Crosslinked polyurethane–epoxy hybrid emulsion with core–shell structure

An epoxy resin was used to prepare crosslinked polyurethane hybrid emulsion through the blocked NCO prepolymer mixing process. Due to their hydrophobicity, the amine chain extender, blocked –NCO, and epoxy are located inside the emulsion particles. Thus, the crosslinking reaction occurs mostly in the interior of the particles. In this way, the crosslinking density of the resin is increased without the use of solidifying agents or heating during film formation, and the stability of the emulsions remains uninfluenced. The effects of the type of amine chain extender and the type, dosage, and addition mode of the epoxy resin were studied in terms of mechanical properties and swelling properties in water and toluene of the cast films. Additionally, the stability of the single-pack hybrid emulsion was studied. The results showed that the sample prepared with diethylene triamine had good stability, chemical resistance, and high mechanical strength. The modulus and water resistance of the films increased with the epoxy resin content, which could reach 20 wt%. The type of amine chain extender affected the stability of the emulsions significantly. The molar ratio of NH/NCO at 1:1 led to the best film performance. The optimal temperature of the chain-extension reaction was approximately 80°C. The hybrid emulsions could be stored for at least 6 months without apparent performance changes.