Acrylic acid level and adhesive performance and peel master-curves of acrylic pressure-sensitive adhesives

Three series of pressure-sensitive adhesives were prepared with constant glass-transition temperature, using emulsion polymerization. The monomers chosen were butyl acrylate, 2-ethylhexyl acrylate (EHA), methyl methacrylate (MMA), and acrylic acid (AA). Within each polymer series, the proportion of AA monomer was held constant for each polymer preparation but acrylic ester monomer levels were varied. Adhesion performance was assessed by measurement of loop tack, static shear resistance, and through the construction of peel master-curves. Peel master-curves were generated through peel tests conducted over a range of temperatures and peel rates and through application of the time-temperature superposition principle. Bulk effects dominated by polymer zero shear viscosity change as AA and EHA levels were varied were attributed to the observed effect on static shear resistance and the horizontal displacements of peel master-curves. Static shear resistance was found to strongly correlate with log(a(C)), a parameter introduced to horizontally shift peel master-curves to form a superposed, "super master-curve". An interfacial interaction was proposed to account for deviations observed when loop tack was correlated with log(a(C)). Surface rearrangements via hydrogen bonding with the test substrate were suggested as responsible for the interfacial interaction.