The structure and properties of core-shell type acrylic-polyurethane hybrid aqueous emulsions

Abstract

Three types of core-shell type acrylic-polyurethane hybrid aqueous emulsions were prepared by soapfree emulsion polymerization techniques. The formation of core-shell morphology was clearly observed by transmission electron microscopy in the case of A/U-type emulsions whose core and shell regions are occupied by acrylic polymer and polyurethane, respectively. The size and the distribution of emulsion particles are found to vary drastically depending on the chemical composition of core and shell parts and core-shell ratio. The surface properties of the dried clear films formed from A/U-type hybrid emulsions were studied by FT-IR, ESCA and contact angle measurements. The results of these three methods support the idea that the surface layer of dried clear films is rich in polyurethane component. A/U-type emulsion and A/U-A-type emulsions whose shell part is formed by polyurethane-acrylic graft copolymer showed similarly excellent adhesion properties onto various plastic films for food packaging uses. Functional groups which are expected to react with each other after the evaporation of water are introduced into core and shell regions (in the case of U/A-type emulsions) or core region and aqueous phase (in the case of A/U-g-A-emulsion). The effect of the crosslinking reaction between and within particles was observed by thermomechanical analysis. The reaction of these functional groups was studied by FT-IR measurements using a water-soluble model polymer containing ketone groups and a low molecular crosslinking agent containing hydrazide groups. In the course of the dry film formation from aqueous emulsions, the formation of imino bonds between ketone groups and hydrazide groups was observed.