Polyurea-acrylic hybrid emulsions: Characterization and film properties

Abstract

A polyurea macromer (PUM) nanodispersion acted as a reservoir of stabilizing agent for a thermally initiated acrylic emulsion polymerization process to form binders characterized by a highly phase separated core-shell morphology. The synthesized binders (referred to as PUM-Binders) exhibited distinct dried film mechanical properties that were tied to both the state of hydration and morphology. Films from PUM-Binders exhibited higher König hardness and storage modulus when compared to films from blends of traditional acrylic latex with PUM nanodispersion at the same PUM level. König hardness and modulus increased with increasing levels of PUM for both approaches, however the closed cell foam morphology of the PUM-binder films exhibited optimal hardness and modulus retention. A separate set of PUM-Binders was prepared with varying levels of butyl acrylate (BA) and methyl methacrylate (MMA). Mechanical properties of the resulting transparent films were evaluated by dynamic mechanical analysis (DMA) and by tensile strength measurements. It was found that both tensile strength and elongation decreased with increasing BA. Increasing levels of BA were hypothesized to lead to higher degrees of phase separation between PUM and acrylic. Finally, a specific PUM/acrylic blend zone in the shell is assigned and attributed to the property differences observed.