The role played by different active hydrogen sources in the microencapsulation of a commercial oligomeric diisocyanate

The present paper regards the development of polyurea/polyurethane (PUa/PU) and PUa/PU-silica hybrid shell microcapsules (MCs), loaded with Ongronat (R) 2500, a commercial type of oligomeric methylene diphenyl diisocyanate with increased functionality, as core material. Ongronat (R) 2500 has a wide range of applications either for the production of rigid polyurethane foams and as cross-linking or self-healing agent. The MCs were achieved by a facile, one-pot process, consisting of an oil-in-water microemulsion system combined with interfacial polymerization processing, employing a higher reactivity isocyanate, toluene diisocyanate, to competitively contribute to the shell formation. Ethylenediamine, polyethylenimine (PEI), triethoxy(octyl)silane (n-OTES) and 3-(2-aminoethylamino) propyltrimethoxysilane (aminosilane) were tested as active, or latent active hydrogen (H) sources, and their effect on the MCs morphology, encapsulation yield, shelf life, shell's chemical structure and thermal stability was assessed. The MCs are aimed at the development of a new generation of adhesive formulations, which are mono-component, self-reactive, eco-friendly and with low health hazards, for industries such as the footwear, construction, aerospace and automotive. MCs' characterization was performed using Fourier transformed infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. It was possible to obtain MCs with a high loading of Ongronat (R) 2500, exhibiting a core-shell morphology, an increased shell resistance to temperature and improved shelf life. The combination of PEI and n-OTES led to the best compromise between encapsulation yield and shelf life. Finally, a confinement effect of the encapsulated macromolecules is herein shown for the first time, by the drastic narrowing of the NCO peak at the FTIR spectrum of the MCs.