Texicryl Alkali Swellable Emulsions (ASEs)
Texicryl alkali swellable emulsions (ASEs) are dispersions of acid-functional acrylic polymers in water. These emulsions are supplied at low pH, meaning that acid groups on the polymer chains must be neutralized to allow the polymer to swell and thicken.
Under acidic conditions, the polymer exhibits a tight, coil-like structure. Adding alkali to the system increases pH, which causes the acid functional groups on the thickener to start dissociating. As it begins to uncoil, the thickener becomes more water-soluble.
Further increases in pH cause the polymer to adopt a more open long-chain structure, causing thickener molecules to become entangled. This process increases viscosity (pictured schematically below).
Image Credit: Scott Bader Company Ltd.
Formulation Guidelines for Texicryl ASEs
Thickeners are typically supplied at 30% solids and low viscosity. They are suitable for straightforward mixing into aqueous-based systems, and it is often possible to add thickeners directly to the desired system, adjusting pH where necessary.
The thickened formulation’s final pH should typically be between 8.0 and 9.5 to ensure an ideal thickening efficiency and a reliably stable viscosity. Care should be taken to avoid loss of the alkali and lowering of the pH when a volatile alkali such as ammonia is used because this can reduce viscosity.
Sometimes, diluting the thickener (up to 2:1 with water) may be necessary. This should be done before addition to latex systems to avoid any instability or localized thickening.
It is also possible to prepare a pre-gel in cases where there is a risk of localized gelation and instability. This approach should involve implementing at least two parts water to one part thickener to obtain a handleable gel, followed by neutralization. Extra care should be taken to avoid air entrainment.
Texicryl Hydrophobically-Modified Alkali Swellable Emulsions
Texicryl hydrophobically-modified alkali swellable emulsions (HASE) are water dispersions of acid-functional acrylic polymers. Much like conventional ASE types, these emulsions are supplied at low pH, and there is a need to neutralize acid groups on the polymer chains to allow the polymer to solubilize.
In addition to the acid groups, HASE systems also feature long-chain hydrophobes attached to the polymer backbone.
When used in a formulated system, these hydrophobic groups can associate with one another to form micelles analogous to surfactants and other hydrophobic ingredients. Due to this particular behavior, HASE thickeners are called ‘associative thickeners’.
The multiple associations between the HASE thickener and various formulation ingredients notably impact a given system's rheological properties. For example, HASE thickeners typically achieve a more Newtonian rheology than standard ASE thickeners.
HASE thickeners can also be designed to provide formulated system rheologies that range from pseudoplastic to relatively Newtonian, depending on the polymer design and the nature of the hydrophobe.
Rheology and Efficiency
The graph here indicates the relative rheological behavior of Scott Bader’s range of Texicryl thickeners in a basic paint formulation.
Texicryl 13-313 is a very efficient thickener featuring a high, low-shear viscosity and exceptional pigment suspension characteristics. It is relatively strongly shear-thinning, but it does exhibit somewhat different flow characteristics versus a standard ASE thickener.
In contrast, Texicryl 13-317 exhibits far less shear thinning behavior and a more Newtonian character, resulting in higher viscosities in the mid-and high-shear rate ranges. This thickener also boasts improved flow, enhanced leveling, optimal brush drag, and robust film build.
Image Credit: Scott Bader Company Ltd.
Thickening Mechanism of HASE Thickeners
The diagrams below highlight the appearance of HASE thickeners in water and a system containing latex particles.
Image Credit: Scott Bader Company Ltd.
Acknowledgments
Produced from materials originally authored by Scott Bader Company.
This information has been sourced, reviewed and adapted from materials provided by Scott Bader Company Ltd.
For more information on this source, please visit Scott Bader Company Ltd.