Hydrogenated Castor Oil Thixotrope (HCO)

Hydrogenated Castor Oil (HCO) is a natural-origin thixotropic and anti-settling additive derived by full catalytic hydrogenation of castor oil. The hydrogenation converts the unsaturated ricinoleic acid triglyceride of castor oil into a fully saturated, waxy solid (principally 12-hydroxystearic acid triglyceride) that is insoluble in most resin systems at room temperature. This insolubility is the key to HCO's function: when dispersed into hot resin (above HCO melting point, ~85°C) and allowed to cool, HCO forms a fine crystalline network that builds thixotropic structure and prevents settling of fillers and pigments.

HCO is widely used as an economical, natural-origin thixotrope in unsaturated polyester resins, alkyd resins, and paint systems. It provides good anti-sag performance in polyester putties, body fillers, and construction repair compounds where the slightly yellow-off-white color of HCO is not a concern. The thixotropic network is formed by hydrogen bonding between hydroxyl groups on the 12-hydroxystearic acid chains, creating a fibrous crystal network.

HCO is supplied as a fine white to off-white powder or flake. Unlike UMAP thixotropes which require high-shear dispersion in the cold resin, HCO must be incorporated into the resin while hot (90–120°C) to dissolve, and the thixotropic structure develops on cooling. This hot-melt incorporation requirement limits its use in systems that cannot be heated. In auto body filler (polyester putty) applications, HCO at 1–3% provides adequate anti-sag and paste consistency for the low-cost market segment.