Rheology Modifiers in Paint and Coating Applications

Rheological modifiers are sometimes referred to as thickeners or viscosity regulators, but they do much more than simply thickening or adjusting the consistency of a formulation. They impart low viscosity or thixotropic properties to wet paint through shear force. For this reason, rheological modifiers can prevent settling during transport and storage, but may allow the product to sag or flow during application.

Rheological Modifiers Are Divided into Two Categories;

• Inorganic Modifiers; - Clay, - Fumed Silica, - Specialty Clay. • Organic Modifiers; - Cellulosic, - Synthetic. * Associative type. * Non-associative type. * Other solvent-based. Inorganic Rheology Modifiers The most commonly used modified and unmodified inorganic types of rheology modifiers are attapulgite clays, bentonite clays, organoclays, and processed and unprocessed synthetic silicas. When most inorganic thickeners and rheological modifiers are homogeneously dispersed in a coating, they typically function as suspending or gelling agents, and some can present secondary functional use as extenders for pigments. Inorganic rheology modifiers tend to have high efficiency values and thixotropes are characterized as follows: the viscosity of the formulation generally begins to decrease over time and gelling is observed. When the usage amount is adjusted by % dosing with the mineral type of rheological additives added and mixed into the formulation, problems from the medium will be resolved. For this reason, using this type of thickener would be beneficial.

Organic Rheology Modifiers

Organic rheology modifiers are more diverse than inorganic ones. They consist of products based on natural raw materials. Materials such as cellulose and xanthan and products based on them are synthetic chemicals such as polyacrylates or polyurethanes. Synthetic products are divided into two categories: associative products and non-associative products. Associative-type rheology modifiers (Associative Type): these thicken through non-specific interactions of hydrophobic groups. The end groups of a thickener molecule form a structure called a "physical network" with both themselves and coating components. Unlike non-associative types, associative thickeners interact with polymer dispersions used as binders. The hydrophobic terminal and side groups of these thickeners combine to form networks that serve to increase viscosity. Non-associative-type rheology modifiers (Non-associative type): these operate through high molecular weight entanglements with high solubility. The effectiveness of polymer chains ("hydrodynamic thickening") in a non-associative thickener is essentially controlled molecularly. Formulations thickened non-associatively by polymer weight have pseudoplastic rheology with high elastic properties. This provides good stabilization against settling and low sag. Even for high-build coatings. Non-associatively thickened systems generally exhibit limited fluidity. High molecular weight polymers can sometimes lead to compatibility issues such as flocculation.

Rheological Modifiers for Water-Based and Solvent-Based Systems

[caption id="attachment_132702" align="aligncenter"] * Advantages and limitations of polyurethane/polyether and acrylic rheological modifiers[/caption]  

References 1. Solvent Based Systems – Guihuachem 2. 23.pdf (teb.org.tr) 3. Basf Solvent-based-systems rheology

 

Cihat Günay Business Development Manager Günkem