Abstract
Dual component microencapsulated hydrophobic amine and microencapsulated isocyanate were designed and fabricated for self-healing anti-corrosion coating. In this system, novel hydrophobic polyaspartic acid ester (PAE) and isophorone diisocyanate (IPDI) were microencapsulated respectively with melamine-formaldehyde (MF) as shell via in situ polymerization. To reduce the reaction activity between shell-forming MF prepolymer and PAE, another self-healing agent tung oil (TO) was dissolved in PAE and subsequently employed as core material. With field-emission scanning electron microscopy (FE-SEM) and optical microscopy (OM), the resultant microencapsulated IPDI with diameter of 2–5 μm showed a spherical shape and smooth surface. More importantly, both the morphology and microstructure of microencapsulated PAE enhanced significantly after addition of TO. Fourier transform infrared spectra (FTIR) analysis confirmed the molecular structure of chemical structure of the microcapsules. Thermal gravimetric analysis (TGA) indicated that both kinds of microcapsules exhibit excellent thermal resistance with the protection of MF shell. Furthermore, the self-healing epoxy coating system containing microencapsulated IPDI and microencapsulated PAE/TO was prepared and investigated. From the micrographs of true color confocal microscope (TCCM), the self-healing coating containing dual-component microcapsules showed excellent self-repairing performance compared to single microencapsulated IPDI system, and the optimal content of dual-component microcapsules in epoxy coating was 20 wt % approximately.
Highlights
Corrosion of metals has become a worldwide issue, which may lead to severe structure failure and dramatic economic loss [1]
After isophorone diisocyanate (IPDI) and polyaspartic acid ester (PAE)/tung oil (TO) were microencapsulated by MF shell, respectively, the dual-component microcapsules dried powder was incorporated into epoxy resin solution and the self-healing performance was further studied systematically in this work
IPDI microcapsules were synthesized via in situ polymerization in an O/W emulsion: 135 g deionized water, 15 g SMA and 20 g IPDI were mixed in a 400 mL beaker, the mixture was emulsified by a homogenizer at 8000 rpm for 10 min to obtain a stable emulsion. 30 min of vacuum degassing (0.8 MPa) was used to remove the air bubbles and dissolved gas in the emulsion
Summary
Corrosion of metals has become a worldwide issue, which may lead to severe structure failure and dramatic economic loss [1]. DCPD, poly dimethylsiloxane (PDMS), glycidylmethacrylate, epoxy, isocyanates, drying oil, and aliphatic amines and so on are selected as typical healing agents and microencapsulated [8,9] Isocyanates, such as isophorone diisocyanate(IPDI) [10,11,12], hexamethylene diisocyanate (HDI) [13,14,15], HDI trimer [16] and polyaryl polymethylene isocyanates (PAPI) [17] can react with moisture and are being used as potential healing agents to develop catalyst-free self-healing materials in moist or aqueous environments. 2,4-diisocyanate (TDI) or 4,4-diphenylmethane diisocyanate (MDI) were often inevitably employed to form the PU shell during the interfacial polymerization It appears that rapid microcracks propagation always occurred in the organic coating, while the reaction speed between isocyanate and water is usually slow especially in a low-humidity environment and low temperature [11,18]. After IPDI and PAE/TO were microencapsulated by MF shell, respectively, the dual-component microcapsules dried powder was incorporated into epoxy resin solution and the self-healing performance was further studied systematically in this work
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