Tailoring rheological properties of uncrosslinked water-borne pressure-sensitive adhesives by means of polymer maximum volume fraction

Abstract Pressure-sensitive adhesives (PSAs) based on butyl acrylate (BA), 2-ethylhexyl acrylate (2-EHA), methyl methacrylate (MMA), vinyl acetate (VAc), and acrylic acid (AA) were prepared via semicontinuous emulsion polymerization, the obtained latexes having nanometer particles, narrow monomodal particle size distribution, and concentrations close to maximum packing fraction. The rheological behavior of liquid adhesives was described using the generalized Maxwell model and the observed differences are a consequence of different particle surface polarity. As the copolymers polarity increases by incorporation of VAc, the amount of surfactant deposited onto the particles decreases, which leads to lower viscosities and higher values for critical volume fraction of polymer. The viscoelastic properties of solid adhesives were investigated by Dynamic Mechanical Analysis. Copolymers of MMA have higher glass transition temperatures than what would be expected theoretically, indicating a higher cohesive strength for these copolymers. Moreover, MMA copolymers have lower molecular masses between entanglements than those containing VAc. All these viscoelastic characteristics are in very good agreement with the adhesive performance characteristics observed.