ISOCYANATE MICROENCAPSULATION FOR POLYURETHANE-BASED ADHESIVE APPLICATIONS
The high toxicity presented by the reactive component isocyanate (-NCO) has stimulated the creation of restrictive regulations for its use in several industries. Aiming to overcome these restrictions, the footwear industry seeks solutions to increase the bonding performance of its polyurethane-based adhesives without using isocyanate in its free form. The solution found to this problem was the microencapsulation of this component. This way, it is protected by a polymeric shell, and at the right time, it must be activated by the action of temperature and pressure, allowing the occurrence of the curing reaction, which guarantees the proper performance of the adhesive. The purpose of this work is to obtain poly(methyl methacrylate) (PMMA) microcapsules containing active -NCO groups in the core through solvent evaporation technique in oil-in-water emulsions to obtain one-component polyurethane-based adhesives for application in the footwear industry. Seeking to tailor the final properties of the microcapsules for the application in question, the influence of surfactant concentration, stirring speed, initial volume of isocyanate, initial mass of PMMA, and temperature and time in the system were studied. Depending on the combination of parameters applied, spherical shaped microcapsules were obtained, presenting core-shell morphology, with approximately 13 wt.% of active isocyanate in the core and an average diameter of 50.3 µm.