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

Abstract

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.

Review on Adhesives and Surface Treatments for Structural Applications: Recent Developments on Sustainability and Implementation for Metal and Composite Substrates

“…PUa/PU shell MCs containing high loadings of IPDI in the core were developed to enable the production of mono-component, eco-friendly, and safer adhesive formulations for the footwear industry [ 105 ]. MCs containing not only IPDI, but also commercial isocyanate oligomeric and prepolymeric species, have been successfully developed [ 105 , 106 , 107 ] for this particular application, but also for other applications, such as self-healing in epoxy resin matrices [ 108 , 109 ].…”

Self-healing and corrosion performance of polyurethane coating containing polyurethane microcapsules

“…The collision of micro-cracks associated with the degradation and mechanical damage of the protective coating (containing micro/nano capsules) results in the release of the healing agent followed by a reaction with the passive matrix to repair the defective coating. The healing agent would react with oxygen, 8 moisture, 9 sunlight, 10 or other crosslinkers 11 to develop a new layer. Besides, using microcapsules containing suitable healing material could considerably enhance the corrosion performance of protective coatings.…”

Development of a dual capsule self‐healing silicone composite using silicone chemistry and poly(melamine‐urea‐formaldehyde) shells

“…11,12 The versatility of microencapsulation technologies offers an unlimited combination of core and shell materials for the selfhealing of surfaces. 13 Encapsulation of dicyclopentadiene, 3,14,15 epoxies, [16][17][18][19][20] polydimethylsiloxanes, [21][22][23][24] and isocyanates, 25 inside various polymeric shells such as ureaformaldehyde, 17,20,[26][27][28] melamine-formaldehyde, 10,29 melamine-urea-formaldehyde, [29][30][31] polymethylmethacrylate, [32][33][34] silica, 35 and so on, are investigated for self-healing purposes. The fabrication of microcapsules can be divided into physical or chemical methods.…”