Effect of polyoxyl 40 hydrogenated castor oil on pellet formation using silicon dioxide as an extrusion-spheronization aid

Abstract

Colloidal silicon dioxide (CSD) has been shown to be a potential extrusion-spheronization aid. A surfactant solution is, however, necessary to be incorporated in formulation as a binding liquid. The effects of surfactant on pellet formation have not been reported. The objectives of this study were to investigate the effect of surfactant, polyoxyl 40 hydrogenated castor oil (HCO-40), concentrations in the formulation of fumed hydrophilic silicon dioxide pellets. The formulations were composed of CSD to HCO-40 solution at a ratio of 1 to 2 by weight. Properties of materials, such as surface tension and viscosity of binding liquids, liquid uptake and binding ability of CSD as well as rheology of wet masses were characterized and information obtained was used to explain behavior of pellet formation. The results showed that rounded pellets and reproducibility of yield in target size (0.71 – 1.4 mm) were obtained from the formulation containing 2.5% w/w surfactant. The lower surfactant concentrations gave bigger pellets or agglomeration, while the higher surfactant concentrations produced rod shaped pellets. This could be explained that interaction between water-silanol groups was significant in the wet mass with the low concentrations of surfactant, evidenced by an increase in desorption temperature. At the high concentrations of surfactant, this interaction was reduced leading to more solid structure caused by interaction of silanol-silanol groups as observed in viscoelastic properties and extrusion forces. The balance between these interactions would induce an appropriate deformability of wet masses.