Efficient encapsulation of isocyanates in PCL/PLA biodegradable microcapsules for adhesives

Abstract Microencapsulation of isocyanates eliminates the risks associated with their direct handling, protects the isocyanate species from air moisture, and increases the storage life. In light of this, we present a straightforward and efficient process to encapsulate isophorone diisocyanate (IPDI) using biodegradable polymers by an emulsion system combined with the solvent evaporation method. We produced spherical, disaggregated, and core–shell microcapsules (MCs) using poly(ε-caprolactone) (PCL), polylactic acid (PLA), or PCL/PLA blends as shell materials. As far as we know, it is the first time that isocyanate species are encapsulated by PLA or PCL/PLA blends. Our process leads to a production yield of 70–74% and an encapsulated isocyanate content up to 73 wt% of the MCs. All MCs showed very good isocyanate protection, especially when stored in low-moist environments. Their use as cross-linking agents for harmless, eco-innovative, and high-performance adhesive formulations for footwear was tested, for the first time, according to the specifications of industry standards. The peel tests of the adhesive’s joints revealed peeling strength values between 3.45 and 6.09 N/mm which is higher than the minimum required. The creep tests demonstrated that the use of MCs with encapsulated IPDI improves the heat resistance of the adhesive joints. Therefore, the MCs revealed an effective isocyanate release and very capable adhesive joints with no negative effects from the polymeric shell, validating the employment of these cross-linking agents in the footwear industry. Although PCL MCs were the ones with the highest IPDI content, the best adhesive formulations were produced with MCs with a high amount of PLA, due to their smaller size, good dispersibility and better distribution at the substrate. Graphical abstract