Hydrogenated castor oil is a good organic thixotrope or rheological additive (RA) because excellent performance can be obtained from this wax, provided that the additive is dispersed and activated in a specific manner. The rheological additive provides anti-settling effects, and controls flow and levelling, as well as the degree of sagging in coatings. The glyceride moiety in castor wax can be replaced by amine functional materials to yield wax-like amides of 12-hydroxy stearic acid. These amides are also quite effective as rheological control agents, and they complement hydrogenated castor oil to yield an effective castor wax portfolio of materials for the paint formulator to choose from. The castor-derived 12-hydroxystearic acid moiety is an effective rheological component because it can self-assemble into spatially preferred structures, some of which extend throughout the formulation and effectively trap solvent and/or resin, and thereby control the material flow. An example of such a network is shown in Figure 1.
Finely milled powders of castor wax must be subjected to solvent wetting, de-agglomeration and high-shear dispersion forces at specific temperatures to unlock rheological benefits. Castor wax-based rheological additives have specific processing temperature requirements that are related to the solvency that are present in a paint system. Therefore, the most appropriate choice of castor-based rheological additives for any given system depends on solvent type(s), processing temperature control and the manufacturing equipment. An optimal combination of these parameters allows for the most effective level of colloidal dispersion and yields a rheologically active network. With proper use, a castor-derived rheological additive provides outstanding efficiency for thixotropic (shear thinning) viscosity build, sag control and pigment suspension.