Understanding the activation of low– to medium–polarity bentonite as a rheological modifier in organic coatings

Rheological modifiers are essential for controlling the flow behavior of paint and adjusting characteristics like leveling, sagging, settling, and thixotropy. Bentonites, natural phyllosilicate clays, require an activation process to function as rheological modifiers to improve the sag resistance of paint. This study aims to understand the role of bentonite as a rheological agent in organic coatings, evaluate the factors influencing its activation mechanism, and propose a method that maximizes its benefits. It was found that an optimum type and amount of polar solvent are crucial for the best activation. Solvents like methanol and ethanol, which are highly polar, small in molecular size, and capable of forming hydrogen bonds, are the most effective. However, these solvents play a minimal role in the intercalation and exfoliation of bentonite layers during production. Instead, they increase viscosity by forming intermolecular bonds between platelets. It was observed that ultrasonic processors and inline dispersers are more effective tools for activation, as they provide higher shear rates and can increase the temperature, facilitating the mobility of platelets and polar activators to form bonds. With the optimal activation procedure, the sag resistance film thickness was increased from 138 to 250 µm using the same amount of bentonite.