Thickening Effect of Commercial Associative Thickeners on the Latices of Copolymers of Acrylic Monomers Carrying Hydrophilic Reactive Groups

Abstract

Investigation of flow properties of butyl acrylate/styrene/2‐hydroxyethyl methacrylate/acrylic acid latices thickened by commercial associative thickeners based on hydrophobic ethoxylated urethane (HEUR) or hydrophobically modified alkali‐soluble emulsions (HASE) showed that the apparent viscosity, at a constant medium shear rate, increased with the increasing content of 2‐hydroxyethyl methacrylate (HEMA). In contrast, the relative change in latex viscosity after the thickener addition (thickening efficiency), expressed as the ratio of viscosities of the thickened and untreated latices, decreased. This indicates that the increase in viscosity of the thickened latex with a higher HEMA content is caused by the increasing viscosity of the untreated latices due to rising hydrodynamic volume of alkalinized latex particles and not by higher particle bridging with the thickener macromolecules. The HEMA monomer clearly increases hydrophilicity of the particle surface which reduces adsorption of hydrophobic ends of the thickener on latex particles and the thickening efficiency decreases.

Keywords:

• Latices of acrylic copolymers containing 2‐hydroxyethyl methacrylate groups
• Associative thickeners
• Thickening efficiency

Acknowledgment

The Grant Agency of the Czech Republic is gratefully acknowledged for supporting this work by grant No. 104/99/0560. The work was also funded by the Ministry of Education of the Czech Republic in frames of Project MSM 2531 00001.