones is an interesting approach toward the synthesis of hybrid materials that combine the advantages offered by epoxy resins with those of silicones. In this study, novel hybrid epoxy‐silicon materials were synthesized using sol–gel chemistry and subsequently functionalized with 4,4′‐methylenebis(phenyl isocyanate), incorporating urethane functionality into the final polymer. The study screened five different epoxide precursors for use in the synthesis of the new hybrid materials and optimizing their anticorrosion properties. Spectral characterization confirms the proposed chemical structures of the newly synthesized polymers. The newly developed polymers were painted on mild steel panels, thermally cured, and their thermal, surface morphological, adhesion, and anticorrosion properties were fully characterized. The new coatings were found to have excellent thermal stability and adherence properties to steel surface. The results of corrosion testing on coated steel panels following long‐term immersion in a 3.5 wt % aqueous NaCl medium revealed that the polymer prepared using the epoxide precursor bisphenol A diglycidyl ether provided the best anticorrosion protection property among the synthesized polymers. This could be attributed to the excellent integrity and crosslink density properties in addition to the lack of microdefects in the surface of this coated sample as confirmed by scanning electron microscopy analyses. The newly prepared hybrid coatings reported in this study are very promising as an alternative to toxic chromate‐based coatings. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43947.     

Designing of polyamidoamine-based polyurea microcapsules containing tung oil for anticorrosive coating applications

A novel method for the fabrication of robust polyurea microcapsules containing tung oil as a core material was developed for self-healing anticorrosive coating application. Well-distinct microcapsules with polyurea as a shell were prepared by reacting hexamethylene diisocyanate trimer with 0.0 G polyamidoamine (PAMAM) via interfacial polymerization technique. Fourier transform infrared spectroscopic analysis was performed to elucidate the chemical structure of microcapsules as well as to confirm successful encapsulation of core by the polyurea shell. Surface morphology, particle size, distribution of particle size, thermal, and mechanical properties of the prepared PAMAM-based polyurea microcapsules were compared with microcapsules that were prepared using diethylenetriamine (DETA) and triethylenetetramine (TETA). The prepared microcapsules were embedded with acrylic polyol-based polyurethane (PU) coatings to ensure anticorrosive performance. The immersion study of self-healing PU coatings loaded with 5% PAMAM-based polyurea microcapsules possesses satisfactory anticorrosive property under an accelerated corrosion process in 5% NaCl salt solution.     

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.     

硅烷改性环氧树脂自修复微胶囊的制备及应用

采用硅烷偶联剂γ-（2,3-环氧丙氧基）丙基三甲氧基硅烷（KH-560）对环氧树脂E-51进行改性,并以此为芯材,三聚氰胺-脲醛树脂（MUF）为壁材,原位聚合法合成微胶囊,探讨了微胶囊制备工艺,并用光学显微镜（OM）、扫描电子显微镜（SEM）、红外光谱仪（FTIR）、热重分析仪（TGA）等对其表面形貌、化学结构及热性能等进行了表征和测试;之后将改性后的微胶囊应用到自修复环氧树脂涂层中,考察了自修复涂层的力学性能和电化学性能。结果表明,当芯壁比为1.5：1、乳化剂质量分数为1.4%时,微胶囊为规则球形,表面粗糙、致密,大小均匀,平均粒径约为100μm,具有良好的热稳定性。当涂层中改性微胶囊质量分数为3%时,涂层的拉伸强度、弯曲强度、黏结强度及冲击强度均较高,且其较未改性微胶囊自修复涂层分别提高了14.9%、14.3%、16.0%和9.6%;与未改性微胶囊自修复涂层相比,改性微胶囊自修复涂层的电化学性能增强,且电化学阻抗值显著提高。