Comparing and contrasting the properties of urethane/acrylic hybrids with those of corresponding blends of urethane dispersions and acrylic emulsions

Abstract

In this work the effect of acrylic emulsion design on polyurethane–acrylic emulsion blend properties has been examined. A series of model acrylic emulsions were prepared and blended with a commercial polyurethane dispersion (PUD). Corresponding polyurethane/acrylic hybrid (U/A) systems were prepared from the same commercial PUD. The acrylic to urethane ratio was kept at 50:50 by weight throughout. The acrylic emulsion parameters varied were: particle size, composition (acid monomer level), T g and molecular weight. Modulated DSC was used to qualitatively determine the amount of polyurethane and acrylic polymer in the interphase of the blends and hybrids. Results show that there is approximately 5–20% by weight of each of the acrylic and polyurethane in the interphase in the blends. While in the U/A hybrids there is approximately 20–30% polyurethane and 35–50% of acrylic in the interphase. The mechanical properties of the dry films were measured by tensile testing. The hybrids were found to compare favorably with, and in some areas exceed, the PUD alone in tensile performance. In contrast the performance of all of the blend systems fell short of the PUD and of the corresponding hybrids. Within the set of blends the best tensile results were achieved using the low T g, high molecular weight acrylic emulsions. There were no clear trends with changes in acrylic emulsion particle size or acid content. The difference in performance between blends and hybrids is attributed to the increased phase mixing and the improved dispersion of phase domains in the hybrids.