Alkali Swellable Thickeners

Carboxyl-containing copolymers that are prepared by the polymerization of ethylenically unsaturated monomers that swell and thicken above a pH of 7 are known as alkali-swellable thickeners, or ASTs.

ASTs are classified as either non-associative or associative, depending on the way they thicken.

Alkali-swellable emulsions (ASE) are non-associative thickeners while hydrophobically modified alkali-swellable thickeners (HASE) are associative thickeners.

Both ASE and HASE are coiled polymers that expand to form a network of tangled chains that untangle upon the application of shear. As they extend, their reactivity with other ingredients increases, and hydrodynamic volume in water increases to cause thickening.

ASE and HASE differ in the way they cause thickening. ASE polymers thicken the aqueous phase of a coating or ink through hydrodynamic volume change and by molecular chain entanglement. HASE polymers thicken when their hydrophobic groups interact with each other and with other hydrophobic components present in the coating or ink.

The number of hydrophobic groups and acid functional groups in HASE polymers can be altered to increase their thickening efficiency and water retention properties.

Because associative bonds formed are relatively weak, HASE polymers flow readily upon application of low shear. While HASE polymers provide high viscosity at low shear, they quickly thin to provide low viscosity at high shear. The general molecular structures of an ASE and HASE polymer are shown below.

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ASE Polymer

HASE Polymer